ci: bump actions/checkout v4->v7 in identity-guard (dependabot)

The scsi::windows::list_drives fix (build under default-features=false,
features=["scsi"]) ships in 1.7.0; add it to the changelog's Fixed list.

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: MattJackson

.github/workflows/ci.yml

@@ -11,7 +11,53 @@ on:
   pull_request:
 
 jobs:
+  # ── Single source of truth for the MSRV ─────────────────────────────────────
+  #
+  # `rust-version` in Cargo.toml is the ONE place the MSRV is declared. This job
+  # reads it; every job that must build/test AT the MSRV consumes
+  # `needs.resolve-msrv.outputs.v` instead of a hardcoded pin, so the floor
+  # cannot drift out of sync across workflow files. The `test` job building
+  # green at this value IS the verification that the declared MSRV is real.
+  # clippy and the `consumers` job deliberately do NOT use it — they run on
+  # `stable` (lint debt is caught against current Rust; dependents float highest).
+  resolve-msrv:
+    runs-on: ubuntu-latest
+    outputs:
+      v: ${{ steps.msrv.outputs.v }}
+    steps:
+      - uses: actions/checkout@v7
+      - id: msrv
+        shell: bash
+        run: echo "v=$(grep -m1 '^rust-version' Cargo.toml | sed -E 's/.*\"([^\"]+)\".*/\1/')" >> "$GITHUB_OUTPUT"
+
+  # CI owns the changelog: main may never carry a released version without a
+  # CHANGELOG.md entry for it. The release orchestrator dates an existing
+  # `## [X.Y.Z]` heading — it does NOT invent one — so a version bump that
+  # forgot its changelog entry must fail here rather than ship a blank release.
+  # Hard-fails on main (and PRs targeting main); warns elsewhere so an
+  # in-progress dev/qa branch whose entry isn't written yet is not blocked.
+  changelog:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - name: Require a CHANGELOG entry for the crate version on main
+        shell: bash
+        run: |
+          set -euo pipefail
+          version=$(grep -m1 '^version = ' Cargo.toml | sed -E 's/.*"([^"]+)".*/\1/')
+          if grep -qE "^## \[${version}\]" CHANGELOG.md; then
+            echo "CHANGELOG.md has an entry for ${version}."
+            exit 0
+          fi
+          msg="CHANGELOG.md has no '## [${version}]' entry"
+          if [ "${GITHUB_REF_NAME:-}" = "main" ] || [ "${GITHUB_BASE_REF:-}" = "main" ]; then
+            echo "::error::${msg} — main requires a changelog entry for the released version."
+            exit 1
+          fi
+          echo "::warning::${msg} (allowed on ${GITHUB_REF_NAME:-unknown}; required before it can reach main)."
+
   lint:
+    needs: resolve-msrv
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
@@ -31,25 +77,37 @@ jobs:
           repository: freemkv/freemkv-unlock
           ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
-      - uses: dtolnay/rust-toolchain@1.97.0
+      # fmt runs on the pinned MSRV toolchain; clippy runs on stable. Third
+      # parties compile our source on their own toolchain and never run our
+      # clippy, so the lint toolchain need not match the MSRV — only build/test
+      # must (see the test/cross jobs). Linting on stable makes new-lint debt a
+      # BLOCKING gate the pinned version would otherwise hide. The MSRV pin is
+      # installed second so it stays the default toolchain (fmt uses it
+      # implicitly); clippy is invoked explicitly with `+stable`.
+      - uses: dtolnay/rust-toolchain@stable
         with:
-          components: clippy, rustfmt
+          components: clippy
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
+          components: rustfmt
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: libfreemkv
       - run: cargo fmt --check
         working-directory: libfreemkv
-      # libfreemkv is a library — Cargo.lock is gitignored. --locked
-      # would always fail on a fresh runner because there's no committed
-      # lockfile to lock against. The binary crates (freemkv, autorip,
-      # bdemu) track Cargo.lock and DO use --locked.
+      # Cargo.lock is now committed (issue #15) and the `deny` job audits the
+      # resolved graph, but --locked is still omitted: CI's sibling path-patch
+      # layout resolves the freemkv crates as path packages, which --locked
+      # can't satisfy — the same reason the binary crates omit it in ci.yml.
       # --all-targets so TEST code is linted too. Without it this crate — the
       # reference implementation for the other seven — was the only one whose
       # tests had never been linted at all, and it was hiding 74 findings.
-      - run: cargo clippy --all-targets -- -D warnings
+      - run: cargo +stable clippy --all-targets -- -D warnings
         working-directory: libfreemkv
 
   test:
+    needs: resolve-msrv
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
@@ -69,13 +127,84 @@ jobs:
           repository: freemkv/freemkv-unlock
           ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: libfreemkv
       - run: cargo test --tests
         working-directory: libfreemkv
 
+  # The memory orderings in `scsi::fd_handoff` — the fd hand-off between a
+  # recovery thread and `SgIoTransport::drop` — cannot be checked by `cargo
+  # test`: they compile to the same instructions on x86_64, so the WRONG ones
+  # pass every run. loom enumerates the executions the C++20 model permits and
+  # reports the leaked descriptor directly, which makes it the only regression
+  # coverage that part of the module has. If this job stops running, that
+  # coverage disappears silently behind a green build.
+  #
+  # Its own job rather than a step in `test` because `RUSTFLAGS` is part of the
+  # rust-cache key: folding it into `test` costs that job a full cache miss on
+  # every run. It takes the same sibling checkout as the jobs above even though
+  # `--no-default-features` drops freemkv-unlock from the BUILD — `--features`
+  # does not exempt an optional path dependency from manifest RESOLUTION, so
+  # without the sibling this job would fail the moment the branch tip carries
+  # the path-dep form of that dependency rather than a git tag.
+  loom:
+    needs: resolve-msrv
+    runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: --cfg loom
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          path: libfreemkv
+      - uses: actions/checkout@v7
+        with:
+          repository: freemkv/freemkv-unlock
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
+          path: freemkv-unlock
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
+          components: clippy
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: libfreemkv
+      - run: cargo test --lib --no-default-features --features scsi fd_handoff
+        working-directory: libfreemkv
+      # `lint` runs clippy without `--cfg loom`, so this is the only place the
+      # model code is linted at all.
+      - run: cargo clippy --lib --no-default-features --features scsi --profile test -- -D warnings
+        working-directory: libfreemkv
+
+  deny:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          path: libfreemkv
+      # libfreemkv path-deps ../freemkv-unlock on the BRANCH tip (release.sh
+      # swaps it to a git tag only inside the tagged commit, then restores the
+      # path dep). CI checks out one repo, so the branch tip has never been
+      # buildable here — every green run you have ever seen was a tag build,
+      # and Windows/Linux were first compiled at release time.
+      #
+      # Both repos go into subdirectories because actions/checkout refuses a
+      # `path:` outside $GITHUB_WORKSPACE, and `../freemkv-unlock` is outside.
+      # With this layout the path dep resolves exactly as it does locally.
+      - uses: actions/checkout@v7
+        with:
+          repository: freemkv/freemkv-unlock
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
+          path: freemkv-unlock
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: EmbarkStudios/cargo-deny-action@v2
+        with:
+          command: check advisories bans licenses sources
+          manifest-path: libfreemkv/Cargo.toml
+
   check-macos:
     # dev is the FAST lane: this job still runs, but on the release-candidate
     # branches rather than on every push to dev. Nothing is deleted and no
@@ -89,6 +218,7 @@ jobs:
     # than a slow one: release.sh's CI gate refuses while any run for the
     # commit is still in progress, so a never-scheduled job blocks releases
     # silently -- see the note on real-media in qa.yml.
+    needs: resolve-msrv
     if: github.ref_name == 'qa' || github.ref_name == 'main'
     runs-on: macos-latest
     steps:
@@ -109,7 +239,9 @@ jobs:
           repository: freemkv/freemkv-unlock
           ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: libfreemkv
@@ -129,6 +261,7 @@ jobs:
     # than a slow one: release.sh's CI gate refuses while any run for the
     # commit is still in progress, so a never-scheduled job blocks releases
     # silently -- see the note on real-media in qa.yml.
+    needs: resolve-msrv
     if: github.ref_name == 'qa' || github.ref_name == 'main'
     runs-on: windows-latest
     steps:
@@ -149,7 +282,9 @@ jobs:
           repository: freemkv/freemkv-unlock
           ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
           path: freemkv-unlock
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: libfreemkv
@@ -204,7 +339,11 @@ jobs:
           freemkv-i18n = { path = "../freemkv-i18n" }
           EOF
           done
-      - uses: dtolnay/rust-toolchain@1.97.0
+      # The dependents span a higher MSRV than libfreemkv itself — the binaries
+      # (freemkv/autorip/bdemu) always track the highest supported Rust. Build
+      # them on `stable` so this job satisfies the highest dependent floor; the
+      # library's own lower MSRV (verified by the `test` job) cannot compile them.
+      - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: |
@@ -227,3 +366,43 @@ jobs:
         working-directory: autorip
       - run: cargo test --tests
         working-directory: bdemu
+
+  # ── Coverage (non-required, additive) ───────────────────────────────────────
+  #
+  # Reports line coverage to Codecov. Deliberately NOT wired into any release
+  # gate: it is informational only (see codecov.yml) and no other job `needs:`
+  # it. Mirrors the `test` job's layout exactly — same MSRV toolchain (resolved
+  # from Cargo.toml), same dual checkout so `../freemkv-unlock` resolves, cache
+  # workspace and working-directory. cargo-llvm-cov comes as a prebuilt binary
+  # from taiki-e/install-action, so it is toolchain-independent.
+  #
+  # No `--locked`: like the fmt/clippy/test jobs above, the sibling path-patch
+  # layout resolves the freemkv crates as path packages, which --locked can't satisfy.
+  coverage:
+    needs: resolve-msrv
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          path: libfreemkv
+      - uses: actions/checkout@v7
+        with:
+          repository: freemkv/freemkv-unlock
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
+          path: freemkv-unlock
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
+          components: llvm-tools-preview
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: libfreemkv
+      - uses: taiki-e/install-action@cargo-llvm-cov
+      - run: cargo llvm-cov --workspace --ignore-run-fail --lcov --output-path lcov.info
+        working-directory: libfreemkv
+      - uses: codecov/codecov-action@v7
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          files: libfreemkv/lcov.info
+          slug: freemkv/libfreemkv
+          fail_ci_if_error: false

.github/workflows/comment-guard.yml

@@ -0,0 +1,17 @@
+name: comment-guard
+
+# Caps explanatory prose by COMMENT INTENT (not visibility):
+#   //! / /*! module docs  — unbounded (module-scoped, can't hide per-item text)
+#   ///  / /** */ item docs — 8 prose lines (fenced ``` examples excluded)
+#   //   / /* */  asides    — 3 lines (single-blank-separated runs count as one)
+# Overflow belongs in the module //! or docs/<topic>.md with a one-line // pointer.
+
+on: [push, pull_request]
+
+jobs:
+  comment-guard:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - name: Run comment-guard
+        run: python3 ci/comment-guard.py

.github/workflows/doc-links.yml

@@ -0,0 +1,32 @@
+name: doc-links
+
+# Fails on broken intra-doc links in `///`/`//!` doc comments (e.g. a `[Type]`
+# link to a renamed/removed item). Catches doc drift that `cargo build` misses.
+#
+# libfreemkv path-deps ../freemkv-unlock on the branch tip, so — like ci.yml —
+# both repos are checked out into sibling subdirectories for the path dep to
+# resolve.
+
+on: [push, pull_request]
+
+jobs:
+  doc-links:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          path: libfreemkv
+      - uses: actions/checkout@v7
+        with:
+          repository: freemkv/freemkv-unlock
+          ref: "${{ github.ref_name == 'qa' && 'qa' || 'dev' }}"
+          path: freemkv-unlock
+      - uses: dtolnay/rust-toolchain@1.98.0
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: libfreemkv
+      - name: cargo doc (deny broken intra-doc links)
+        working-directory: libfreemkv
+        env:
+          RUSTDOCFLAGS: "-D rustdoc::broken_intra_doc_links"
+        run: cargo doc --no-deps --document-private-items --lib --bins

.github/workflows/identity-guard.yml

@@ -0,0 +1,41 @@
+name: identity-guard
+# Prevention: no commit may carry an unrelated-business or non-canonical author/
+# committer email. dev@example.com (a dead corp address) once slipped onto the
+# release cascade + a batch of local commits; this fails the build if it recurs.
+on:
+  push:
+    branches: [dev, qa, main]
+  pull_request:
+jobs:
+  identity:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+      - name: Reject banned author/committer emails
+        env:
+          BEFORE: ${{ github.event.before }}
+          AFTER: ${{ github.sha }}
+          EVENT: ${{ github.event_name }}
+          PR_BASE: ${{ github.event.pull_request.base.sha }}
+          PR_HEAD: ${{ github.event.pull_request.head.sha }}
+        run: |
+          set -euo pipefail
+          # Unrelated business domains + a personal address normalized to the
+          # GitHub noreply. Real external contributors are unaffected.
+          BANNED='@example-a\.invalid|@example-b\.invalid|owner@example\.invalid'
+          if [ "$EVENT" = "pull_request" ]; then
+            range="$PR_BASE..$PR_HEAD"
+          elif [ -n "${BEFORE:-}" ] && [ "$BEFORE" != "0000000000000000000000000000000000000000" ] && git cat-file -e "$BEFORE" 2>/dev/null; then
+            range="$BEFORE..$AFTER"
+          else
+            range="$AFTER~1..$AFTER"
+          fi
+          bad=$(git log --format='%an <%ae>%n%cn <%ce>' "$range" 2>/dev/null | sort -u | grep -iE "$BANNED" || true)
+          if [ -n "$bad" ]; then
+            echo "::error::commit(s) carry a banned author/committer identity:"; echo "$bad" | sed 's/^/  /'
+            echo "::error::Commit as your GitHub noreply (1085847+MattJackson@users.noreply.github.com). Fix: git config user.email <noreply>; git commit --amend --reset-author."
+            exit 1
+          fi
+          echo "identity-guard: clean"

.github/workflows/qa.yml

@@ -24,6 +24,19 @@ on:
   workflow_dispatch:
 
 jobs:
+  # Single source of truth for the MSRV — see ci.yml. Jobs that build/test AT
+  # the MSRV read `needs.resolve-msrv.outputs.v` from Cargo.toml's rust-version;
+  # clippy (cross-lint) runs on stable instead.
+  resolve-msrv:
+    runs-on: ubuntu-latest
+    outputs:
+      v: ${{ steps.msrv.outputs.v }}
+    steps:
+      - uses: actions/checkout@v7
+      - id: msrv
+        shell: bash
+        run: echo "v=$(grep -m1 '^rust-version' Cargo.toml | sed -E 's/.*\"([^\"]+)\".*/\1/')" >> "$GITHUB_OUTPUT"
+
   # ── Name the candidate ────────────────────────────────────────────────
   #
   # Every push to `qa` is a release candidate, so every push gets a tag:
@@ -65,6 +78,7 @@ jobs:
   # changes what the optimiser can prove. A test that only passes in debug is
   # a test that never guarded the binary anyone actually ships.
   release-tests:
+    needs: resolve-msrv
     strategy:
       fail-fast: false
       matrix:
@@ -79,7 +93,9 @@ jobs:
           repository: freemkv/freemkv-unlock
           ref: qa
           path: freemkv-unlock
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: libfreemkv
@@ -100,7 +116,9 @@ jobs:
           repository: freemkv/freemkv-unlock
           ref: qa
           path: freemkv-unlock
-      - uses: dtolnay/rust-toolchain@1.97.0
+      # clippy runs on stable (matches ci.yml's lint job); build/test stay on
+      # the MSRV pin. See ci.yml for why the lint toolchain need not be the MSRV.
+      - uses: dtolnay/rust-toolchain@stable
         with:
           components: clippy
       - uses: Swatinem/rust-cache@v2
@@ -115,6 +133,7 @@ jobs:
   # of the SCSI transport and platform layers compile on no other runner, so
   # without this they are first built at release time.
   windows-build:
+    needs: resolve-msrv
     runs-on: windows-latest
     steps:
       - uses: actions/checkout@v7
@@ -125,7 +144,9 @@ jobs:
           repository: freemkv/freemkv-unlock
           ref: qa
           path: freemkv-unlock
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ needs.resolve-msrv.outputs.v }}
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: libfreemkv

.github/workflows/release.yml

@@ -29,7 +29,7 @@ jobs:
 
   # Tests run as a PARALLEL TRIPWIRE: they fail the run if they fail, but the
   # publish/release jobs do NOT `needs:` this job. The tag decision was already
-  # gated by the local precommit (same Rust 1.97, same commit). Binary consumers
+  # gated by the local precommit (same MSRV, same commit). Binary consumers
   # (freemkv/autorip/bdemu) git-tag-pin libfreemkv and therefore start building
   # the instant this tag exists — so this test job and the crates.io publish
   # below must NOT sit on their critical path.
@@ -38,10 +38,16 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - id: msrv
+        shell: bash
+        run: echo "v=$(grep -m1 '^rust-version' Cargo.toml | sed -E 's/.*\"([^\"]+)\".*/\1/')" >> "$GITHUB_OUTPUT"
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ steps.msrv.outputs.v }}
       - uses: Swatinem/rust-cache@v2
-      # libfreemkv is a library — Cargo.lock isn't tracked, so --locked
-      # would always fail (no lockfile to lock against on a fresh runner).
+      # Cargo.lock is now committed (issue #15), but --locked is still omitted:
+      # the sibling path-patch layout resolves the freemkv crates as path
+      # packages, which --locked can't satisfy.
       - run: cargo test
 
   # NOTE: there is no crates.io publish job. libfreemkv is git-tag-only

.gitignore

@@ -1,5 +1,4 @@
 /target
-Cargo.lock
 *.swp
 *.swo
 .DS_Store

CHANGELOG.md

@@ -1,5 +1,124 @@
 # Changelog
 
+## [1.7.0] — 2026-09-02
+
+### Fixed
+
+- `mux/mp4`: the capped child-box scan treated any `size < 8` as a stop, which dropped a 64-bit `largesize` child box (`size == 1`, real length in the following 8 bytes) and every sibling after it; a `size == 0` (run-to-end) box was mishandled too. Both are now honoured, so an MP4/MOV whose boxes use 64-bit sizes is walked fully instead of truncated.
+
+- Linux: `SgIoTransport::raw_command` clamped an over-length CDB with `cdb.len().min(16)` instead of routing it through the shared `checked_cdb_len` guard that `execute()` uses. Under SPC-4 a CDB's length is fixed by its opcode, so truncating one does not shorten the command — it sends a descriptor the drive will read as something else. An empty CDB was likewise unguarded, and went to the sg driver as a zero-length command descriptor. Unreachable — `raw_command` is private and its one caller passes a fixed 6-byte ALLOW MEDIUM REMOVAL — but it was the one transport path that did the thing the guard exists to prevent.
+- Linux: the fd hand-off between a background recovery thread and `SgIoTransport::drop` had no release edge, so a recovery thread that published its fd after teardown had drained the slot was not guaranteed to observe `dead == true` and could leave the descriptor unclosed. `Drop`'s claiming `swap` was `Acquire` (a relaxed store, heading no release sequence) and the recovery thread's `compare_exchange` was `Release` (a relaxed load, acquiring nothing) — neither side alone was enough, and upgrading only one still leaks. Both are now `AcqRel`. Worst case was a leaked file descriptor on a transport already being torn down.
+
+- Windows: `scsi::windows::list_drives` reached into the `rip`-gated `drive`/`identity` modules, so a scsi-only consumer (`default-features = false, features = ["scsi"]`) failed to compile — `--all-features` CI never exercised that combination. It now enumerates directly via `scsi::open` + `scsi::inquiry`, like the Linux and macOS backends. Surfaced by freemkv-firmware, which links libfreemkv scsi-only.
+
+### Changed
+
+- The Linux recovery-thread fd hand-off moved to `scsi::fd_handoff`, where it is compiled and unit-tested on every platform (`linux.rs` is built on one host only) and model-checked under `loom`. No public API change.
+
+### Security
+
+- Fixed a soundness bug (GHSA-j8ww-f5fg-9pmh, low severity): `PrefetchedSectorSource::into_channels` handed out a `Sender<Vec<u8>>` recycle channel whose buffers the producer re-exposed with `unsafe { Vec::set_len }` guarded only by capacity, so a downstream caller recycling a `Vec::with_capacity(n)` (len 0) could drive `set_len` over uninitialized memory — undefined behaviour reachable from safe code. The producer now uses `Vec::resize`, removing the `unsafe`; buffer pooling (the real cross-thread alloc/free win) is unchanged. No in-tree caller triggered it.
+
+## [1.6.14] — 2026-08-31
+
+### Changed
+
+- Version aligned to 1.6.14 for the unified release.
+
+## [1.6.13] — 2026-08-28
+
+### Added
+
+- Capture a few additional drive buffers during `info --share` collection on supported drives.
+
+## [1.6.12] — 2026-08-27
+
+### Fixed
+
+- macOS: hold a DiskArbitration claim (plus a mount-approval dissenter) for the SCSI transport's lifetime so `diskarbitrationd` can't remount the disc mid-rip — the cause of the E1000 "disc stolen mid-rip" failure on macOS.
+
+### Changed
+
+- Comment and documentation cleanup.
+
+## [1.6.11] — 2026-08-26
+
+### Added
+
+- Navigation-driven main-feature selection: selection now follows the disc's
+  own on-disc menu/navigation logic — a Blu-ray HDMV navigation VM and a DVD
+  First-Play resolver — to reach the main feature, instead of guessing by
+  title size alone.
+- Clip-set composite/decoy detection, so a title assembled from a composite
+  or decoy clip set is recognized as such during selection.
+- A feature-payload floor, giving main-feature selection a minimum-size
+  sanity check.
+- Normalized `DiscProfile` output.
+- Vendor navigation-label parsing.
+- Substantially expanded unit-test coverage across the navigation and
+  clip-selection paths.
+
+### Fixed
+
+- Main-feature selection no longer picks an obfuscated decoy playlist over
+  the real feature.
+- Two rounds of code-audit hardening: navigation VM operand/field-offset
+  conformance, navigation now abstains rather than guessing on an
+  undecidable system-parameter branch, panic-safety fixes, log-escaping
+  fixes, and expanded fuzz/test coverage.
+- Direct disc reads (`disc://…`): `DiscStream` now threads a cumulative feed
+  base offset into the demuxer (`feed_at`) for both the TS and PS paths and
+  forwards it onto each `PesPacket`, so demuxed frames carry byte-exact source
+  provenance (`SourcePos`). Without it, `SeamPlan::place` fell back to a PTS
+  heuristic that a B-frame PTS reorder dip could misread as a `stepped_back`
+  clip transition, dropping all subsequent video frames in multi-clip playlists.
+
+### Changed
+
+- Lowered the minimum supported Rust version (MSRV) from 1.97 to 1.94. This is
+  the lowest toolchain on which `cargo build`, `cargo clippy --all-targets
+  -D warnings`, and `cargo test --tests` all pass clean; CI toolchain pins were
+  moved to match. (The crate's dependencies floor `cargo build` at 1.90, but
+  clippy is only warning-clean from 1.94.)
+
+## [1.6.10] — 2026-08-23
+
+### Fixed
+
+- TrueHD/MLP audio: on a source transport-stream discontinuity (lost or gapped
+  packets, signalled by a continuity-counter break), the parser now drops forward
+  to the next major-sync access unit before resuming, instead of splicing the
+  post-gap audio mid-stream. MLP carries predictor + restart state across access
+  units, so resuming mid-stream decoded against stale state and produced a
+  decoder-choking seam — streaming decoders emitted a burst of "restart header
+  sync incorrect" / "Invalid blocksize" errors and could flag the whole track
+  corrupt. This mirrors the video path (resync to the next keyframe after a gap)
+  and how the independent-frame audio codecs (AC-3, DTS, FLAC, AAC) already
+  recover; the fix is guarded so it never arms before a validated major-sync
+  baseline exists (no whole-track drop at stream head). The gapped instant itself
+  is in the source and cannot be recovered, but the muxed track is now
+  decoder-clean.
+
+## [1.6.9] — 2026-08-22
+
+### Changed
+
+- Version aligned to 1.6.9 for the unified release. No functional changes to
+  this crate; the release was driven by autorip (automatic per-episode TV
+  ripping — each episode named `S{NN}E{MM}`, with TMDB runtime-aligned episode
+  numbering across multi-disc seasons — a Manual Rename option, and a unified
+  per-disc staging state file — see the autorip 1.6.9 notes).
+
+## [1.6.8] — 2026-08-21
+
+### Changed
+
+- Version aligned to 1.6.8 for the unified release. No functional changes to
+  this crate; the release was driven by autorip (webhooks now fire per pipeline
+  stage — Rip / Mux / Move — with the Rip hook firing the moment the drive is
+  free again, plus a Ripper-tab activity-banner fix so it also shows during
+  moves — see the autorip 1.6.8 notes).
+
 ## [1.6.7] — 2026-08-21
 
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+dependencies = [
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+ "crc32fast",
+ "log",
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+]
+
+[[patch.unused]]
+name = "freemkv-engine"
+version = "1.7.0"
+
+[[patch.unused]]
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+version = "1.7.0"
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+name = "freemkv-keysources"
+version = "1.7.0"

Cargo.toml

@@ -1,8 +1,8 @@
 [package]
 name = "libfreemkv"
-version = "1.6.7"
+version = "1.7.1"
 edition = "2024"
-rust-version = "1.97"
+rust-version = "1.88"
 license = "MIT"
 description = "Open source raw disc access library for optical drives"
 repository = "https://github.com/freemkv/libfreemkv"
@@ -18,45 +18,79 @@ publish = false
 lto = "thin"
 codegen-units = 1
 
+# ── Feature layout ───────────────────────────────────────────────────────────
+# `scsi`  — the SCSI passthrough transport layer ONLY (`src/scsi/` + `error`):
+#           ScsiTransport/execute, ScsiResult/ScsiSense/parse_sense, DriveInfo,
+#           list_drives, drive_has_disc, CDB builders, the per-OS backends and
+#           the raw-`cc` macOS shim (built by build.rs). Pulls only `tracing`
+#           (transport instrumentation) plus the always-on `libc` target dep —
+#           none of the ripping dependency tree.
+# `rip`   — the full ripping tree (drive lifecycle, disc/UDF/MPLS/CLPI parsing,
+#           AACS/CSS decrypt, PES/mux pipeline, keydb, freemkv-unlock seam). All
+#           heavy deps (serde, zip, rayon, roxmltree, rand, crossbeam, memchr,
+#           sha1, aes, base64, freemkv-unlock, serde_json) live here.
+# `default = ["rip", "scsi"]` preserves today's full build byte-for-byte;
+# consumers wanting transport only use `default-features = false, features =
+# ["scsi"]`. `rip` implies `scsi` because the ripping tree reads through it.
+[features]
+default = ["rip", "scsi"]
+scsi = ["dep:tracing"]
+rip = [
+    "scsi",
+    "dep:serde",
+    "dep:serde_json",
+    "dep:sha1",
+    "dep:aes",
+    "dep:freemkv-unlock",
+    "dep:rand",
+    "dep:zip",
+    "dep:base64",
+    "dep:roxmltree",
+    "dep:crossbeam-channel",
+    "dep:rayon",
+    "dep:memchr",
+]
+
 [dependencies]
-serde = { version = "1", features = ["derive"] }
-serde_json = "1"
-sha1 = "0.10"
-aes = "0.9"
+serde = { version = "1", features = ["derive"], optional = true }
+serde_json = { version = "1", optional = true }
+sha1 = { version = "0.10", optional = true }
+aes = { version = "0.9", optional = true }
 # Interim path dep for local cross-repo dev; the release script re-pins this to
 # `{ git = ".../freemkv-unlock", tag = "vX.Y.Z" }` before tagging libfreemkv (so
 # the released tag resolves freemkv-unlock from git, not a sibling path).
-freemkv-unlock = { git = "https://github.com/freemkv/freemkv-unlock", tag = "v1.6.7" }
-rand = "0.10"
-zip = { version = "8", default-features = false, features = ["deflate"] }
-base64 = "0.23"
+freemkv-unlock = { path = "../freemkv-unlock", optional = true }
+rand = { version = "0.10", optional = true }
+zip = { version = "8", default-features = false, features = ["deflate"], optional = true }
+base64 = { version = "0.23", optional = true }
 # Read-only XML DOM parser (pure Rust, forbid(unsafe_code), entity-expansion
 # bounded). Parses the HD-DVD Advanced-Content playlist `ADV_OBJ/VPLST000.XPL`
 # — untrusted disc bytes — into authoritative titles/clips/chapters. A real
 # parser, not a hand-rolled scanner: the XPL is genuine XML (comments, varied
 # attribute order, self-closing tags).
-roxmltree = "0.20"
+roxmltree = { version = "0.20", optional = true }
 # Trace-level instrumentation for the read/transport path (SgIoTransport::execute
-# and friends). Permitted
+# and friends). Part of the `scsi` feature — the transport layer traces here.
+# Permitted
 # under CLAUDE.md ("Acceptable strings: debug/trace logging"). Consumers (autorip)
 # wire a tracing subscriber and pipe events into the JSONL debug log.
-tracing = "0.1"
+tracing = { version = "0.1", optional = true }
 # Bounded MPSC channel with kernel-wakeup send_timeout. Used by `io::pipeline`
 # so the halt-aware send/finish loops can BLOCK on consumer drain instead of
 # polling — the 50 ms poll cadence of the previous mpsc-based impl capped mux
 # throughput at ~1 MB/s (0.21.7).
-crossbeam-channel = "0.5"
+crossbeam-channel = { version = "0.5", optional = true }
 # Persistent work-stealing thread pool for parallel AACS unit
 # decryption. Per-call std::thread::scope spawned fresh OS threads
 # and that overhead dominated for typical batch sizes (60 units).
 # rayon's global pool initialises once on first use.
-rayon = "1"
+rayon = { version = "1", optional = true }
 # SIMD-accelerated bytestring search. Drives the HEVC/H.264 start-code
 # scan in `mux::codec::h264::find_start_code` — naive byte-by-byte
 # walk is ~500 MB/s single-thread on x86_64; memchr's vectorised
 # `memmem::find` for the 3-byte `00 00 01` needle hits ~5 GB/s on
 # AVX2-capable hosts.
-memchr = "2"
+memchr = { version = "2", optional = true }
 
 [target.'cfg(target_os = "linux")'.dependencies]
 libc = "0.2"
@@ -67,7 +101,35 @@ libc = "0.2"
 [dev-dependencies]
 tempfile = "3"
 
+# Permutation model checker for the `scsi::fd_handoff` atomics — the fd
+# hand-off between a Linux recovery thread and `SgIoTransport::drop`. A normal
+# test cannot see a missing release edge there: the orderings compile to the
+# same instructions on x86_64, so the wrong ones pass every time. loom
+# enumerates the executions the C++20 model permits and reports the leaked
+# descriptor directly.
+#
+# Behind `cfg(loom)`, which nothing sets unless you ask for it, so this is out
+# of the graph for every ordinary build and for every CI job but the dedicated
+# `loom` one. Run it with:
+#
+#     RUSTFLAGS="--cfg loom" cargo test --lib --no-default-features \
+#         --features scsi fd_handoff
+#
+# `cargo test --lib` specifically: as a DEV-dependency loom is only in scope for
+# test targets, which is why `fd_handoff` gates its import on `all(loom, test)`
+# and falls back to std elsewhere. Without that, `--cfg loom` would break plain
+# `cargo build`/`clippy` with an unresolved-crate error.
+[target.'cfg(loom)'.dev-dependencies]
+loom = "0.7"
+
 [[bench]]
 name = "sgio_read"
 harness = false
 
+
+[lints.rust]
+# `loom` is set by RUSTFLAGS for the model checker above, never by a feature.
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(loom)'] }
+
+[lints.clippy]
+uninlined_format_args = "allow"

Makefile

@@ -1,7 +1,7 @@
 # libfreemkv — local dev helper.
 # Mirrors the workspace-wide CI checks but scoped to this single crate.
 
-.PHONY: test build check ci clean
+.PHONY: test build check loom ci clean
 
 test:
 	cargo test --tests
@@ -13,7 +13,13 @@ check:
 	cargo fmt --check
 	cargo clippy --all-targets -- -D warnings
 
-ci: check build test
+# Model-check the scsi::fd_handoff atomics. `cargo test` cannot fail on those
+# orderings — they compile to the same instructions on x86_64 — so this is the
+# only check on them. Mirrors the `loom` CI job.
+loom:
+	RUSTFLAGS="--cfg loom" cargo test --lib --no-default-features --features scsi fd_handoff
+
+ci: check build test loom
 
 clean:
 	cargo clean

README.md

@@ -1,10 +1,14 @@
+[![Sponsor](https://img.shields.io/badge/Sponsor-%E2%9D%A4-ea4aaa?logo=github-sponsors)](https://github.com/sponsors/MattJackson)
+
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue)](LICENSE)
+[![CI](https://github.com/freemkv/libfreemkv/actions/workflows/ci.yml/badge.svg)](https://github.com/freemkv/libfreemkv/actions/workflows/ci.yml)
+[![codecov](https://codecov.io/gh/freemkv/libfreemkv/branch/dev/graph/badge.svg)](https://codecov.io/gh/freemkv/libfreemkv)
 
 # libfreemkv
 
-Rust library for 4K UHD / Blu-ray / DVD optical drives. Drive access, disc scanning, stream labels, AACS decryption, CSS decryption, KEYDB updates, and content reading in one crate. Drive-level unlocking is handled internally; consumers work with disc access and decryption only.
+Rust library for 4K UHD / Blu-ray / DVD optical drives. Drive access, disc scanning, stream labels, AACS decryption, CSS decryption, and content reading in one crate. Drive-level unlocking is handled internally; consumers work with disc access and decryption only.
 
-DVDs (CSS) decrypt out of the box. Blu-ray and UHD (AACS) require a `keydb.cfg` (default `~/.config/freemkv/keydb.cfg`) supplying disc-specific volume unique keys; no AACS key material is compiled in.
+DVDs (CSS) decrypt out of the box. Blu-ray and UHD (AACS) require disc-specific volume unique keys, supplied by the consumer (e.g. via [freemkv-keysources](https://github.com/freemkv/freemkv-keysources), which owns `keydb.cfg` lookup/download); libfreemkv itself never reads `keydb.cfg` or downloads keys, and no AACS key material is compiled in.
 
 **12+ MB/s** sustained read speeds on BD. Drive prep (`init()`) handles unlocking internally via the `freemkv-unlock` crate — clients never see it; when no drive unlock applies, the library rips via the host-certificate AACS handshake.
 
@@ -70,9 +74,8 @@ cannot call into it; front-ends get recovery from the engine directly. See
 - **Drive access** — open, identify, internal unlock + prep, speed control, eject
 - **12+ MB/s reads** — auto-detects kernel transfer limits, sustained full speed
 - **Disc scanning** — UDF 2.50 filesystem, MPLS playlists, CLPI clip info
-- **Stream labels** — 5 BD-J format parsers (Paramount, Criterion, Pixelogic, CTRM, Deluxe)
+- **Stream labels** — 7 BD-J format parsers (Paramount, Criterion, Pixelogic, CTRM, DBP, Deluxe, Fox)
 - **AACS decryption** — transparent key resolution and content decrypt (1.0 + 2.0 bus decryption)
-- **KEYDB updates** — download, verify, save from any HTTP URL (zero deps, raw TCP)
 - **Content reading** — adaptive batch reads with automatic decryption
 - **Stream I/O** — unified stream pipeline for reading and writing any format
 
@@ -94,7 +97,7 @@ Streams implement a single unified `pes::Stream` trait (re-exported as `PesStrea
 
 DVDs (CSS) decrypt out of the box, with no external key file needed.
 
-Blu-rays and UHD (AACS) require a `keydb.cfg` at `~/.config/freemkv/keydb.cfg` (or passed via `ScanOptions`). No AACS key material is compiled into the binary.
+Blu-rays and UHD (AACS) require Unit Keys passed in via `ScanOptions`/`KeySpec`. libfreemkv does not read `keydb.cfg` or fetch keys itself — that's the consumer's job (see [freemkv-keysources](https://github.com/freemkv/freemkv-keysources)). No AACS key material is compiled into the binary.
 
 ## Architecture
 
@@ -109,10 +112,9 @@ Disc                   — scan titles, streams, AACS/CSS state
   ├── MPLS parser      — playlists → titles + clips + streams
   ├── CLPI parser      — clip info → EP map → sector extents
   ├── IFO parser       — DVD title sets, PGC chains, cell addresses
-  ├── Labels           — 5 BD-J format parsers (detect + parse)
+  ├── Labels           — 7 BD-J format parsers (detect + parse)
   ├── AACS             — key resolution + content decryption
-  ├── CSS              — DVD CSS (bus auth → player-key disc crack → known-plaintext title-key attack)
-  └── KEYDB            — download + verify + save
+  └── CSS              — DVD CSS (bus auth → player-key disc crack → known-plaintext title-key attack)
 
 Streams                — unified PES pipeline
   ├── PesStream        — pes::Stream: one trait, read()/write() PES frames

build.rs

@@ -5,6 +5,7 @@ fn main() {
     if target == "macos" {
         println!("cargo:rustc-link-lib=framework=IOKit");
         println!("cargo:rustc-link-lib=framework=CoreFoundation");
+        println!("cargo:rustc-link-lib=framework=DiskArbitration");
 
         let out_dir = std::env::var("OUT_DIR").unwrap();
         let obj = format!("{out_dir}/macos_shim.o");

ci/comment-guard.py

@@ -0,0 +1,252 @@
+#!/usr/bin/env python3
+"""comment-guard: cap explanatory prose by COMMENT INTENT, not visibility.
+
+Three tiers, keyed on the syntax the author reached for:
+
+  * `//!` / `/*!` — a module (or crate) design doc. UNBOUNDED. There is one per
+    file, at the top, documenting the module as a whole, so it can't be used to
+    smuggle per-item rationale the way item docs can. Long correctness / design
+    essays (e.g. a memory-ordering proof) legitimately live here.
+  * `///` / `/** */` — item documentation. Up to DOC_CAP *prose* lines. Fenced
+    ``` code blocks do NOT count, so real examples aren't punished. This holds
+    whether or not the item is `pub`: a `pub(crate)` fn deserves a real doc
+    paragraph just like a `pub` one. Capping `///` here (rather than exempting
+    it, as the old guard did — issue #17) is what stops rationale being hidden
+    behind a doc sigil, while still leaving room for a genuine paragraph.
+  * `//` / `/* */` — a quick internal aside. Up to INLINE_CAP lines. This is the
+    shape that sprawls into walls, so it's kept tight: stanzas separated by a
+    single blank line count CUMULATIVELY, so one essay can't be split into runs.
+
+Overflow belongs in the module `//!`, or in docs/<topic>.md with a one-line `//`
+pointer — both show up in review.
+
+Scans src/ and tests/ under the given root (default cwd). `--selftest` runs
+built-in cases. Exit non-zero if any block exceeds its cap.
+"""
+import re
+import sys
+from pathlib import Path
+
+INLINE_CAP = 3
+DOC_CAP = 8
+
+_RAW_OPEN = re.compile(r'r(#*)"')  # raw string opener: r"…", r#"…"#, br##"…"## …
+
+
+def _strip_line_comment(s):
+    """Return (kind, body) for a whole-line comment, else (None, None).
+
+    kind is 'doc' for `///`/`//!`, 'plain' for other `//`. A trailing comment on
+    a code line is not a whole-line comment and is ignored (single-line, cheap).
+    """
+    if s.startswith("//!"):
+        return "doc", s[3:]
+    if s.startswith("///") and not s.startswith("////"):
+        return "doc", s[3:]
+    if s.startswith("//"):
+        return "plain", s[2:]
+    return None, None
+
+
+def _fence_toggle(body):
+    """True if this doc body line opens/closes a ``` fenced code block."""
+    return body.strip().startswith("```")
+
+
+def _classify(lines):
+    """Yield per-line dicts: comment kind ('doc'/'plain'/None), doc-ness of
+    block comments, and code info. Block comments are tracked across lines.
+    """
+    info = []
+    in_block = False
+    block_is_doc = False
+    raw_hashes = None  # None = not in a raw string; int N = open, needs '"' + N*'#'
+    for raw in lines:
+        s = raw.lstrip()
+        rec = {"raw": raw, "s": s, "comment": None, "is_doc": False, "code": False}
+        # Inside a raw string literal (e.g. an embedded HTML/CSS/JS asset): the
+        # bytes are string data, not Rust comments, so the guard is blind to them
+        # until the string closes. Prevents `/* */` or `//` lines in an embedded
+        # page from being counted as comment blocks.
+        if raw_hashes is not None:
+            if ('"' + "#" * raw_hashes) in raw:
+                raw_hashes = None
+            info.append(rec)
+            continue
+        if in_block:
+            rec["comment"] = "doc" if block_is_doc else "plain"
+            rec["is_doc"] = block_is_doc
+            if "*/" in raw:
+                in_block = False
+            info.append(rec)
+            continue
+        # A block comment only starts a comment-line if it's the first token.
+        if s.startswith("/*"):
+            rec["is_doc"] = s.startswith("/**") or s.startswith("/*!")
+            rec["comment"] = "doc" if rec["is_doc"] else "plain"
+            if "*/" not in s[2:]:
+                in_block = True
+                block_is_doc = rec["is_doc"]
+            info.append(rec)
+            continue
+        kind, _ = _strip_line_comment(s)
+        if kind is not None:
+            rec["comment"] = kind
+            rec["is_doc"] = kind == "doc"
+            info.append(rec)
+            continue
+        # Code (or blank). Blank = empty after strip.
+        rec["code"] = s != ""
+        # A code line may OPEN a raw string that spans following lines. Detected
+        # only on code (comments were handled above), so `// see r"x"` is safe.
+        m = _RAW_OPEN.search(raw)
+        if m and ('"' + "#" * len(m.group(1))) not in raw[m.end():]:
+            raw_hashes = len(m.group(1))
+        info.append(rec)
+    return info
+
+
+def violations(path):
+    lines = path.read_text(encoding="utf-8", errors="replace").splitlines()
+    info = _classify(lines)
+    n = len(info)
+    out = []
+
+    i = 0
+    while i < n:
+        rec = info[i]
+        if rec["comment"] is None:
+            i += 1
+            continue
+
+        start = i
+        if rec["is_doc"]:
+            # Doc run: contiguous doc lines. `//!` / `/*!` module docs are
+            # UNBOUNDED; any other doc run caps PROSE (fenced ``` excluded) at
+            # DOC_CAP, regardless of the documented item's visibility.
+            j = i
+            prose = 0
+            in_fence = False
+            module_doc = False
+            while j < n and info[j]["comment"] == "doc":
+                s = info[j]["s"]
+                if s.startswith("//!") or s.startswith("/*!"):
+                    module_doc = True
+                body = (
+                    s[3:] if (s.startswith("///") or s.startswith("//!")) else s
+                )
+                if _fence_toggle(body):
+                    in_fence = not in_fence
+                elif not in_fence and body.strip() != "":
+                    prose += 1
+                j += 1
+            if not module_doc and prose > DOC_CAP:
+                out.append((start + 1, prose, DOC_CAP, "doc prose"))
+            i = j
+            continue
+
+        # Internal (plain) run, with single-blank bridging (cumulative).
+        j = i
+        count = 0
+        while j < n:
+            r = info[j]
+            if r["comment"] == "plain":
+                count += 1
+                j += 1
+                continue
+            if r["comment"] == "doc":
+                break
+            if r["comment"] is None and not r["code"]:
+                # blank: bridge only a SINGLE blank, else stop
+                if j + 1 < n and info[j + 1]["comment"] == "plain":
+                    j += 1
+                    continue
+                break
+            break  # code
+        if count > INLINE_CAP:
+            out.append((start + 1, count, INLINE_CAP, "inline comment"))
+        i = j
+    return out
+
+
+def main(argv):
+    if "--selftest" in argv:
+        return _selftest()
+    root = Path(argv[1]) if len(argv) > 1 else Path.cwd()
+    files = sorted(p for d in ("src", "tests") for p in (root / d).rglob("*.rs"))
+    total = 0
+    for f in files:
+        for start, length, cap, kind in violations(f):
+            rel = f.relative_to(root)
+            print(f"{rel}:{start}: {kind} block is {length} lines (max {cap})")
+            total += 1
+    if total:
+        print(f"\ncomment-guard: {total} comment block(s) exceed their cap.")
+        print(
+            f"Inline // asides cap at {INLINE_CAP}; /// item-doc prose caps at "
+            f"{DOC_CAP} (fenced examples excluded); //! module docs are unbounded. "
+            "Trim, move the rationale into the module //!, or docs/<topic>.md "
+            "with a // pointer."
+        )
+        return 1
+    return 0
+
+
+def _selftest():
+    import tempfile
+
+    cases = [
+        # (rust source, expected number of violations)
+        # short /// doc -> ok
+        ("/// short doc\npub fn a() {}\n", 0),
+        # /// on a PRIVATE item now gets the doc cap (8), so 4 lines is fine
+        ("/// l1\n/// l2\n/// l3\n/// l4\nfn priv_a() {}\n", 0),
+        # ...but /// is NOT unlimited: 9 prose lines on a private item fails
+        ("".join(f"/// l{k}\n" for k in range(9)) + "fn priv_b() {}\n", 1),
+        # 8 prose /// on a pub item -> ok (boundary)
+        ("".join(f"/// l{k}\n" for k in range(8)) + "pub fn c() {}\n", 0),
+        # 9 prose /// on a pub item -> violation
+        ("".join(f"/// l{k}\n" for k in range(9)) + "pub fn d() {}\n", 1),
+        # /// with a long fenced example -> example excluded, ok
+        (
+            "/// summary\n/// # Examples\n/// ```\n"
+            + "".join("/// code\n" for _ in range(12))
+            + "/// ```\npub fn e() {}\n",
+            0,
+        ),
+        # pub(crate) gets the SAME doc cap as pub (no pub/private split anymore)
+        ("".join(f"/// l{k}\n" for k in range(6)) + "pub(crate) fn f() {}\n", 0),
+        # bare inline 4 lines -> violation
+        ("// a\n// b\n// c\n// d\nlet x = 1;\n", 1),
+        # blank-split dodge: 3 + blank + 3 inline -> cumulative -> violation
+        ("// a\n// b\n// c\n\n// d\n// e\n// f\nfn z() {}\n", 1),
+        # plain /* */ block, 5 lines -> inline cap -> violation
+        ("/* one\n two\n three\n four\n five */\nfn q() {}\n", 1),
+        # comment-like lines INSIDE a raw string are string data, not comments
+        (
+            'const H: &str = r##"<style>\n'
+            + "".join("/* css note */\n" for _ in range(8))
+            + '</style>"##;\nfn h() {}\n',
+            0,
+        ),
+        # //! module doc may run long -> EXEMPT (no cap)
+        ("".join(f"//! l{k}\n" for k in range(40)) + "\npub fn m() {}\n", 0),
+        # /*! block module doc may run long -> EXEMPT
+        ("/*! l0\n" + "".join(f" l{k}\n" for k in range(30)) + "*/\nfn n() {}\n", 0),
+    ]
+    ok = True
+    with tempfile.TemporaryDirectory() as d:
+        for idx, (src, want) in enumerate(cases):
+            p = Path(d) / f"case{idx}.rs"
+            p.write_text(src)
+            got = len(violations(p))
+            flag = "ok" if got == want else "FAIL"
+            if got != want:
+                ok = False
+            print(f"  selftest {idx}: want {want} got {got} [{flag}]")
+    print("selftest PASSED" if ok else "selftest FAILED")
+    return 0 if ok else 1
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))

codecov.yml

@@ -0,0 +1,18 @@
+# Coverage is informational only: it never fails CI or blocks a merge/release.
+# The `coverage` job in .github/workflows/ci.yml is non-required and no gate
+# depends on it.
+coverage:
+  status:
+    project:
+      default:
+        informational: true
+    patch:
+      default:
+        informational: true
+
+comment: false
+
+ignore:
+  - "tests"
+  - "examples"
+  - "benches"

deny.toml

@@ -0,0 +1,42 @@
+# cargo-deny — gates the RESOLVED dependency graph (issue #15).
+# Runs in CI against the committed Cargo.lock: RUSTSEC advisories, a permissive
+# licence allow-list, and source/ban hygiene. Update the lock (cargo update)
+# to clear an advisory rather than adding an `ignore` entry without cause.
+
+[advisories]
+yanked = "deny"
+# ignore = ["RUSTSEC-0000-0000"]  # only with a written justification
+
+[licenses]
+# The whole tree is permissive. r-efi's LGPL arm is satisfied by Apache-2.0
+# (its expression is "Apache-2.0 OR LGPL-2.1-or-later"), so no copyleft is
+# allowed here. Add a licence only when a real dependency introduces it.
+allow = [
+    "MIT",
+    "Apache-2.0",
+    "Apache-2.0 WITH LLVM-exception",
+    "0BSD",
+    "Unicode-3.0",
+    "Unlicense",
+    "Zlib",
+    "BSD-2-Clause",
+    "BSD-3-Clause",
+    "ISC",
+    "CDLA-Permissive-2.0",
+]
+confidence-threshold = 0.9
+
+[bans]
+multiple-versions = "warn"   # transitive dupes (digest 0.10/0.11 etc.) are noise, not a gate
+wildcards = "deny"
+# The freemkv siblings resolve as path deps under CI's path-patch layout, which
+# reads as a wildcard version req. That is internal, not a supply-chain wildcard.
+allow-wildcard-paths = true
+
+[sources]
+unknown-registry = "deny"
+unknown-git = "deny"
+# The freemkv siblings are first-party git-tag deps; allow git sources from
+# our own org only (CI resolves them as git, not the local path override).
+[sources.allow-org]
+github = ["freemkv"]

docs/aacs-content.md

@@ -0,0 +1,190 @@
+# AACS Content Decryption — Implementation Notes
+
+Rationale and background trimmed out of `src/aacs/content.rs` doc comments to
+satisfy `ci/comment-guard.py`'s per-audience prose caps. See
+[AACS Encryption](aacs.md) for the public-facing key resolution story and
+[AACS Crypto Primitives](aacs-crypto.md) for the low-level AES primitives.
+
+## `is_unit_aligned`
+
+AACS aligned units (6144 B / 3 sectors) are anchored at the start of each
+clip's encrypted region, so a read must begin a whole number of units past
+that base for `decrypt_sectors` (which anchors units at buffer offset 0) to
+align the CBC correctly. This is the single source of truth for the
+decrypt-on-read gate, the inline and highway mux read paths, and the
+key-validation sample reader — all key off this, never absolute `lba % 3`. A
+disc whose clip `start_lba` is not itself 3-aligned would otherwise mis-gate
+(reject readable units, then report "Decryption failed") on exactly the
+titles whose clips land off a 3-boundary.
+
+`saturating_sub` makes the `lba < unit_base` case well-defined — it clamps
+the offset to 0, a unit boundary — rather than the latent `wrapping_sub` trap
+where an underflow wraps to ~2^32 and, because `2^32 ≡ 1 (mod 3)`,
+mis-reports the alignment (e.g. `lba == unit_base - 1` would falsely read as
+aligned).
+
+## `aacs_unit_encrypted`
+
+The mux is the principal consumer of this signal for `BdTs` discs (via
+[`is_clean`], see below). It is readable WITHOUT a key. CRITICAL: only
+meaningful when `unit` is read at the correct clip-FILE-anchored boundary — a
+disc-absolute / mis-aligned read makes the flag byte arbitrary mid-stream
+data, which is why per-unit checks run clip-anchored, not in the whole-disc
+sweep.
+
+## `aacs_unit_needs_decrypt`
+
+Buffer-iterating sites that may run twice over the same `buf` (the post-fetch
+re-decrypt, sample collection, failure diagnosis) need an IDEMPOTENT "does
+this still need work?" test, so `aacs_unit_encrypted` (the authoritative flag,
+which decryption never rewrites) is composed with a "structure restored?"
+check that flips once decrypted: TS syncs come back for `BdTs`; valid
+`00 00 01 BA` packs come back for `MpegPs`.
+
+## HD-DVD scramble flag (`PS_SCRAMBLE_OFF` / `PS_SCRAMBLE_MASK`)
+
+BD/UHD/FMTS flag encryption uses the Copy Permission Indicator in the top 2
+bits of byte 0 (the M2TS `TP_extra_header`). HD-DVD `.evo` is Program Stream —
+byte 0 is a `00 00 01 BA` pack_start_code, NOT a CPI — so AACS reuses the
+MPEG-2 `PES_scrambling_control` field instead: pack_header (14 bytes) + PES
+start-code/`stream_id` (4) + `PES_packet_length` (2) puts the PES flags byte at
+offset 20, with `PES_scrambling_control` in bits 5-4 (`& 0x30`). Non-zero =
+encrypted. Derived from BackupHDDVD (`Header[20] & 0x30`) cross-checked
+against MPEG-2 systems (ISO/IEC 13818-1).
+
+UNVERIFIED against a real ENCRYPTED HD-DVD disc — none available to confirm
+byte-exactly. Two open questions a real disc must settle:
+1. A pack carrying an MPEG `system_header` (`00 00 01 BB`) before the PES
+   packet shifts this offset past 20.
+2. Whether offset 20 is even readable pre-decrypt. BD keeps only the first 16
+   bytes clear (the seed) and AES-CBC-encrypts 16..6144 — under that model
+   offset 20 is ciphertext. BackupHDDVD reading `Header[20]` pre-decrypt
+   implies HD-DVD instead encrypts PES *payloads* with *clear* pack/PES
+   headers (per-PES model). If so, `decrypt_unit`'s 16-byte-seed model also
+   would not fit HD-DVD and needs its own path. TS is unaffected either way.
+
+## `KEY_PROOF_PACKETS`
+
+Four `0x47` syncs are 32 bits of MPEG-TS structure, but the per-UNIT
+false-pass risk is NOT 2^-32: `is_clean_ts` accepts ANY four of the ~31
+encrypted packets in a 6144-byte aligned unit, so for a wrong key (uniform
+AES noise, `0x47` at 1/256 per packet) it is ≈ C(31,4)·256^-4 ≈ 7e-6, i.e.
+~1e-5. 1-in-4-billion is the probability for four SPECIFIC packets and
+overstates the margin by ~4000x; at `KEY_PROOF_PACKETS = 3` the per-unit rate
+is ≈ C(31,3)·256^-3 ≈ 2.6e-4, so do NOT lower it on the strength of slack
+that is not there. It is an ABSOLUTE proof floor, NOT a proportion — a unit
+the key opened but whose content is bad-encoded (many non-conforming
+packets) is proven by ANY four good packets, not rejected for the bad ones.
+
+## `is_clean_ts`
+
+The mux is its principal consumer for `BdTs` discs, reaching it through
+`is_clean`: `mux::resolve`'s multi-CPS `pick` closure selects a unit key by
+it, `probe_index_phase` reports each FMTS index's interleave parity by it,
+and `decrypt::decrypt_sectors_mapped` uses it as the forensic-range verify
+net. (The doc used to say "the mux never calls this", which invited a
+maintainer to tighten or loosen the proof rule believing only whole-disc read
+verification was affected — while it in fact changes which unit key a
+multi-CPS disc muxes with and which phase an FMTS index is muxed at.)
+
+Rule — evidence is ABSOLUTE, scaled to the packets that exist. Over the
+ENCRYPTED packets (skip packet 0: its `0x47` sits in the clear 16-byte seed,
+so it reads `0x47` for ANY key and is never evidence), let `E` = non-padding
+content packets and `synced` = those carrying `0x47`. The key opened the unit
+iff `E == 0` (nothing encrypted to prove) OR `synced >= min(E, KEY_PROOF_PACKETS)`.
+* WRONG key → ~0 synced → fails (reaching 4 by chance ≈ 1e-5/unit, and every
+  unit of a clip would have to fluke — astronomically safe).
+* RIGHT key, bad-encoded content → any 4 good packets pass; the bad ones are
+  the muxer's problem. (This is the false-negative the old 75% PROPORTION
+  caused — a mostly-bad unit the key opened was wrongly rejected.)
+* `min(E, 4)` handles the end-of-clip fragment TAIL: a unit with only E=1
+  real packet (then source-zero padding) needs just that one to sync, so a
+  sparse-but-valid tail is never false-rejected. Padding (all-zero payload)
+  is excluded throughout.
+
+## `is_clean_ps`
+
+The Program-Stream arm of `is_clean` (HD-DVD `.evo`): every 2048-byte pack
+begins with the pack_start_code `00 00 01 BA`; a 6144-byte AACS unit spans
+three packs. Pack 0's start sits in the clear 16-byte seed (present
+regardless of the key — mirrors `is_clean_ts` skipping packet 0); packs 1
+and 2 (offsets 2048 and 4096) are in the encrypted region, so a wrong key
+garbles them and this returns false (64 bits of discrimination). Validated
+against real decrypted HD-DVD `.evo` (two real retail titles): pack starts
+are exactly 2048-aligned, three per aligned unit, at offsets 0 / 2048 / 4096.
+
+UNVERIFIED-HDDVD-DECRYPT: the pack structure here is confirmed on decrypted
+rips, but that a real ENCRYPTED `.evo` decrypts to it via the same
+6144-byte aligned unit (16-byte seed + AES-CBC over 16..6144) as BD is the
+unverified assumption — we have no encrypted HD DVD. If HD-DVD decryption
+yields garbage with a known-good key, the unit granularity is the suspect.
+
+## `decrypt_unit` / `encrypt_unit`
+
+Block Key = AES-128E(Kcu, seed) ⊕ seed (`[BD]` §3.10.1 Fig 3-8: encrypt the
+clear 16-byte seed under the CPS Unit Key, XOR the seed back in — the
+trailing ⊕ seed is load-bearing); then AES-128-CBC decrypt/encrypt bytes
+16..6144 under the AACS IV. `encrypt_unit` is the exact inverse of
+`decrypt_unit`, for authoring an encrypted disc image (and for building
+genuinely-encrypted read-path fixtures); it does NOT set the encrypted flag,
+because where that flag lives is container-specific, and keeping it out
+keeps the crypto container-agnostic.
+
+Source-zero padding packets (all 192 bytes zero on disc) are restored to
+zero by `decrypt_unit`: their decrypted bytes are AES-noise from decrypting
+zeros, but the source WAS zero, so writing the true source back is faithful
+and gives the demux a tidy gap. Content packets are left EXACTLY as
+decrypted — the decrypt path never rewrites content, so an authored-bad
+packet passes through verbatim. `encrypt_unit` deliberately does NOT mirror
+this: an all-zero plaintext packet encrypts to ciphertext that is not
+all-zero, so it is not mistaken for padding on the way back and the round
+trip is still exact. Authoring that wants true source-zero padding leaves
+those packets unencrypted instead.
+
+`encrypt_unit` returns `false` — encrypting nothing — when `unit` is shorter
+than `ALIGNED_UNIT_LEN`. That case MUST be checked: the caller has already
+set the container's encrypted flag by then (the contract requires
+flag-before-crypto, since the header is the key seed), so ignoring the
+result leaves a unit marked encrypted while still carrying plaintext, which
+is the worst possible outcome for an authoring tool.
+
+## `decrypt_bus` key-schedule regression (test: `decrypt_bus_expands_the_read_data_key_once_per_unit`)
+
+MEASURED, not reasoned: `decrypt_bus` used to call `aes_cbc_decrypt` once per
+2048-byte sector, and each call built its own AES-128 key schedule, so a
+6144-byte aligned unit performed THREE key expansions under the same
+loop-invariant `read_data_key`. On a 90 GB UHD read on a stock
+(non-firmware-unlocked) drive — ~14.6 million aligned units — that is ~29
+million redundant expansions on the per-unit decrypt hot path, for a key
+that is constant for the whole disc. The counter is incremented inside
+`crypto::new_cipher`, the single construction site.
+
+## `IV0_PUBLISHED` (test fixture)
+
+`[C]` §2.1.2 fixes one default CBC IV for every AACS AES-CBC operation. Both
+IV tests used to compute their expected value from `crypto::AACS_IV` itself,
+so the constant was asserted against itself and NOTHING in the suite pinned
+its bytes: swapping `AACS_IV` for `[0u8; 16]` left both tests passing (one
+builds its ciphertext with the same value and the other cancels the change
+in a triple XOR) while every real AACS disc decrypted to noise — block 0 of
+every 6144-byte aligned unit and of every bus-encrypted sector XORed with the
+wrong IV. `IV0_PUBLISHED` is the independent witness the tests assert
+against instead.
+
+## Encrypted-flag readers (`aacs_unit_seed_encrypted`, `aacs_unit_encrypted`)
+
+`aacs_unit_seed_encrypted` is the flag reader for a PARTIAL unit — the guard
+that stops a truncated encrypted fragment from being emitted as clear
+content. It reads ONLY the two Copy Permission Indicator bits (`[BD]`
+§3.10.2, byte 0 bits 6-7); the remaining six bits are `TP_extra_header`
+arrival-timestamp bits and carry no encryption meaning. Both failure
+directions are damaging and silent: a reader that answers "encrypted" for a
+clear fragment discards good content, and one that answers "clear" for an
+encrypted fragment writes ciphertext into the output as if it were video.
+
+`aacs_unit_encrypted` is the AUTHORITATIVE gate and requires a WHOLE
+6144-byte aligned unit: on anything shorter the flag byte is not guaranteed
+to be the unit's, so it must answer `false` and leave the partial-unit case
+to `aacs_unit_seed_encrypted`. A reversed length guard would both classify
+fragments off arbitrary mid-stream bytes and, on an empty slice, index out
+of bounds.

docs/aacs-crypto.md

@@ -0,0 +1,89 @@
+# AACS Crypto Primitives — Implementation Notes
+
+Rationale and background for the internal (non-public) primitives in
+`src/aacs/crypto.rs`. See [AACS Encryption](aacs.md) for the public-facing
+key resolution and decryption story.
+
+## `aes_cbc_encrypt`
+
+Forward direction of `aes_cbc_decrypt`, and its exact inverse (`[C]` §2.1.2,
+`AES-128CBCE`). `data.len()` must be a multiple of 16; the `debug_assert!`
+documents/enforces that contract.
+
+Constructs the cipher ONCE for the whole slice. Driving this from the
+single-block `aes_ecb_encrypt` instead rebuilds the AES key schedule per
+16-byte block, which for a 6144-byte aligned unit is 383 redundant key
+expansions.
+
+## `aes_cbc_decrypt`
+
+AES-128-CBC decrypt in-place with the fixed AACS IV (`[C]` §2.1.2,
+`AES-128CBCD`). `data.len()` must be a multiple of 16; any trailing partial
+block is silently ignored. All callers pass aligned regions (6128 and 2032
+bytes), and the `debug_assert!` documents/enforces that contract.
+
+This doc was once orphaned onto `aes_cbc_encrypt` above it, when that
+function was inserted directly after it with no separating blank line:
+rustdoc rendered the crate's only forward-direction AACS primitive as
+"decrypt" and cited the spec's DECRYPT clause for it, while this function
+had no doc at all. `encrypt_unit_is_the_exact_inverse_of_decrypt_unit` in
+`content.rs` pins the directions behaviourally, so a maintainer "fixing" the
+contradiction by swapping the two bodies fails the suite instead of shipping
+a second decryptor behind an already-set encrypted flag.
+
+## `cbc_decrypt_blocks`
+
+Split out of `aes_cbc_decrypt` so a caller that decrypts several regions
+under one loop-invariant key expands the schedule once. `decrypt_bus`
+(`super::content::decrypt_bus`) is that caller: bus encryption (`[C]` §4.2 /
+the AACS 2.0 Read Data Key) covers bytes 16..2048 of EVERY 2048-byte
+sector, so a 6144-byte aligned unit is three regions under one
+`read_data_key` — three key schedules where one suffices, on the per-unit
+decrypt hot path of a whole 90 GB read.
+
+## `aes_g`
+
+AES-G(x1, x2) = AES-128D(x1, x2) XOR x2 (`[C]` §2.1.3, note: uses
+AES-128**D**). The Media Key Variant chain uses AES-G to derive both the
+variant number (`Kvn = AES-G(Kp, Nonce)`) and the Volume Unique Key
+(`Kvu = AES-G(Km, VID)`). See `super::derive::derive_vuk` for the classical
+VUK form — the math is identical, this exposes it as a neutral primitive
+for the variant chain.
+
+## `aesg3`
+
+AACS-G3 (`[C]` §3.2.2, Triple AES Generator): `left = D(k,s0)⊕s0` inc 0,
+`pk = D(k,s0+1)⊕(s0+1)` inc 1, `right = D(k,s0+2)⊕(s0+2)` inc 2. Shared
+with `super::variant` (its variant chain runs the same SD tree); a single
+definition keeps the two walks byte-identical.
+
+## Test: `S0`
+
+The AACS-G3 seed `s0`, transcribed independently from `[C]` §3.2.2 rather
+than read from `AESG3_SEED` — a test that sourced the seed from the
+production constant would assert that constant against itself and would
+still pass if it were edited.
+
+## Test: `aesg3_inverts_to_the_spec_seed_under_aes_encrypt`
+
+`aesg3` is the node function of the AACS subset-difference tree: every
+Processing Key the DK walk produces (`aesg3(node_key, 1)`) and every descent
+step (`aesg3(., 0)` / `aesg3(., 2)`) is one call. A body that returned a
+fixed block would make every device key in the crate derive the SAME
+Processing Key, and a `^` that became `|` or `&` would derive a
+wrong-but-plausible one — in both cases the MKB walk simply stops finding
+Media Keys, with no error to say why.
+
+Pinned through the spec relation rather than a re-implementation: `[C]`
+§3.2.2 defines `AES-G3` as `AES-128D(k, s) XOR s` for `s = s0 + inc` (added
+into the last seed byte), so applying the FORWARD primitive
+`aes_ecb_encrypt` — a different function from the one under test — to
+`aesg3(k, inc) XOR s` must reproduce `s` exactly.
+
+## Test: `aesg3_yields_three_distinct_subkeys_for_the_three_increments`
+
+The Triple Generator's three outputs (`[C]` §3.2.2: left = inc 0, the
+Processing Key = inc 1, right = inc 2) are the two child node keys and the
+Processing Key of ONE tree node. They must be three different keys — if
+`inc` were ignored, a descent would revisit its own parent and the walk
+would derive the same key at every level of the tree.

docs/aacs-derive.md

@@ -0,0 +1,68 @@
+# `src/aacs/derive.rs` — key derivation notes
+
+Rationale and background relocated here from doc comments in `derive.rs` to
+keep those comments within the repo's comment-length limits.
+
+## `derive_media_key_from_pk` — why the direct PK × cvalue scan
+
+A Processing Key is **terminal**: it is the key at its Subset-Difference
+node, one `AES-G` from the Media Key. So the fast path tries each PK
+*directly* against the MKB cvalue tables (no tree descent). On a large
+AACS 2.x UHD MKB (~181k cvalues) this is ~15x faster than treating a PK as
+a device-node label and walking the tree.
+
+MKB record types relevant to this path:
+
+| Type | Meaning |
+|------|---------|
+| `0x10` | Type and Version Record (has MKB version) |
+| `0x81` | Verify Media Key Record, AACS 1.0 (has `mk_dv`) |
+| `0x86` | Verify Media Key Record, AACS 2.0/2.1 (has `mk_dv`) |
+| `0x04` | Subset-Difference Index (has UVS entries) |
+| `0x05` | Media Key Data Record (cvalues, 1:1 with `0x04`) |
+| `0x07` | Explicit Subset-Difference Record (NOT cvalues) |
+
+## `recover_dk_position` — search strategy and cost
+
+This finds a device key's tree node empirically: for each MKB
+subset-difference record, it tries the device at the record's node AND at
+every ancestor v-position (the device may sit one or more levels ABOVE the
+record, descending via AES-G3 to reach it), deriving the candidate
+Processing Key DIRECTLY (one `calc_pk_from_dk` per candidate, no full
+re-walk) and checking it validates against that record's cvalue.
+
+Cost is `O(slots × tree_depth)` — linear in the MKB's subset-difference
+index, not the quartic cost of re-deriving per candidate. Slots are
+independent so the scan parallelizes (~181k slots, ~26s serial on a UHD
+MKB); `find_map_any` returns the first match and cancels the rest.
+
+## `resolve_candidate` — composed primitives and `None` conditions
+
+Composes the raw derivation primitives (`derive_media_key_from_pk`,
+`derive_media_key_and_pk_from_dk`, `derive_vuk`, `derive_unit_keys`) and
+parses `Unit_Key_RO.inf` at the version the disc's MKB declares, so a
+multi-CPS disc yields all its unit keys from the one candidate.
+
+Validate `unit_keys` against a real encrypted unit with `decrypt_unit` +
+`is_clean_ts` to prove the candidate actually opens the disc — this function
+is pure derivation, no sampling or validation.
+
+Returns `None` only when derivation itself cannot proceed: a PK its MKB
+rejects, a `Dk` the MKB can't process, a missing VID on a path that needs
+one, or an unparseable/empty `Unit_Key_RO.inf`.
+
+## Test fixtures — inverting the AACS relations
+
+There are no published AACS test vectors, but none are needed: the AACS
+relations (`[C]` §3.2.3–§3.2.5) are invertible, so a valid MKB for a CHOSEN
+key can be constructed with `aes_ecb_encrypt` and the same `aesg3` the walk
+uses as its node function. `plant_mkb` and its siblings in
+`position_recovery_tests` do exactly this — no real key material, and the
+assertions check the DERIVED Media Key, not any intermediate the code under
+test also produces.
+
+`plant_mkb`'s single-slot fixture picks `uv = 0x0400` (lowest set bit 10)
+with `u_mask_shift = 12` so a gating device node exists: `resolve_dk_node`
+flips one bit `b < 12`, and the walk's gate (`[C]` §3.2.4) needs that bit
+inside `v_mask` (`0xFFFF_FFFF << 11`) and outside `u_mask`
+(`0xFFFF_FFFF << 12`) — i.e. `b == 11`.

docs/aacs-resolve.md

@@ -0,0 +1,78 @@
+# `src/aacs/resolve.rs` — internal rationale
+
+Overflow detail relocated here by the comment-guard pass; each section is
+pointed to by a short `//` comment at the named site in `resolve.rs`.
+
+## `resolve_keys_classical`
+
+Resolve all AACS keys for a disc using the classical (single-stage Media Key
+derivation) paths. Used by both V10 and V20.
+
+Paths run in root-of-trust -> per-disc-leaf order. A match at any path
+returns immediately:
+
+1. MKB + device keys -> processing key -> media key -> VUK
+2. MKB + processing keys -> media key -> VUK
+3. KEYDB MK + matching VID -> derived VUK
+4. KEYDB disc-hash -> VUK
+5. KEYDB disc-hash -> pre-decrypted unit keys (no VUK)
+
+## `unique_verifying_mk`
+
+The MK-pool selection rule of path 2.5, split out of `resolve_keys_v1` so the
+ambiguity guard has a reachable test.
+
+`verifies` is the MKB check -- in production
+`AES-D(mk, mk_dv)[..8] == MK_VERIFY_MAGIC`. Returns a Media Key only when
+EXACTLY ONE DISTINCT candidate passes. Duplicates of the same key are one
+candidate (a pool aggregated across providers routinely repeats a key), but
+two DIFFERENT keys that both verify mean the pool cannot say which is this
+disc's Km: picking either derives a wrong VUK, and a wrong VUK decrypts to
+plausible-looking garbage rather than failing loudly. Bail and let the later
+hash/VID paths answer instead.
+
+The predicate is a parameter rather than the inlined AES check because a
+genuine two-key multi-hit cannot be synthesised: it needs one ciphertext
+that decrypts under two distinct AES-128 keys to plaintexts sharing a 64-bit
+prefix -- a 2^64 search. Injecting the verifier is the only way the
+ambiguity branch is reachable from a test at all.
+
+## Test: `mk_pool_ambiguity_bails_rather_than_picking_a_media_key`
+
+Path 2.5's ambiguity guard: when MORE THAN ONE DISTINCT pooled Media Key
+verifies against the MKB, the resolver must return no key at all rather than
+pick one. A wrong Km derives a wrong VUK, and a wrong VUK does not fail
+loudly -- it decrypts the title to garbage that muxes and plays as a corrupt
+rip.
+
+The real MKB check cannot be forced into a multi-hit: two distinct AES-128
+keys decrypting one `mk_dv` to plaintexts that share the 64-bit verify magic
+is a 2^64 search, not a fixture. So the rule is tested through
+`unique_verifying_mk`, whose verifier is a parameter -- the same function
+`resolve_keys_v1` calls, with the same pool semantics.
+
+## Test: `resolve_keys_v21_treats_the_all_zero_volume_id_as_no_vid`
+
+`resolve_keys_v21` gates paths 1 and 3 on `has_vid`, and an all-zero Volume
+ID is the crate's "the VID was never read" sentinel -- the SCSI handshake
+leaves the buffer zeroed when it does not run or fails.
+
+Both directions matter and both fail silently:
+
+- treating the zero sentinel as a real VID runs path 3 and derives
+  `Kvu = AES-G(Km, 0...0)`, a perfectly well-formed but WRONG VUK. It
+  unwraps the title keys to garbage, and nothing downstream errors -- the
+  rip just decodes to noise.
+- treating a real VID as absent skips paths 1 and 3 entirely, so a disc
+  that could have been resolved from its Media Key reports no key.
+
+Asserted through the final VUK, not through the flag.
+
+## Test: `classify_vid_present_with_material_is_no_material_not_vid`
+
+A NON-zero VID present, but resolution still fails (the providers carry
+material that doesn't resolve this disc). The VID is available, so the
+failure is NOT "VID unavailable" -- it must classify NoMaterial regardless
+of how much derivation material is present, because re-acquiring the VID is
+not the fix. This is the `has_vid == true` short-circuit, which no existing
+test covers (the gate test only uses the zero-VID sentinel).

docs/aacs-trace.md

@@ -0,0 +1,14 @@
+# AACS resolution trace shape
+
+`src/aacs/trace.rs` defines the structured trace of a resolution attempt (the
+unlock phase, then the key-resolution phase).
+
+- No user-facing English: every step's STATE is a typed enum variant.
+  Applications render these into localized text — the library never does.
+  This module only defines the shape and is wired through the
+  resolve/handshake return path far enough to compile.
+- The `who` of each step is the source's `label()` / unlocker's `name()` — a
+  stable identifier string (a NAME, like a codec id, NOT user-facing prose),
+  carried verbatim so an app renderer never has to match an enum back to a
+  name it already has. Only the OUTCOME / path enums are structured states
+  the app maps to i18n English.

docs/aacs.md

@@ -117,3 +117,100 @@ starting with `;` or `#` are comments) holding the host credentials and per-disc
 entries the library uses to resolve a disc. autorip can auto-download and
 refresh it from a configured URL. The library does not ship any AACS keys
 compiled into the binary.
+
+## `UnitKey::is_default_index` test rationale
+
+`is_default_index` is the public predicate that separates ordinary (index-0)
+content keys from FMTS forensic index keys (see `UnitKey` docs; AACS 2.1
+`IndividualSegment.tbl` tagging). A body answering `true` for everything would
+present a forensic index key as an ordinary content key -- the caller would
+decrypt the bulk of the title with a key that only opens 1/32nd of it;
+answering `false` for everything would hide every ordinary key.
+
+`is_default_index_separates_the_two_constructors` is pinned against the two
+named constructors, which are the contract: `UnitKey::new` builds the ordinary
+key, `UnitKey::forensic` builds an index key for `1..=32`.
+
+`is_default_index_agrees_with_the_forensic_index_resolver` checks the
+predicate agrees with the one consumer of `index_number` in the crate:
+`crate::aacs::index_select::resolve_disc_index` resolves the disc's forensic
+index from exactly the keys that are NOT default. If the two disagree, a disc
+resolves an index whose key the rest of the pipeline treats as ordinary (or
+vice versa).
+
+## `src/aacs/mod.rs` module notes
+
+### KEYDB.cfg line format
+
+```
+| DK | DEVICE_KEY 0x... | DEVICE_NODE 0x... | KEY_UV 0x... | KEY_U_MASK_SHIFT 0x...
+| PK | 0x...
+| HC | HOST_PRIV_KEY 0x... | HOST_CERT 0x...
+| HC2 | HOST_PRIV_KEY 0x... | HOST_CERT 0x...
+0x<disc_hash> = <title> | D | <date> | M | 0x<media_key> | I | 0x<disc_id> | V | 0x<vuk> | U | <unit_keys>
+```
+
+### Spec provenance tags
+
+The crypto in `src/aacs/` carries `[TAG] §x.y` citations back to the published
+AACS specification (Final Rev 0.953), so each primitive links to the section it
+implements:
+
+- `[C]` -- AACS Introduction and Common Cryptographic Elements Book (primitives,
+  MKB/key-management).
+- `[PR]` -- AACS Pre-recorded Video Book (Volume/Title Key layer).
+- `[BD]` -- AACS Blu-ray Disc Pre-recorded Book (CPS Unit Key, Aligned Unit,
+  Block Key).
+- `[RE]` -- reverse-engineered from real discs, cited only where the public
+  spec is silent (the `0x86` verify record and the Category-C MKB type values).
+
+### AACS key-input path discovery (`AacsRole`, `role_paths`, `find_hddvd_aacs_dir`)
+
+BD and UHD keep their key material under a fixed `/AACS/...` tree, so those
+paths are constants. HD DVD keeps the equivalents in a reserved root directory
+whose NAME is authoring-house-specific -- observed `ANY!` (Dukes of Hazzard)
+and `AAC!` (Freedom / Memory-Tech), each with a `<name>!_BAK` mirror -- and
+whose title-key file is NOT always `VTKF000.AACS` (Freedom ships
+`VTKF090.AACS` + `VTKF100.AACS`). So the HD DVD files are DISCOVERED from the
+parsed UDF tree (`find_hddvd_aacs_dir` + `role_paths`), never hardcoded.
+
+Each key role (`AacsRole`) resolves to an ordered candidate list -- the BD/UHD
+constants first, then whatever the HD DVD directory actually holds -- which
+every reader walks with `read_first`, first-that-reads. No reader ever
+branches on disc type: a BD/UHD disc has the `/AACS/` files so those win; an
+HD DVD has none of them, so it falls through to the discovered entries.
+Centralised so `resolve_vid_only`, `read_aacs_inputs`, `read_mkb_content`, and
+`read_aacs_version` can never silently diverge the disc_hash / MKB / VID that
+another reader feeds a key service.
+
+`find_hddvd_aacs_dir` identifies the HD DVD AACS directory structurally, NOT by
+a hardcoded name: the root child directory whose name ends in `!` (so the
+`<name>!_BAK` backup mirror, which also ends in a non-`!` char, is not
+mistaken for it) and which contains `MKBROM.AACS`. Observed real names:
+`ANY!` (Dukes of Hazzard), `AAC!` (Freedom). A BD/UHD disc has no such
+directory -> `None`.
+
+`role_paths` builds the ordered candidate list: fixed BD/UHD paths first, then
+the discovered HD DVD files. For `AacsRole::UnitKey` every `VTKF*.AACS` in the
+directory is appended in sorted name order -- a disc may carry more than one
+variant (Freedom: `VTKF090` + `VTKF100`), not just `VTKF000`.
+
+`read_first` walks an AACS role's candidate paths and returns the first that
+reads; `read` performs the actual per-path read (full file or bounded prefix),
+so callers share the same first-present walk regardless of read style. Returns
+`Error::AacsNoKeys` if no candidate is present. Generic over the path element
+(`&str` or owned `String`) so it accepts the `Vec<String>` that `role_paths`
+builds from the discovered HD DVD directory.
+
+### Test: `a_bang_suffixed_directory_without_mkbrom_is_not_the_aacs_directory`
+
+The `!`-suffix and the `MKBROM.AACS` presence test are BOTH required -- the
+discovery is a conjunction, not a disjunction. The existing fixtures only ever
+present a directory that satisfies both (`AAC!` with `MKBROM.AACS`) alongside
+one that satisfies neither (`AAC!_BAK` -- which contains `MKBROM.AACS` but is
+ALSO reached only after the real dir), so either half of the conjunction could
+be dropped and the same directory would still be found. This test's fixture
+has a directory that satisfies the name half and NOT the contents half: it
+must not be picked. If it were, the HD DVD path would resolve `MKBROM.AACS`,
+`CONTENT_CERT.AACS` and the title-key file under a directory that holds none
+of them -- the disc reports "no AACS key files" and never rips.

docs/ac3.md

@@ -0,0 +1,220 @@
+# AC3 / E-AC3 parser notes (`src/mux/codec/ac3.rs`)
+
+## Why a frame set is one sample, never split into separate tracks
+
+A legacy AC-3 syncframe is a complete access unit on its own, but an E-AC-3
+access unit (ETSI TS 102 366 / ATSC A/52 Annex E) is a whole FRAME SET: the
+mandatory independent substream (`substreamid` 0) plus every DEPENDENT
+substream frame that follows it, plus any ADDITIONAL independent substreams
+(`substreamid` 1..7) and their own dependents. A decoder needs the whole set
+to reconstruct the programme (a 5.1 independent substream plus a dependent
+substream carrying the extra channels of a 7.1 programme, and the AC-3-core +
+E-AC-3-dependent arrangement used for backwards-compatible Dolby Digital
+Plus), and every substream of the frame set covers the SAME time period.
+
+WHY the whole frame set is ONE sample, rather than splitting an additional
+independent substream (an associated / commentary service) into a track of
+its own: Annex E orders the substreams of a frame set inside a single
+elementary stream, all covering one time period, and a decoder handed a frame
+set renders the programme it is asked for from it — that is exactly what the
+container's E-AC-3 sample and its `dec3`/`num_ind_sub` description denote.
+Splitting would mean rewriting the bitstream (re-numbering `substreamid` so
+the extracted service becomes substream 0, and rebuilding its frame sets),
+because a substream numbered 1..7 with no substream 0 is not a conforming
+stream. That is a transcode, not a remux; this parser is lossless, so the
+frame set stays whole and player-side programme selection decides what is
+heard.
+
+## `SAMPLE_RATES` / fscod2
+
+Sample rates indexed by fscod (0=48kHz, 1=44.1kHz, 2=32kHz). fscod=3 is
+reserved in AC-3; in E-AC-3 it signals "fscod2" (reduced rates: 24/22.05/16
+kHz, selected by byte-4 bits `[5:4]`). `frame_sample_rate` decodes fscod2 in
+the E-AC-3 case; the table's index-3 entry (48 kHz) is only the fallback when
+the header is too short to read fscod2.
+
+## `MAX_AC3_BUF` derivation
+
+An AC-3/E-AC-3 syncframe is at most 8192 bytes (the `frame_size > 8192`
+reject) and an access unit is a whole frame set: up to 8 independent
+substreams, each with up to 8 dependent substreams (ETSI TS 102 366 Annex E)
+— 72 syncframes worst case. A cap of one straddling frame set plus slack
+therefore has to exceed 72 × 8192 = 576 KiB. If the buffer grows past the cap
+without yielding a frame (pathological / never-syncing input) it is dropped
+and resync begins, rather than accumulating one PES worth of data per call
+for the whole title.
+
+## `scan_access_units`
+
+Per ETSI TS 102 366 (ATSC A/52) Annex E an access unit is one FRAME SET: the
+mandatory independent substream (`substreamid` 0) plus every DEPENDENT
+substream that follows it, plus any ADDITIONAL independent substreams
+(`substreamid` 1..7 — associated/commentary services) with their own
+dependents. The access unit therefore closes only when the next
+`substreamid`-0 independent substream (or, with `at_eos`, the end of the
+stream) is seen, and it carries THAT substream's PTS and duration: every
+other substream of the frame set describes the SAME time period and adds no
+duration of its own.
+
+`base_pts_ns` times the access unit that begins at `data[0]` — i.e. the
+running cadence carried over from the previous call. `anchor` re-anchors the
+running PTS to this PES's own timestamp at the first access unit that STARTS
+in the newly-appended bytes: a PES timestamp applies to the first access unit
+beginning in that PES, never to one that began in an earlier PES and is only
+being completed (or was held) here.
+
+Returns the emitted access units, the offset in `data` from which bytes must
+be carried over to the next call, and the PTS to stamp on the access unit
+that begins that carry-over.
+
+## `substream_role`
+
+Byte 2 of an E-AC-3 syncframe is `strmtyp(2) | substreamid(3) | frmsiz[10:8]`
+(ETSI TS 102 366 Annex E BSI). `strmtyp` 0 and 2 are independent substreams
+(type 2 being an independent substream that is not the first of the bit
+stream); `strmtyp` 1 is the dependent substream.
+
+Annex E defines a FRAME SET as independent substream 0 — mandatory, always
+first — with its dependent substreams, followed by the OPTIONAL additional
+independent substreams 1..7, each with their own dependents; all of them
+carry the same time period. So the access-unit boundary is an independent
+substream with `substreamid` == 0, and NOT merely "an independent substream":
+an additional independent substream (an associated or commentary service)
+sits INSIDE the frame set already open. Keying the boundary on `strmtyp`
+alone made every such substream close the access unit and advance the
+running PTS a second time over the same ~32 ms, doubling the timeline (about
+a second of A/V drift per second of audio).
+
+`strmtyp` 3 is reserved: its BSI layout is not defined, so its `substreamid`
+bits cannot be trusted and it is treated as starting a fresh access unit — an
+unknown frame is never merged into an unrelated programme, and never
+discarded as an orphan either.
+
+Legacy AC-3 (`bsid < 11`) has no substream structure — byte 2 there is the
+crc1 field, never `strmtyp` — so it always starts an access unit.
+
+A frame set MAY carry a substream as several consecutive syncframes of fewer
+than six blocks each (Annex E allows numblkscod < 3). Those extra syncframes
+are `substreamid` 0 too, so each starts its own access unit here rather than
+merging into one frame set. That is deliberate: each carries its OWN
+numblkscod-derived duration (see `frame_duration_ns`), so the timeline total
+stays exact, and the substreams are still delivered in bitstream order.
+
+## `frame_crc_ok`
+
+Per ETSI TS 102 366 (ATSC A/52) the frame carries a CRC-16/ANSI (poly 0x8005,
+init 0, non-reflected) over the bytes after the 2-byte syncword — i.e.
+`crc16_ansi(&buf[2..]) == 0` covers `frame_size - 2` bytes; the trailing crc
+word makes a clean frame's residue zero. A nonzero residue is a
+~1-in-65536-certain sign of payload corruption, so the frame is dropped
+(silence gap) rather than shipped as a glitch.
+
+## `acmod_channels` bit layout
+
+This is the AUTHORITATIVE channel count for the track header: the DVD IFO
+`audio_attr_t.channels` nibble is a well-known unreliable/stale field, so the
+muxer prefers this over the IFO-claimed count (the bitstream acmod is
+authoritative; the IFO audio nibble is not trusted). LFE adds one channel
+(e.g. acmod=7 + lfeon → 6 = 5.1).
+
+Bit layout from the syncword (A/52 §5.3.2 BSI):
+
+```text
+  byte 5: bsid(5) | bsmod(3)
+  byte 6: acmod(3) | [cmixlev(2) if acmod has a centre and acmod!=1]
+                   | [surmixlev(2) if acmod has surround]
+                   | [dsurmod(2) if acmod==2] | lfeon(1) | ...
+```
+
+`acmod` therefore always occupies byte-6 bits 7-5; `lfeon` follows a variable
+number of optional 2-bit fields, so the decoder tracks the bit cursor.
+
+## `ACMOD_CHANNELS` table
+
+Base channel count per AC-3 `acmod` (A/52 Table 5.8), BEFORE the LFE. Index is
+the 3-bit acmod value; add 1 when `lfeon` is set.
+
+```text
+  0 = 1+1 (Ch1, Ch2)  -> 2     4 = 2/1 (L,R,S)        -> 3
+  1 = 1/0 (C, mono)   -> 1     5 = 3/1 (L,C,R,S)      -> 4
+  2 = 2/0 (L, R)      -> 2     6 = 2/2 (L,R,SL,SR)    -> 4
+  3 = 3/0 (L,C,R)     -> 3     7 = 3/2 (L,C,R,SL,SR)  -> 5
+```
+
+## Test helpers and coverage notes
+
+### `finalize_ac3_crc`
+
+Relies on the CRC-16/ANSI residue property: appending `crc16([2..n-2])`
+(big-endian) zeroes the register over `[2..n]`.
+
+### `the_working_buffer_is_reused_across_packets_not_reallocated`
+
+`parse` runs once per PES packet — of the order of 10^5 times on a feature's
+audio track — and used to build a fresh `Vec` every call. The copy itself
+cannot go without restructuring the borrow relationship, but the allocation
+can: the buffer is taken out of `self`, filled, and put back with its
+capacity intact. Asserting on capacity is deliberately white-box, because
+that is exactly what regresses if someone reverts to `to_vec()` — the
+behaviour would be identical and no other test would notice.
+
+### `make_eac3_frame` byte layout
+
+ETSI TS 102 366 Annex E: byte 2 is strmtyp(2) | substreamid(3) | frmsiz[10:8],
+byte 3 is frmsiz[7:0], and the frame is `(frmsiz + 1) * 2` bytes. byte 4 =
+fscod 0 (48 kHz), numblkscod 3 (6 blocks → 1536 samples → 32 ms), acmod 7 +
+lfeon (5.1); byte 5 = bsid 16 so the E-AC-3 paths are taken.
+
+### `a_held_access_unit_is_not_rescanned_from_its_first_frame_every_packet`
+
+An access unit closes only at the next `substreamid`-0 independent substream,
+so one that keeps gaining dependent substreams stays OPEN across PES
+boundaries and its bytes stay in the carry-over. The carry-over must not be
+re-scanned — and re-CRCed — from the access unit's first byte on every
+packet: the buffer only stops growing at `MAX_AC3_BUF` (1 MiB), and a PES on
+a DVD is about 2 KiB, so re-deriving the held access unit costs work
+quadratic in the packets fed.
+
+Measured directly, because a work bound has no frame-level shadow:
+`frames_scanned` counts the syncframes the scanner sizes and CRC-gates.
+Re-scanning from byte 0 examines 1 + 2 + ... + (N+1) frames.
+
+Mutation: pass `None` for `held` in `parse` (or drop the `if let Some(h) =
+held` resume) — the count returns to the quadratic figure.
+
+### `a_discontinuity_drops_the_held_access_unit_with_its_bytes`
+
+`parse` clears `self.acc` on a discontinuity because the buffered bytes are a
+truncated frame. The held access unit is described by OFFSETS into exactly
+those bytes, so it has to go with them. Without `self.held = None`, the next
+packet resumes a HeldAu whose `start`/`end` were computed against the
+pre-gap buffer but are applied to the unrelated post-gap bytes — splicing
+audio across the gap at best, and indexing past the end of the new, shorter
+buffer at worst.
+
+The two existing discontinuity tests use plain AC-3 (bsid < 11), which never
+holds an access unit open, so neither of them reaches this reset.
+
+### `a_held_access_unit_is_dropped_when_the_track_poisons_before_it_resumes`
+
+Mutation this catches: deleting (or inverting) the resume-path re-check `if
+drop_reason.is_none() && self.tally.is_poisoned()` at the top of
+`scan_access_units`. The verdict on a held access unit is frozen at the
+moment it was OPENED, and `ac3_drop_reason` reads the tally BEFORE the
+previous access unit is closed — so the very drop that crosses the poison
+threshold lands after the next unit's verdict was already taken as `None`.
+Without the re-check that unit is emitted as an ordinary frame after the
+track has been judged too damaged to mux: corrupt audio passed through as
+success, and worse, it is the ONE frame that escapes a whole-track fallback
+whose entire point is that nothing after the verdict ships.
+
+Neither existing held-AU test reaches this: both keep a pristine tally.
+
+The fixture drives the exact interleaving above. `DropTally` poisons once
+`verified_dropped * 2 > kept + dropped` past the 200-AU gate, so one PES
+carries 200 CRC-failing `substreamid`-0 syncframes followed by a clean one.
+Closing corrupt unit #200 (which happens only when the clean frame is
+reached) latches the poison — after that clean frame's own verdict was
+computed. Being an E-AC-3 unit that can still gain substreams, it is then
+HELD across the boundary with `drop_reason: None`, which is precisely the
+state the re-check exists for.

docs/adts.md

@@ -0,0 +1,37 @@
+# ADTS decodability gate
+
+## Module rationale (`src/mux/codec/adts.rs`)
+
+Per the ADTS framing defined in ISO/IEC 13818-7 / ISO/IEC 14496-3, a header
+is structurally invalid in exactly three ways this gate treats as hard
+rejects: syncword != 0xFFF, a reserved `sampling_frequency_index` (the sample
+rate table has 13 valid entries, so index >= 13 is reserved), and
+`aac_frame_length < 7` (shorter than the fixed+variable header itself). The
+optional 16-bit ADTS CRC is not verified here — it is simply skipped. So the
+gate enforces those three rejects: a packet that begins with the ADTS sync
+but is otherwise malformed is dropped; a packet with no ADTS sync is raw AAC
+(e.g. from an MP4 container, which carries no ADTS header) or a continuation
+and passes through unchanged — never false-dropped. Raw AAC has no per-frame
+integrity data, so like LPCM it cannot be gated.
+
+## Test: `a_crc_present_header_shorter_than_its_own_crc_is_invalid`
+
+A header that CLAIMS a CRC (protection_absent = 0) but declares a frame
+length too short to contain one.
+
+`aac_frame_length` counts the header and the CRC, not just the payload,
+so with a CRC present the smallest structurally possible frame is 9
+bytes: the 7-byte fixed+variable header plus the 16-bit crc_check.
+The gate compared against a flat 7 and never read protection_absent at
+all, so a frame whose own header says it is impossible was classified
+Valid and forwarded to the muxer.
+
+## Test: `dropped_frames_are_counted_but_their_duration_is_not_invented`
+
+A dropped ADTS frame is dropped BECAUSE its header failed validation, so
+the very fields a duration would come from (sampling_frequency_index, and
+the 1024-samples-per-AAC-frame constant applied to it) are the ones known
+to be untrustworthy. This gate therefore reports the drop's duration as
+zero rather than deriving a number from a header it has just rejected —
+the honest answer, and the one the count alongside it must be read with.
+A nonzero constant here would report silence that was never measured.

docs/au-assembly.md

@@ -0,0 +1,217 @@
+# `src/mux/au_assembly.rs` — access-unit assembly
+
+## Why this exists
+
+The contract a codec parser converts is `PES → access units (Frames)`. A
+*transport* stream hands the parser one AU per PES for free (BD aligns one
+access unit per PES; the TS demuxer reassembles to the
+`payload_unit_start_indicator`). A *program* stream does not — the PS muxer
+chops the elementary stream into fixed-size PES fragments with no AU
+alignment, and only the first fragment of an AU carries a PTS. So a parser
+that assumes one-AU-per-PES (h264/hevc/vc1, written against TS) mis-frames a
+program stream, while `mpeg2` — the DVD/PS codec — must reassemble across PES.
+
+`AuAssembler` is that reassembly, factored out so EVERY program-stream video
+parser shares one implementation instead of hand-rolling the buffer. The
+h264/hevc/vc1 parsers (`Mode::StartCode` / `Mode::Vc1`) and the MPEG-2 parser
+(`Mode::Mpeg2`, via `AuAssembler::mpeg2`) all drive it. It buffers PES-fragment
+bytes and emits one AU per codec AU boundary, carrying the AU-start
+timing/source forward. Since the boundary is a codec start code, it lives with
+the codec parser (which picks the marker); only the generic buffering +
+timing-carry is shared here.
+
+This is *inside* the parser, not a pipeline stage: the pipeline stays
+`Demuxer → PES → Parser → Frames`, and the demuxer stays codec-agnostic. Every
+stream a parser sees runs through one of these — self-framing codecs (MPEG-2,
+audio) use `Mode::Passthrough` so the parser code path is uniform.
+
+## `MAX_AU_BUFFER`
+
+Safety cap on a single in-progress access unit. A real coded picture is far
+below this; a stream that never yields a second AU boundary is force-flushed
+at the cap rather than buffering without bound on hostile/corrupt input.
+
+## `MAX_MARKS`
+
+Cap on buffered timing/discontinuity marks. A real access unit spans a few
+hundred PES fragments at most; this bounds the mark deques so a run of
+zero-length (or start-code-free) timed fragments — which grow no buffer bytes
+and so never trip the `MAX_AU_BUFFER` mark-prune — cannot accumulate marks
+without bound on hostile/corrupt disc input.
+
+## `AuAssembler::for_codec`
+
+Video codecs whose parsers assume AU-complete PES (H.264 / HEVC / VC-1) get a
+`Mode::StartCode` assembler; MPEG-2 (self-reassembles) and audio/subtitle
+codecs (self-framing) get `Mode::Passthrough` so callers can run every stream
+through this uniformly.
+
+## `AuAssembler::mpeg2`
+
+The MPEG-2 parser owns one of these directly (rather than hand-rolling the
+buffer): the demux layer runs MPEG-2 through `Mode::Passthrough` and hands
+each fragment to the parser, which feeds them here to be reframed on picture
+boundaries.
+
+## `AuAssembler::push`/`push_owned`
+
+For a self-framing (`Passthrough`) stream the payload is MOVED straight into
+the emitted unit with no copy — the common DVD/HD-DVD case (MPEG-2 video, all
+audio). A buffering mode copies into `buf` exactly as `push`.
+
+## `take_front`
+
+Detaches `buf[..end]` as the emitted AU's own `Vec` and leaves `buf` holding
+the tail.
+
+The AU's bytes are HANDED OVER — `buf`'s allocation becomes the returned `Vec`
+and a fresh buffer (pre-sized to the same capacity, so the next AU accumulates
+without re-growing) takes its place holding only the short tail.
+`buf[..end].to_vec()` + `drain(..end)` instead copied every AU out in full: on
+a UHD HEVC title that is a whole-frame memcpy (hundreds of KB) per coded
+picture, ~200k times, for bytes that are about to be discarded from `buf`
+anyway.
+
+The allocation COUNT is unchanged (one per AU either way — the frame `Vec`
+before, the replacement buffer now), so the only difference is the copy that
+no longer happens. Nothing depends on `buf` keeping its identity: the only
+state tied to `buf[0]`'s position is `base`/`scan_pos`/`opener_pos`, which the
+caller updates immediately after.
+
+Falls back to a copy when the buffer's capacity is far larger than the AU (a
+small AU after a multi-MB one): handing over would otherwise attach an
+oversized idle allocation to a small frame for as long as the frame queues
+downstream, trading a copy for resident memory.
+
+That fallback must not become permanent. `buf`'s capacity used to be a one-way
+high-water mark — the replacement buffer was created with `cap.max(tail_len)`,
+and the copy path's `drain` also preserves `cap` — so once ONE large AU had
+been assembled, every later smaller AU satisfied `cap > 2*end` and took the
+copy path forever. On a UHD HEVC title the first IDR grows `buf` to ~4-8 MB,
+after which each ~200-400 KB P/B AU paid a whole-AU allocation plus a
+whole-AU memcpy plus a tail memmove for ~99% of the ~200,000 coded pictures —
+tens of GB of exactly the memcpy this handover exists to remove. So the copy
+path now also RELEASES the high-water capacity, which re-arms the handover
+for the next AU: one copy after a size step down, not one per frame forever.
+
+## `drop_marks_before`
+
+This is the STREAM-START case: bytes ahead of the first AU boundary are the
+tail of an access unit that began before we had sync, and there is no prior
+AU for them to be discontinuous *from*. Carrying a mark forward here would arm
+the resync gate at the head of every title and drop its first GOP.
+
+## `discard_gap_before`
+
+This is the BACKSTOP case: `MAX_AU_BUFFER` bytes accumulated with no AU start
+code in them, so the run is unusable and gets thrown away. Unlike the
+stream-start trim above, there IS a prior AU here, and whatever follows
+definitively does not continue it — a decoder handed the next picture would
+resolve its references against frames separated from it by megabytes of
+discarded data.
+
+So the discard is itself a discontinuity, whether or not the source signalled
+one. It is recorded as a sticky flag rather than an offset mark because a
+mark placed at the new base would be retired moments later by the pre-sync
+trim that follows resync — the gap has to outlive the bytes that caused it.
+It arms the resync gate, which drops to the next keyframe instead of emitting
+a picture with dangling references.
+
+Timing marks before `off` are still retired — they describe bytes that no
+longer exist, and the AU that eventually emits takes its PTS from the
+fragment that actually opened it.
+
+## Tests
+
+### `a_backstop_discard_marks_the_next_au_discontinuous`
+
+The 8 MiB backstop throws away a start-code-free run as unusable. The AU that
+eventually emits after that discard MUST be marked discontinuous, whether or
+not the source ever signalled a discontinuity: megabytes of the stream are
+simply gone, so the next picture cannot resolve its references against the
+last one that was emitted.
+
+`discontinuity` is what arms the resync gate downstream (`resync.rs`, driven
+from `mux/disc.rs`), which drops to the next keyframe rather than emitting a
+picture with dangling references. If the flag is retired with the discarded
+bytes, the gate never arms and the broken picture goes out — a silent
+corruption, which is the one class of loss this crate refuses to have.
+
+### `a_stream_start_trim_does_not_mark_the_first_au_discontinuous`
+
+The opposite case, and the reason the two call sites are separate. Bytes
+ahead of the FIRST access-unit delimiter are the tail of an AU that began
+before we had sync. There is no prior AU for them to be discontinuous from, so
+retiring the marks there is right — and necessary: marking the first AU of
+every title discontinuous would arm the resync gate at the head of each one
+and drop its opening GOP.
+
+### `a_source_signalled_discontinuity_reaches_the_au_it_opens`
+
+A source-signalled discontinuity reaches the AU it opens. This is the
+`disc_marks` path — the ORIGINAL mechanism, distinct from the sticky
+`pending_gap` the backstop sets. Nothing else pins it: the two tests above
+drive `pending_gap`, and a mark placed on a fragment that is later discarded
+is retired by design.
+
+Deliberately NOT combined with the backstop. A previous version of this test
+signalled the discontinuity on the first over-cap push and asserted the flag
+on the AU after the discard — but that first run still has the next AU's
+delimiter at `buf[0]`, so it force-flushes as an over-long AU, and THAT AU
+consumes the mark. The assertion was then satisfied entirely by
+`pending_gap`, making the test a duplicate of the one above it under a name
+promising something else. The two mechanisms cannot be isolated in one
+fixture, so they get one test each.
+
+### `drained_au_takes_over_the_buffer_allocation_without_copying`
+
+MEASURED: a drained AU must be HANDED the accumulation buffer's allocation,
+not copied out of it. The emitted `Vec`'s data pointer is the buffer's own
+pointer — which is only true if no full-frame copy happened.
+(`buf[..end].to_vec()` allocates fresh, so the pointers differ.) One
+whole-AU memcpy per coded picture is ~200k memcpys of a few hundred KB each
+on a UHD feature.
+
+### `handover_survives_a_large_au_instead_of_copying_every_later_one`
+
+MEASURED: `take_front`'s copy fallback must not become permanent.
+
+`buf`'s capacity used to be a one-way high-water mark, and the copy path's
+`drain` preserves it, so after ONE large AU every later smaller AU satisfied
+`cap > 2*end` and copied forever. On a UHD HEVC title the first IDR grows
+`buf` to multiple MB, after which ~99% of the ~200,000 coded pictures each
+paid a whole-AU allocation + whole-AU memcpy + tail memmove — tens of GB of
+exactly the copy the handover exists to remove. Counted at the copy path
+itself: one copy is expected right after the size step down; a per-frame
+copy is the bug.
+
+### `discarded_pre_sync_marks_do_not_time_the_first_access_unit`
+
+After the pre-sync bytes are discarded, the emitted AU must take the timing
+of the fragment that ACTUALLY opened it. `drop_marks_before` is what retires
+the discarded fragment's marks; a no-op there stamps the first real access
+unit with the PTS and source of bytes that were thrown away — a whole-title
+A/V sync offset, since every later frame is timed relative to it.
+
+### AU-opener detection: the per-mode start-code rule
+
+`au_opener_from` duplicates a rule each codec parser also encodes; the tests
+below pin it to the normative byte values so a drift between copies shows up.
+
+### `au_opener_from_locates_the_real_start_code_per_codec`
+
+The opener offset must be the position of the real start code, never a fixed
+0. A constant `Some(0)` makes every pre-sync run of junk bytes look like the
+head of an access unit, so the first AU of every stream that does not begin
+exactly on a start code is emitted with junk glued to its front.
+
+### `for_codec_routes_each_video_codec_to_its_reassembly_mode`
+
+`for_codec` is the dispatch that decides whether a stream is REASSEMBLED
+across PES fragments or passed straight through. Getting it wrong is silent:
+an H.264/HEVC/VC-1 stream routed to `Passthrough` on a program source emits
+one "frame" per PES fragment — a few hundred bytes of a coded picture, framed
+as a whole access unit — and the output plays as corruption, not as an error.
+
+Each mode is identified BEHAVIOURALLY (feed a two-AU stream in two halves and
+see whether it reassembles), so the case cannot pass by matching a constant.

docs/bdmt.md

@@ -0,0 +1,42 @@
+# BDMV disc-library metadata (`bdmt.rs`)
+
+Every commercial Blu-ray carries a disc-library metadata directory with one
+XML file per shipped language. The schema is the Blu-ray "disc library
+metadata" namespace (`urn:BDA:bdmv;disclibmeta`), conventionally prefixed
+`di:`. Fields commonly present:
+
+- `<di:title>` or `<di:name>` — the title string. Vendor practice varies
+  (Paramount discs tend to use `<di:name>`).
+- `<di:description>` — optional synopsis (often absent on retail discs;
+  common on box sets and special editions).
+- `<di:discNumber>` / `<di:numSets>` (or `<di:numberOfSets>`) — set position
+  for multi-disc releases.
+
+This module is intentionally separate from the BD-J `StreamLabel` parsers
+under `labels/*.rs`. The XML here is disc-level (title, description, set
+position), not per-stream.
+
+Real-world XML is irregular: missing description elements, multiple title
+elements (first one wins), and occasional malformed content. Extraction is
+best-effort — a malformed file is treated as "no metadata" (returns `None`
+from the helper), and the caller can still get metadata from
+sibling-language XML files.
+
+## `MAX_BDMT_BYTES`
+
+The size comes from attacker-controlled UDF metadata; real files are a few
+KB, so 1 MiB is generous while preventing a crafted huge-size entry from
+triggering an oversized allocation in `read_file`.
+
+## `parse_bdmt_xml`
+
+Title-element preference: `<di:name>` → `<di:title>` →
+`<di:tableOfContents>/<di:titleName>` (first match wins, per the
+authoring-tool conventions documented above).
+
+## `looks_like_xml`
+
+Rejects candidate description strings that are themselves XML fragments —
+observed on a captured disc, where `<di:description>` contained
+`<di:thumbnail href="…"/>` child elements and no actual prose. Surfacing
+that raw to the JSON output is worse than dropping the field entirely.

docs/bdnav.md

@@ -0,0 +1,21 @@
+# bdnav — HDMV navigation resolver
+
+Notes relocated from `src/bdnav/mod.rs` doc comments (kept out of the source
+to respect the comment-guard's prose caps).
+
+## No per-disc special-casing
+
+There is no per-disc special-casing: one correctly-booted VM resolves
+densely-branched dispatchers as well as simple ones. The honest boundary is
+BD-J (the feature is chosen by a Java Xlet, not by the HDMV VM); there — and
+on any malformed data or non-convergence — the resolver ABSTAINS (`None`)
+and selection falls back to the structural/heuristic order.
+
+## `resolve_feature`
+
+Resolves the playlist id the disc's First-Play navigation plays as the
+feature, restricted to ids the caller marks as feature candidates
+(`is_feature_candidate` — typically video-bearing, non-trivial titles, so a
+short logo/pre-roll `PlayPlayList` is skipped). Returns `None` for BD-J
+discs, missing/malformed nav data, or when navigation does not converge on
+a candidate.

docs/bluray.md

@@ -0,0 +1,239 @@
+# src/disc/bluray.rs — extended notes
+
+Overflow prose for comments that were trimmed to the internal 3-line cap in
+`src/disc/bluray.rs`. Each section is pointed to by a `// See docs/bluray.md
+— <topic>` comment at the corresponding site.
+
+## CLIP_STREAM_EXTS
+
+Stream-file extensions probed for a BD-family playlist clip, in priority
+order. A clip is normally `.m2ts`; AACS 2.1 (FMTS) discs name the main
+feature `.fmts` (an M2TS transport stream plus forensic variant segments)
+and 3D discs use `.ssif`. `.m2ts` is tried first, so a normal clip is
+unaffected — the fallback only runs when `.m2ts` is absent (exactly when
+`file_extents` errors).
+
+Scope: these are all variants that live in `BDMV/STREAM/` and are reached
+through an MPLS playlist. HD-DVD's `.evo` does NOT belong here — HD-DVD is
+a different tree (`HVDVD_TS/`) with `.XPL` playlists and needs its own
+enumerator (a peer to `parse_playlist`), not another extension in this
+list.
+
+## scan_bluray_titles
+
+Cancellation: `halt` is polled between playlists and once more after the
+loop, and a read that fails with `Error::Halted` — how a live drive
+reports a Stop, since `Drive::checked_exec` fails every command once its
+flag is set and `Drive::read` preserves the variant — is propagated rather
+than swallowed. `Halted` is the only error this returns from the
+enumeration itself; an unreadable or unparseable playlist keeps its
+best-effort skip.
+
+It has to be an error and not a short title list, for the same reason
+spelled out on `Disc::scan_hddvd_titles`: a cancelled enumeration that
+returned `Ok` would be indistinguishable from a disc that genuinely holds
+fewer titles, and the caller would cache and act on it. Before this, a Stop
+pressed mid-scan failed every remaining `.mpls` read in turn, each one
+silently skipped, and the scan returned `Ok(truncated)` at rc=0.
+
+## parse_playlist
+
+Sums PlayItem durations; returns `Ok(None)` if the playlist is under 30
+seconds (skips menu / clip-info stub playlists), fails to parse, or names a
+clip that cannot be resolved. Physical sector extents are pulled from the
+UDF allocation descriptors of each referenced `.m2ts` (deduplicated by
+clip_id).
+
+`Ok(None)` keeps its two benign meanings (unparseable MPLS, sub-30s
+playlist) plus the deliberate "drop this title" outcomes below. `Err` means
+the scan is over: today that is only `Error::Halted`, the operator's Stop,
+which must not be reported as a disc that simply holds fewer titles.
+
+## Test: parse_playlist_keeps_exactly_30_seconds
+
+At exactly 30s the playlist is kept (`< 30.0` is strict). The fixture is a
+fully wired BDMV (`make_bdmv_fs`), not the bare `make_min_fs` this used to
+use. `make_min_fs` lays no STREAM/CLIPINF, so the play item's `.clpi` read
+now fails and the title drops — which is correct behaviour for an
+unresolvable clip but has nothing to do with the 30-second boundary this
+test exists to pin. Wiring the clip keeps the test measuring exactly one
+thing.
+
+## make_bdmv_fs_ssif
+
+Full BDMV with a real Blu-ray 3D layout: `.ssif` files under
+`BDMV/STREAM/SSIF/<clip>.ssif` (note the SSIF subdirectory, unlike
+`make_bdmv_fs_ext`) plus a matching `.clpi` in CLIPINF. Resolving the SSIF
+is what latches `is_3d = true` in `parse_playlist`.
+
+## Test: parse_playlist_fmts_clip_resolves_extent
+
+AACS 2.1: the feature clip is `00001.fmts`, NOT `.m2ts`. The
+`CLIP_STREAM_EXTS` fallback in `parse_playlist` must still resolve the
+physical extent — before the fix the hard-coded `.m2ts` path errored,
+yielding empty extents (a silent empty rip and 0 encrypted samples for key
+resolution). Size still comes from the `.clpi`, which parses regardless.
+
+## Test: parse_playlist_dedups_repeated_clip_extents_and_size
+
+THE 0.31.0 DEDUP PATH. A playlist that references the SAME clip_id from
+multiple PlayItems (seamless split / looped segment) must count the
+physical extents and packet bytes exactly once — mux reads extents in
+order, so a duplicate would mux the A/V twice and inflate `size_bytes`
+(bluray.rs: `first_ref = seen_clips.insert(...)` gates both `total_size +=`
+and the `extents.push`). Per-PlayItem Clip entries are still recorded for
+both.
+
+## Test: parse_playlist_missing_clpi_yields_no_title
+
+A clip whose `.clpi` is missing must yield no title.
+
+This test used to assert the opposite — a title with `size_bytes == 0` and
+empty extents — and its docstring quoted the buggy control flow ("bluray.rs
+only fetches extents inside the `if let Ok(clpi_data)`") as if it were the
+specification. It was blessing the defect: the title's `duration_secs` is
+summed from the PlayItems before the clip is resolved, so the returned
+title advertised the movie's full runtime while carrying none of its
+bytes, and the discarded error meant not one log line said so. That is the
+flagship failure class of this crate — a failure that looks like success —
+reached through an ordinary missing or scratched CLIPINF file.
+
+The correct behaviour is the same as for a clip whose extents cannot be
+resolved (see `parse_playlist_unreadable_clip_icb_yields_no_title`): drop
+the title and log the read's own error code.
+
+That last clause is now asserted, not merely asked for. The site's comment
+insists on `e.code()` because a missing `.clpi` (E6003), a scratched one
+(E6000) and a malformed one (E6002) are different populations, but nothing
+checked it: putting a literal back compiled and passed. Mutation: `"E6017"`
+(or any fixed code) in place of `"E{}", e.code()` fails here, and so does
+dropping the warn entirely — a silent drop is the same invisible title
+loss this test was written for, one step later.
+
+## Test: parse_playlist_unrecorded_extent_yields_no_title
+
+A clip stream whose ICB declares an UNRECORDED (ECMA-167 4/14.14.1.1
+type-1) extent must not yield a title at all.
+
+The extent is allocated to the file but was never written, so the file's
+content there is zeros while the media holds whatever was left at those
+sectors. Neither answer a `(lba, sector_count)` read plan can give is true
+— reading it splices undefined sectors into the rip as content, dropping
+it slides every later extent's byte space — so the title is refused rather
+than mis-ripped. This fixture is the shape a crafted disc uses to get such
+a range into a title's extent list.
+
+(The `sectors > 0 && lba > 0` filter below the resolver stays as defence in
+depth; a zero-length AD is only reachable as an unrecorded descriptor,
+since a zero-length TYPE 0 one terminates the AD list.)
+
+## Test: parse_playlist_unreadable_clip_icb_yields_no_title
+
+An unrecorded extent was never the only way a clip fails to resolve.
+
+RED BEFORE GREEN: this fixture gives the .m2ts an ICB whose descriptor tag
+is neither 261 nor 266, so `file_extents` returns `DiscRead` — the same
+variant a scratched sector under a real clip's ICB produces, which is the
+ordinary way this happens on real media. Before the fix only
+`UdfUnrecordedExtent` set the drop flag, so this fell through to the "file
+absent" path and `parse_playlist` returned a title: full declared duration
+from the play item, `total_size` already counted from the .clpi, and zero
+extents — a movie advertising its runtime with the content missing, and
+not one log line. The clip must drop the title exactly as an unrecorded
+extent does.
+
+## Test: parse_playlist_logs_a_non_absence_ssif_failure_the_m2ts_fallback_hid
+
+A non-absence SSIF failure that the `.m2ts` fallback then papers over must
+be logged, with its own code.
+
+`unresolved` had exactly one reader — `if let (None, Some(code))` — so a
+code recorded for `/BDMV/STREAM/SSIF/<clip>.ssif` was thrown away whenever
+the fallback succeeded. The disc here IS a 3D disc: the SSIF is present and
+carries both eyes, and only its ICB is unreadable (a scratched sector, the
+ordinary way this happens). The title shipped base-view 2D at rc=0 with
+`is_3d` false and not one log line, so the operator's rip is silently
+missing the dependent view and the journal cannot tell this disc apart
+from one that was only ever 2D.
+
+The title is deliberately still returned — the base view resolved, so
+refusing would trade a degraded rip for no rip. The defect being fixed is
+the silence, not the fallback.
+
+Mutations this catches: deleting the new `(Some(_), Some(code))` arm, or
+restoring the `if let (None, Some(code))` shape, leaves no event to find;
+logging a fixed code instead of `e.code()` fails the code assertion;
+making the arm `return Ok(None)` fails the title assertion.
+
+## Test: parse_playlist_id_falls_back_to_zero_when_suffix_is_not_mpls
+
+A filename that is long enough (>= 5 bytes) but does NOT end in ".mpls"
+must NOT have its last 5 bytes stripped — the whole string is handed to
+the numeric parse instead, which fails and falls back to playlist_id 0
+(bluray.rs `filename.len() >= 5 && filename[len-5..].eq_ignore_ascii_case(".mpls")`).
+
+## Test: scan_bluray_titles_skips_non_mpls_extension_file
+
+A non-directory PLAYLIST entry whose name does NOT end in ".mpls" must be
+skipped even though its content parses as a perfectly good (long) MPLS
+playlist — extension gating, not content sniffing, decides eligibility
+(bluray.rs `!entry.is_dir && entry.name...ends_with(".mpls")`).
+
+## HaltingReader
+
+A `SectorSource` that fails every read in `halt_range` with
+`Error::Halted` — exactly how a live drive behaves once the operator
+presses Stop: `Drive::checked_exec` fails every SCSI command with `Halted`
+from then on, and `Drive::read` deliberately preserves the variant. Reads
+outside the range still succeed, so a test can aim the cancel at one
+structure and leave the scan far enough along to have something to
+truncate.
+
+## Test: halted_playlist_read_is_not_reported_as_a_shorter_disc
+
+A Stop on a live drive never touches `ScanOptions::halt`: `Drive` has its
+own flag and `checked_exec` fails every SCSI command with `Error::Halted`
+once it is set. The Blu-ray enumerator must not swallow that into a
+successful scan.
+
+RED BEFORE GREEN: with the propagation reverted this returned
+`Ok([00800])` — the `if let Ok(mpls_data)` skipped the cancelled read of
+00801.mpls, the loop ended, and a half-enumerated disc came back at
+success. One title from a two-title disc is indistinguishable from a disc
+that genuinely holds one title, and the caller caches and rips from it.
+
+The halt lands on the second playlist deliberately: it is the last
+iteration, so nothing after it would poll a flag — only propagating the
+read's own error catches it.
+
+## Test: halted_clpi_read_is_not_accounted_as_an_unresolvable_clip
+
+The same cancel landing on a `.clpi` read must not be classified as an
+unresolvable clip either.
+
+RED BEFORE GREEN: with the `Err(Error::Halted)` arm removed from the
+CLIPINF match, the cancel fell into the generic "clip could not be
+resolved" arm, which logs a disc-defect code and drops the title —
+accounting an operator Stop as a scratched disc, and (in the scan loop)
+dropping every remaining playlist in turn for a truncated `Ok`. With the
+fix the cancel is propagated with its own variant intact.
+
+## Test: halted_extent_resolve_is_not_a_title_missing_its_clip
+
+And the same cancel landing on `file_extents` — the clip's ICB, not its
+CLIPINF — must propagate too.
+
+RED BEFORE GREEN: `note` used to exempt `Halted` from the unresolved
+classification (correctly — a cancel is not an authoring hole) but had no
+way to propagate it, so the resolver simply produced no extents and
+`parse_playlist` returned a title with the clip's runtime counted, its
+`size_bytes` counted from the .clpi, and zero bytes behind it. Measured
+with the propagation reverted: `Ok(Some((768000, [])))` — the flagship
+defect shape, wearing a cancel.
+
+## Test: read_meta_title_ignores_non_xml_file_regardless_of_content
+
+A non-.xml file must be ignored even if its content looks like a valid
+meta XML (contains a `<di:name>`) — extension gating, not content
+sniffing, decides eligibility (bluray.rs `!e.is_dir &&
+e.name...ends_with(".xml")`).

docs/bounded.md

@@ -0,0 +1,61 @@
+# `src/io/bounded.rs` — bounded-syscall primitive
+
+## Why this exists
+
+[`crate::halt::Halt`] is cooperative: callers poll `is_cancelled()`. It
+cannot reach inside a syscall the kernel currently owns the thread for —
+`libc::sync_file_range`, `libc::fsync`, `File::write` on NFS, and so on.
+`/api/stop` from autorip therefore can't unstick a thread sitting in
+such a syscall.
+
+`bounded_syscall` is the escape hatch: it runs `op` on a fresh worker
+thread, then `recv_timeout`s on a rendezvous channel for the result.
+The wait is broken into ~250 ms slices so the calling thread can poll
+the supplied `Halt` in between. If the deadline elapses or the halt
+fires, the worker is intentionally leaked — the syscall will unwind
+whenever the kernel decides, or at process exit, but the caller is
+free to fall back to a degraded code path (skip the sync, log loudly,
+etc.).
+
+## Trade-offs
+
+- **Thread per call.** Cheap (`std::thread::spawn` is < 100 µs on
+  Linux/macOS), but not free. Use on coarse-grained finalisation
+  syscalls (`sync_all`, `sync_file_range(WAIT_AFTER)`), not on hot
+  inner-loop writes.
+- **Leak on timeout.** A wedged syscall keeps a kernel slot and a
+  user-space thread around for the rest of the process's life. Bounded
+  by the number of independent rip/mux sessions, which is one per
+  disc. The alternative — trapping the caller forever — defeats the
+  entire purpose of `/api/stop`.
+- **Halt granularity ~250 ms.** Halt observation is not instant; it's
+  the worst-case latency of the `recv_timeout` slice. Good enough for
+  human-driven stop requests; not suitable for hard real-time
+  deadlines.
+
+## Single source of truth
+
+Do NOT inline this pattern. Every blocking-syscall wrapper in the rip
++ mux pipeline calls this helper, so changes (e.g. swapping the
+channel impl, adjusting the poll slice, adding metrics) land in one
+place.
+
+## Platform
+
+Pure `std::thread` + `std::sync::mpsc`. No `cfg(target_os)` needed
+here — the helper itself is platform-agnostic. Callers that wrap
+Linux-only syscalls (`sync_file_range`) still need their own
+`#[cfg(target_os = "linux")]` gates; this helper does not.
+
+## `bounded_syscall` contract details
+
+- `halt` is polled at `POLL_INTERVAL` granularity. Pass `None` for
+  callers that don't (yet) have a halt token plumbed through —
+  behaviour degrades to deadline-only, matching the 0.20.5
+  `wait_after_with_timeout` shape this helper generalises.
+- `op` returns `R: Send + 'static`. The closure must own everything it
+  touches because it may outlive this call (timeout / halt cases).
+- On `Halted` / `Timeout` the worker thread is intentionally leaked:
+  the syscall will unwind whenever the kernel decides, or when the
+  process exits. The calling thread is never trapped inside a kernel
+  call.

docs/byte-prefetcher.md

@@ -0,0 +1,111 @@
+# `byte_prefetcher` — design notes and test rationale
+
+`BytePrefetcher` (`src/io/byte_prefetcher.rs`) is the `std::io::Read`
+analogue of `crate::sector::PrefetchedSectorSource`. It spawns a
+producer thread that fills a bounded pool of `Vec<u8>` chunks from the
+underlying reader and ships them through a channel; the consumer pulls
+filled chunks, uses them, and sends the empty `Vec<u8>` back through a
+recycle channel so the producer can re-fill in place. Result: zero
+allocations and zero cross-thread frees in the steady-state hot loop.
+
+This is the byte-stream half of the freemkv mux highway —
+`BytePrefetcher` feeds `crate::mux::demux_thread::DemuxThread` for
+`m2ts://` (the only in-tree caller today, via `crate::mux::resolve`),
+and works for any stream whose source is an `io::Read` rather than a
+`SectorSource`.
+
+## `PrefetchShell`
+
+Drop blocks the calling thread until the producer exits. To guarantee
+a prompt exit, drop the forward receiver and the recycle sender first
+so the producer observes channel disconnection (or cancel the `Halt`
+passed to `BytePrefetcher::new`, which the producer polls at
+`POLL_INTERVAL` granularity even while parked on a channel op).
+
+## Test coverage rationale
+
+- **`recycle_depth_is_forward_depth_plus_one`** — `RECYCLE_DEPTH` must
+  be one MORE than `FORWARD_DEPTH` per its own doc comment: the
+  producer needs at least one buffer to fill while the consumer holds
+  the other `FORWARD_DEPTH`-worth in flight. A `+` -> `*`/`-` mutation
+  on `FORWARD_DEPTH + 1` would under-size the recycle channel (e.g.
+  `FORWARD_DEPTH * 1 == FORWARD_DEPTH`, one short), which starves the
+  producer of a spare buffer.
+
+- **`into_channels_drop_releases_producer`** — the CRITICAL
+  regression: after `into_channels`, dropping the returned forward
+  receiver + recycle sender must let the producer observe
+  disconnection and exit, so dropping the `PrefetchShell` (which
+  joins the producer) returns promptly. With the old clone+forget the
+  leaked endpoints kept the producer blocked and this join hung
+  forever.
+
+- **`delivers_all_bytes_in_order_across_chunks`** — CORE CONTRACT: the
+  prefetcher must deliver every source byte, in order, exactly once —
+  never silently truncate or duplicate. Source is 5000 bytes; chunk
+  size 1024 forces multiple chunks (4 full + 1 short of 904). The
+  reassembled stream must equal the source. Mutation: replacing
+  `buf.truncate(n)` with a no-op would over-report bytes on the final
+  short read and this fails.
+
+- **`short_read_truncates_to_actual_length`** — a reader that returns
+  fewer bytes than requested per call must NOT leave stale tail bytes
+  in the delivered chunk. Cursor over 10 bytes with a 4096 chunk
+  yields a single 10-byte chunk; the consumer must see exactly 10
+  bytes, not 4096. Grounds `buf.truncate(n)`. Mutation: delete the
+  truncate and the chunk would carry 4086 zero bytes of padding,
+  failing the length assert.
+
+- **`empty_source_yields_clean_eof_no_batches`** — EOF semantics: an
+  empty source (Cursor over `[]`) yields `read() == Ok(0)` on the
+  first call, which the producer treats as EOF and returns, dropping
+  tx. The consumer sees RecvError (zero batches), NOT an Err batch and
+  NOT a zero-length Ok batch. Grounds the `Ok(0) => return` arm.
+  Mutation: changing `Ok(0) => return` to `Ok(0) => continue` would
+  spin forever (test times out).
+
+- **`read_error_is_propagated_as_err_batch`** — a reader that fails
+  mid-stream must surface the `io::Error` as an `Err` batch on the
+  forward channel, not swallow it. We deliver one good chunk then an
+  error. The consumer must see the good bytes followed by the error.
+  Mutation: changing `let _ = tx.send(Err(e)); return;` to a plain
+  `return` would drop the error silently and this fails.
+
+- **`read_panic_surfaces_as_err_batch_not_clean_eof`** — PANIC
+  propagation: a reader that PANICS mid-stream must NOT be read as a
+  clean EOF at the demux boundary. The producer's `catch_unwind` sends
+  an explicit `Err` sentinel before the thread unwinds, so the
+  consumer sees the good bytes followed by an error batch — never a
+  silent truncation. Without the `catch_unwind` the panic would just
+  drop `tx`, the consumer would see RecvError (== clean EOF) and the
+  partial output would be finalized as if complete.
+
+- **`recycled_buffer_carries_no_stale_tail`** — recycle-buffer reuse
+  must NOT leak stale bytes between chunks of different lengths. After
+  a full chunk, a short read reuses the same recycled buffer; the
+  regrow-then-truncate sequence must yield only fresh bytes. Verified
+  by reassembling the full stream. Source: 8 bytes of 0xAA + 3 bytes
+  of 0xBB, with chunk_bytes=8 → chunk0 = 8×0xAA, chunk1 = 3×0xBB.
+
+- **`exact_multiple_length_no_trailing_empty_batch`** — exact-multiple
+  boundary: when the source length is an exact multiple of
+  chunk_bytes, the final non-empty chunk is followed by an `Ok(0)` EOF
+  read, NOT a spurious empty Ok batch. 12 bytes with chunk_bytes=4 →
+  three 4-byte chunks then clean EOF. Total bytes must equal 12 and no
+  zero-length batch may appear.
+
+- **`drop_finite_prefetcher_joins_cleanly`** — dropping the
+  `BytePrefetcher` directly (without `into_channels`) must join the
+  producer cleanly when the source is finite. The producer reaches
+  EOF, drops tx, and exits; Drop's join returns. Grounds the
+  `BytePrefetcher` `Drop` impl. Mutation: removing the `Ok(0) =>
+  return` EOF exit would hang this join.
+
+- **`drop_endless_prefetcher_joins_cleanly`** — regression: dropping a
+  `BytePrefetcher` directly (without `into_channels`) with an ENDLESS
+  source must not deadlock. Before the fix, `Drop` joined the producer
+  while `rx`/`recycle_tx` were still alive (sibling field drop order),
+  so the producer filled the depth-2 forward channel and then spun in
+  `send_timeout` forever (rx never drained, halt=None). The fix drops
+  `rx`+`recycle_tx` BEFORE the join so the producer sees
+  `SendTimeoutError::Disconnected` and exits.

docs/class-reader.md

@@ -0,0 +1,48 @@
+# `labels::class_reader`
+
+Hand-rolled JVM `.class` file reader, tailored to the subset needed for BD-J
+label extraction (Deluxe / dbp / similar frameworks). Implements JVMS §4
+(class file format) and §6 (bytecode) only as far as: constant pool,
+methods, the `Code` attribute, and a non-allocating bytecode iterator.
+
+No external deps beyond `std`. No `unsafe`. No panics on malformed input —
+every parse fault is a typed `Error`. This is shared infrastructure for any
+label parser that needs structured access to `.class` files inside a
+`/BDMV/JAR/<x>.jar`.
+
+## `ConstantPool::from_entries`
+
+Test-only constructor — builds a constant pool directly from a vector of
+entries. Real callers go through `ClassFile::parse`, which builds this from
+class-file bytes. Used by parser unit tests (e.g. `labels::deluxe`) that
+need to exercise bytecode walkers against synthetic class fixtures without
+hand-rolling valid `.class` byte buffers.
+
+Caller is responsible for: prepending a `CpInfo::Empty` at index 0 (the
+spec-reserved slot), and inserting a `CpInfo::Empty` after each Long/Double
+entry (the 2-slot quirk).
+
+## `decode_modified_utf8`
+
+Decodes JVM "modified UTF-8" (JVMS §4.4.7). Practically identical to
+standard UTF-8 for the BMP-printable subset seen in label strings, but with
+two notable deviations:
+
+- U+0000 is encoded as the two-byte sequence `0xC0 0x80`, not as `0x00`.
+- Supplementary characters (U+10000..) are encoded as a UTF-16 surrogate
+  pair, each surrogate emitted as 3-byte modified UTF-8.
+
+For label data (mostly ASCII / Latin-1 / CJK in BMP), the simple
+implementation here covers everything we'll encounter. The `0xC0 0x80` →
+U+0000 case is tolerated explicitly; supplementary characters would need
+surrogate-pair stitching, but no label-relevant string uses them.
+
+## `Reader::slice` overflow test
+
+`Reader::slice` takes an attacker-supplied length: a JVMS `u4`
+`attribute_length` / `code_length` (§4.7, §4.7.3) or a `u2` Utf8 length
+(§4.4.7). Adding it to `pos` without a wrap check panics on overflow in
+debug and, in release, wraps to a small end offset that slips past the
+bounds check and then panics inside the slice index. Both are panics
+escaping a parser whose whole input is untrusted disc bytes; the contract
+is an EOF error.

docs/clpi-audit.md

@@ -0,0 +1,18 @@
+# CLPI vs MPLS cross-validation diagnostic
+
+`src/labels/clpi_audit.rs` walks both per-clip CLPI program info and
+per-playlist MPLS STN tables, normalizes their stream lists by `(PID,
+language, coding_type)`, and classifies each PID into one of four
+buckets:
+
+1. **CLPI only** — a stream present in a `.clpi` ProgramInfo that no
+   playlist STN table references (orphan on disc).
+2. **MPLS only** — a stream a playlist references that no `.clpi`
+   ProgramInfo lists (indicates a parser disagreement).
+3. **Match** — both sources agree on coding_type and language.
+4. **Divergent** — both sources see the PID but disagree on
+   coding_type or language.
+
+`audit` returns a structured `ClpiVsMplsAudit` report. This is a
+diagnostic surface only; it does not feed the label-selection
+pipeline.

docs/clpi.md

@@ -201,6 +201,42 @@ The full ripping pipeline chains three parsers:
 
 The `Disc::scan()` method in `src/disc/mod.rs` orchestrates this: for each play item in each playlist, it loads the corresponding CLPI, calls `get_extents()` with the play item's in/out times, and collects the resulting sector ranges into the title's extent list.
 
+## ProgramInfo Section (Per-Stream Metadata)
+
+`parse_program_info` in `src/clpi.rs` reads per-stream (pid, coding_type,
+language, codec sub-fields) from the ProgramInfo section, per the Blu-ray
+Disc Read-Only Format Part 3 CLIPINF (CLPI) specification:
+
+```text
+ProgramInfo:
+  length: 4 bytes
+  reserved: 1 byte
+  num_programs: 1 byte
+  for each program:
+    spn_program_sequence_start: 4 bytes
+    program_map_pid: 2 bytes
+    num_streams: 1 byte
+    num_groups: 1 byte
+    for each stream:
+      pid: 2 bytes
+      stream_coding_info_length: 1 byte
+      stream_coding_info: (varies by coding_type)
+        coding_type: 1 byte
+        per-type bytes (see match arms in parse_program_info)
+```
+
+It returns `Vec::new()` on any structural mismatch — errors aren't
+propagated because the EP map is the primary CLPI output, and a corrupt
+program_info shouldn't break sector-range lookups.
+
+### Test fixture notes
+
+- `prog_info_start_zero_does_not_parse_header_as_program_info`: the
+  fixture is crafted so that parsing from offset 0 WOULD yield a stream
+  (num_programs at `[5]`, a second program header whose num_streams
+  byte at `[20]` is 1, then a well-formed stream record), so an empty
+  result can only come from the `prog_info_start > 0` gate in `parse`.
+
 ## References
 
 - BD-ROM Part 3, Section 5.5: Clip Information file format

docs/codec-mod.md

@@ -0,0 +1,79 @@
+# `src/mux/codec/mod.rs` — extended notes
+
+Relocated prose from doc comments in `mod.rs`, trimmed there to stay within
+the comment-guard's prose caps. Each `//`/`///` pointer in the source names
+the section here it corresponds to.
+
+## `Frame::discontinuity`
+
+Carried per-FRAME (not per-PES) because buffering parsers decouple the frame
+from the PES that carried the gap signal: MPEG-2 emits whole GOPs, H.264/HEVC
+lag one access unit behind the PES that produced them. A clean rip leaves
+every frame `false`; the flag is only ever set on the degraded/conceal path
+(P3/B1), when a frame's data begins after packets the demuxer never received
+— an undecryptable unit concealed as NULL-TS upstream, or a continuity break
+in a damaged source.
+
+## Drop-on-undecodable policy across codecs ("clean muxes always")
+
+- **Audio with independent access units** (DTS, AC-3/E-AC-3, …) gates each AU
+  through a per-codec corruption check and drops the ones that fail, keeping
+  A/V sync (a drop is a silence gap, never a shift) and logging every drop
+  via the shared `dropgate::DropTally`. DTS validates via its core-frame
+  header (ETSI TS 102 114); AC-3 uses its native frame CRC.
+- **LPCM is excluded on purpose**: raw PCM carries no framing or integrity
+  data, so a corrupt sample is indistinguishable from a quiet one — there is
+  nothing to detect, so nothing can be honestly dropped.
+- **Video is excluded on purpose**: H.264/HEVC/MPEG-2/VC-1 are inter-frame
+  predicted, so dropping one frame corrupts every frame that references it
+  until the next keyframe. Video instead resyncs at GOP/IDR boundaries (the
+  ResyncGate) and lets the decoder conceal — a fundamentally different model
+  than per-frame audio dropping.
+- TrueHD/MLP, FLAC, MP2/MP3 and AAC-ADTS also gate undecodable frames via a
+  `DropTally` (poison/drop-forward for MLP's inter-AU restart state on a
+  major-sync boundary; CRC/sync-verdict drops for the passthrough codecs).
+
+## `codec_private()` — why "absent" is the only truthful answer for some parsers
+
+A codec parser's `codec_private()` feeds `DiscStream::codec_private`, which
+the MKV muxer turns directly into the track's `CodecPrivate` element (RFC
+9559 §5.1.4.1.24): `Some(bytes)` writes an element holding exactly those
+bytes, `None` omits the element entirely. The two are NOT interchangeable —
+a zero-length `CodecPrivate` asserts that the codec's initialisation data IS
+empty, which is not true of any codec, and a one-byte one asserts a config no
+decoder can parse.
+
+The gating parsers (ADTS, MPEG audio, FLAC) and the passthrough parser
+extract no configuration at all: they validate and forward frames whose
+configuration is carried in band (ADTS headers, MPEG-1 audio frame headers,
+FLAC frame headers) or supplied by the source container. Having derived
+nothing, the only truthful answer they can give is "absent" — any `Some`
+would be a value they invented. Nothing else in the test suite distinguished
+the two, so each of these impls could have returned a fabricated `Some` and
+produced a malformed track header unnoticed.
+
+## `provenance_guard` test module
+
+Every emitted frame must carry the source byte offset of the packet it came
+from. That invariant held only for video for as long as it existed: `dts`,
+`ac3`, `adts`, `truehd`, `pgs`, `dvdsub`, `flac`, `lpcm`, `mpegaudio` and the
+passthrough parser all built frames with `source: None`, so a multi-clip
+title could not place audio or subtitles by byte and fell back to inferring
+the clip from timestamps — which is what made branched titles run minutes
+long.
+
+Nothing asserted it, so nothing caught it. Finding it took a brace-balanced
+scan of the tree by hand, which also turned up five sites a regex had
+missed. `provenance_guard` is that scan, as a test.
+
+### `code_only` / `frame_literals` design
+
+`frame_literals` walks `Frame { .. }` literals with balanced braces. A regex
+cannot do this — `Frame` blocks contain nested braces (`coding: Some(..)`,
+closures) and a non-greedy match stops at the first `}`, which is how five
+sites survived the first pass.
+
+`code_only` strips line comments before scanning. A comment that MENTIONS
+`source: None` is prose, not a construction — this guard's own doc comment
+tripped it on the first run, which is the same mistake as grepping a file
+and matching its commentary.

docs/coding.md

@@ -0,0 +1,17 @@
+# `src/mux/codec/coding.rs`
+
+## Spec references
+
+ITU-T H.273 (CICP code points, shared elsewhere), ISO/IEC 13818-2 §6.3.10
+(MPEG-2 picture coding extension: `top_field_first`, `repeat_first_field`,
+`progressive_frame`), RFC 9559 §5.1.4.1.28 (Matroska `FieldOrder` element
+0x9D).
+
+## HDR10 unit scaling
+
+`Hdr10Metadata` values are stored in their raw SEI integer units (not yet
+scaled to the Matroska float domain); the muxer applies the H.265 → Matroska
+unit conversion at emit time so the scaling lives in exactly one place.
+
+Spec: Rec. ITU-T H.265 D.2.28 (Mastering Display Colour Volume, payloadType
+137) and D.2.35 (Content Light Level Info, payloadType 144).

docs/consts.md

@@ -0,0 +1,11 @@
+# `consts::coding_type` — spec citations
+
+`coding_type` is one registry used in two places that share the same value
+space: the MPEG-TS PMT `stream_type` (ISO/IEC 13818-1 Table 2-34) and the
+Blu-ray STN/CLPI `stream_coding_type` (BD-ROM Part 3).
+
+The standardized video codes (`0x02`, `0x1B`, `0x24`) are ISO assignments
+(ISO/IEC 13818-1 Table 2-34); `0xEA` (VC-1) is a BD-ROM convention in the ISO
+user-private range. The `0x80..=0xA2` audio/graphics codes also sit in the
+user-private range and follow the Blu-ray Disc Association / ATSC A/52
+convention.

docs/crc.md

@@ -0,0 +1,14 @@
+# CRC helpers (`src/mux/codec/crc.rs`)
+
+## `crc16_mlp` reversed byte order
+
+MLP's checksum is the "reversed" scheme. `crc16_mlp` emits its two bytes in
+the OPPOSITE order to a standard little-endian CRC readout, so the caller
+swaps them back and compares against the stored trailer word read
+LITTLE-endian — see `truehd::mlp_major_sync_crc_ok`, which is authoritative.
+
+Comparing big-endian instead is precisely the bug that function was fixed
+for: it could never validate a real extended major sync, so whole TrueHD
+tracks were dropped silently. This comment used to prescribe exactly that,
+and to point at a `truehd::mlp_major_sync_ok` that does not exist.
+Verified against real MLP/TrueHD bitstreams (225/225 major-sync AUs).

docs/criterion.md

@@ -0,0 +1,87 @@
+# `src/labels/criterion.rs` — internal notes
+
+## `assign_stream_numbers`
+
+Assign a 1-based stream number per `StreamInfo`, parallel to `infos`.
+
+A stream mapped in `playbackconfig.xml` (`stream_map`) keeps its
+mapped number. Streams with no mapping (absent or incomplete
+`playbackconfig.xml`, or an unmatched `StreamInfo_ID`) are numbered
+1-based per type — but the fallback counter SKIPS any number already
+claimed via the map, so a synthesized number can never collide with a
+map-assigned one. (Both numbering domains are 1-based per type, and
+`apply_labels` matches on `(type, stream_number)`, so a collision
+would mislabel tracks.)
+
+Returns `None` when the 1-based stream-number space is exhausted —
+every number in `1..=u16::MAX` for that type is either already
+claimed by the map or already synthesized. That is unreachable on
+real media: the BD STN_table carries at most 32 primary audio and 32
+PG streams per playlist, so the 65535-wide space leaves >2000x
+headroom. It IS reachable from a crafted `streamproperties.xml`
+listing >65535 stream entries, and the only correct answers there are
+"fail the parse" or "emit colliding numbers"; we fail.
+
+The skip search is bounded by the numbering space itself: a `u16`
+`saturating_add` here parked the counter at `u16::MAX` forever
+whenever the map also claimed `u16::MAX`, turning an overflow guard
+into a hang that `apply()`'s `catch_unwind` cannot interrupt. The
+counters are therefore widened to `u32` so the skip loop strictly
+increases toward a fixed ceiling (guaranteeing termination) and
+exhaustion is reported rather than absorbed.
+
+## Test: immunity pin, section-boundary half
+
+Covers `an_unterminated_stream_element_shortens_the_list_it_cannot_extend_it`.
+
+`parse_stream_infos` emits one `StreamInfo` per `*StreamInfos` element
+unconditionally — no filter, no `continue` — so an element whose
+fields are missing or unrecognized still occupies its position, and
+`assign_stream_numbers` still spends a number on it.
+
+That is the property that keeps this parser out of the failure mode
+where a skipped entry pulls every later label one stream forward. It
+is load-bearing for the fallback path specifically: with no
+`playbackconfig.xml` the numbers come purely from position in this
+list, so dropping an element there would shift the rest.
+
+Mutation: skip elements with an empty `ID`/`LangInfoID` → the two
+real audio streams renumber to 1 and 2.
+
+Each stream here is one closed XML element, and every field is read
+out of `&text[start..end]` — the range `xml::find_element` returned —
+so one element can never absorb the next one's fields, however the
+document is malformed around it. Contrast the flat-string walk in
+pixelogic, where a section whose end marker is missing keeps
+consuming entries as STN slots.
+
+The missing-boundary case fails closed. An element with no close tag
+of its own ends at the NEXT close tag, so it absorbs the element
+behind it — the list comes back SHORTER. It cannot come back longer:
+nothing outside a returned range is ever read as a stream, and
+`find_element` yields `None` rather than a range running to EOF when
+no close tag exists at all. A malformed document can cost this parser
+a slot; it can never invent one.
+
+Mutation: read fields from the document rather than the element's
+range, or let a close-less element run to EOF → the trailing elements
+re-enter the list as extra streams.
+
+## Test: `exhausted_numbering_terminates_instead_of_looping`
+
+A crafted `streamproperties.xml` can drive the fallback counter to
+the top of the 1-based u16 stream-number space and then present one
+more unmapped stream whose successor number is also claimed by the
+map.
+
+This must TERMINATE. The bound is the numbering space itself, so the
+assertion is on the spec-derived exhaustion behaviour (`None`), not
+on any tunable constant. Run on a worker thread with a deadline so a
+non-terminating loop fails the test in 20 s instead of hanging CI.
+
+## Test: `full_u16_numbering_space_is_usable_and_unique`
+
+The whole 1-based u16 space must remain usable: 65535 unmapped audio
+streams get 65535 distinct numbers with no panic and no wrap. The
+literals here are the JVMS-independent, spec-derived size of a u16
+1-based numbering domain, not a tunable cap.

docs/css-keyless.md

@@ -0,0 +1,245 @@
+# CSS keyless title-key recovery (`src/css/keyless.rs`)
+
+## The cipher this attacks
+
+The content descrambler ([`super::lfsr::descramble_sector`]) seeds its two
+LFSRs **directly** from `key = title_key XOR sector_seed` (seed =
+`sector[0x54..0x59]`): LFSR1 from key/seed bytes 0-1, LFSR0 (24-bit) from
+bytes 2-4 with the pre-conditioning `r0 = r0*2 + 8 - (r0 & 7)`, and each body
+byte recovered as `plain = TAB1[cipher] ^ (keystream & 0xff)`. There is no
+title-key mangling on the content path, so the recovery is a single inversion
+of the sector cipher.
+
+## The attack
+
+1. **Known plaintext → keystream.** Because descramble applies TAB1 to the
+   ciphertext, the per-byte keystream is `TAB1[cipher[i]] ^ plain[i]`.
+2. **Brute the 16-bit LFSR1 seed.** For each of 2^16 seeds, run LFSR1
+   forward; for the first four steps deduce the LFSR0 output bytes from the
+   keystream (carry-tracked), reconstructing LFSR0's state. For the next six
+   steps clock LFSR0 normally and check it reproduces the keystream — a wrong
+   LFSR1 seed fails fast.
+3. **Back-clock LFSR0.** Run four backward steps (each a 256-way search for
+   the byte shifted in) to reach the initial state, then undo the
+   `r0*2 + 8 - (r0 & 7)` pre-conditioning to recover key[2..5].
+4. **XOR back the seed.** `key[0..5] ^= sector_seed[0..5]`.
+
+Known plaintext for step 1 comes from the longest periodic run in the
+cleartext `sec[0x00..0x80]`, assumed to continue into the encrypted region at
+0x80.
+
+## `recover_title_key_from_plain`
+
+Core of the recovery. `crypted` is the ciphertext starting at sector byte
+0x80; `decrypted` is the matching known plaintext; `seed` is
+`sector[0x54..0x59]`. On success returns the recovered 5-byte title key;
+`None` if no LFSR seed reproduces the keystream. At least 10 bytes of
+`crypted`/`decrypted` are required (the cipher is iterated 10 times: 4 to
+reconstruct LFSR0, 6 to validate).
+
+## `attack_crib`
+
+Scans the clear header `sec[0x00..0x80]` (never scrambled) for the longest
+run that repeats with a cycle length in 2..0x2F. If the run is long enough
+(`plen > 3` and at least two full cycles), the plaintext at 0x80 is taken to
+be that periodic run continuing forward. Returns `None` for an unscrambled
+sector or one with no usable run — such a sector can be neither cracked nor
+key-validated, only descrambled with an externally-cached key.
+
+The header is untouched by `descramble_sector`, so the crib is identical
+before and after descramble: the decrypt path uses it as a per-sector
+"did the cached key descramble correctly?" oracle (the predicted plaintext
+must reappear at 0x80), and the cracker uses it as its known plaintext.
+
+## Tests
+
+### `synth_sector`
+
+Builds a synthetic scrambled sector for a given title key and seed, with
+`plain` placed as the plaintext at byte 0x80, scrambled with EXACTLY the
+cipher `descramble_sector` inverts. Returns
+`(scrambled_sector, full_plaintext_body)`.
+
+### `synth_periodic_sector`
+
+Builds a synthetic scrambled sector whose CLEARTEXT (0x00..0x80) ends in a
+periodic run that continues into the encrypted region — the case
+`crack_title_key` is designed to crack.
+
+### `recover_round_trips_known_keys`
+
+MANDATORY round-trip (Task C.1): synthesize a scrambled sector for a known
+(title_key, seed), then assert `recover_title_key` returns a key that
+descrambles the body back to plaintext. CSS title-key recovery is
+well-defined up to keys that scramble identically; we assert the full body
+round-trips (the true correctness property), and additionally that the EXACT
+key is returned for the common case.
+
+### `descramble_matches_accepts_only_the_key_the_sector_was_scrambled_with`
+
+`descramble_matches` is the ONLY gate between the LFSR search and a key
+handed back to the caller: both `recover_title_key` and the crib-driven
+`crack_title_key_inner` return a candidate only if this says the key really
+descrambles the sector to the known plaintext. A body that always answered
+`true` would let the first spurious LFSR-seed match through as the title
+key — the ripper would then descramble the whole title with a key that opens
+nothing, producing garbage rather than a "no key" error.
+
+Pinned both directions: the genuine key is accepted, and EVERY key one bit
+away from it is rejected. The one-bit neighbours are the strongest form of
+wrong key — a gate that only rejects wildly different keys would still pass
+a near-miss out of the 2^16 seed search.
+
+### `descramble_matches_does_not_disturb_the_caller_s_sector`
+
+The gate is applied to a COPY: verifying a candidate must not modify the
+caller's sector. `recover_title_key` runs the gate and then hands the sector
+on to be descrambled for real — if verification descrambled in place, that
+second descramble would run over already-transformed bytes (and, worse, a
+rejected candidate would leave the sector corrupted).
+
+### `recover_rejects_a_sector_that_ends_inside_the_encrypted_region`
+
+A sector buffer that ENDS inside the encrypted region must be refused, not
+sliced. `recover_title_key` slices `sector[0x80..0x8A]` unconditionally
+after its length guard. The existing short-sector test uses
+`SECTOR_BYTES - 1`, which is still long enough for that slice to succeed —
+so the guard was never the thing producing the `None`, and dropping it (or
+weakening the `||` to `&&`, which a full-length crib satisfies) changed
+nothing observable. On a real short read this is an out-of-bounds panic on
+the rip thread.
+
+### `a_buffer_longer_than_one_sector_still_yields_its_key`
+
+A buffer LONGER than one sector is still one sector: both entry points read
+the first `SECTOR_BYTES` and must recover the key from it. Callers read DVD
+data in multi-sector blocks, so an over-long slice is the normal case, not
+an exotic one. A length guard that rejected it (`len > SECTOR_BYTES` instead
+of `<`) would make every block-read caller silently unable to crack
+anything.
+
+### `recover_accepts_more_than_ten_bytes_of_known_plaintext`
+
+`recover_title_key` accepts MORE than ten bytes of known plaintext, and uses
+all of it: the extra bytes tighten the `descramble_matches` gate. The
+ten-byte figure is a MINIMUM (the cipher is iterated ten times), not an
+exact requirement — a guard reading it as an upper bound would reject every
+caller that knows a longer crib.
+
+### `a_recoverable_sector_with_the_scramble_bits_cleared_is_still_refused`
+
+The scramble-flag gate on a sector whose BODY really is ciphertext. Both
+entry points refuse a sector with `sector[0x14] & 0x30 == 0`: an
+unscrambled sector has no title key to recover, and its bytes at 0x80 are
+already plaintext. Every prior test of this gate used an all-zero or
+all-`0x11` sector, where the recovery would have found nothing anyway — so
+widening the mask test (`&` to `|`, which makes it true for EVERY flag byte)
+produced the same `None` and went unseen.
+
+Here the sector is genuinely scrambled and its key IS recoverable; only the
+cleared flag stands in the way. If the gate stops working, both functions
+start returning keys for sectors the disc says are in the clear.
+
+`attack_crib` carries its own copy of the same gate and is the one that
+actually stops the crack (`crack_title_key`'s is defensive duplication); it
+also doubles as the decrypt path's cached-key oracle.
+
+### `descramble_matches_forces_the_scramble_flag_on_its_own_copy`
+
+The gate must verify a candidate against the sector's CIPHERTEXT regardless
+of what the sector's own flag byte says. `descramble_matches` forces `0x10`
+on its copy precisely because `super::lfsr::descramble_sector` is a no-op
+when the scramble bits are clear — without that, verifying a
+scrambled-but-unflagged sector compares raw ciphertext against the crib, and
+every candidate key is rejected. Nothing exercised it: every fixture already
+had the flag set, where forcing the bit is a no-op.
+
+### `descramble_matches_compares_all_of_the_plaintext_and_no_more_than_the_sector`
+
+The gate compares the WHOLE supplied plaintext, clamped to the encrypted
+region. Two properties in one, because they are the two halves of
+`plain.len().min(SECTOR_BYTES - ENCRYPTED_START)`:
+
+- it must compare beyond the first sixteen bytes, or a key that opens only
+  the head of the crib is accepted; and
+- it must never compare past the end of the sector — a caller that knows
+  more plaintext than the 1920-byte encrypted region holds otherwise
+  indexes off the end of the buffer and panics.
+
+### `sector_with_trailing_run`
+
+Builds a sector whose clear header ends in a `period`-length repeating run
+of exactly `run_len` bytes immediately before 0x80. The run is anchored to
+ABSOLUTE sector offset (`sec[x] = pat[x % period]`), which is what makes
+"the run continues past 0x80" a statement independent of the code under
+test: the byte at `0x80 + i` of the underlying plaintext is
+`pat[(0x80 + i) % period]`. Everything before the run is `0x00` (the pattern
+bytes are all >= 0xD0, so the run cannot be extended backwards by accident),
+and the encrypted region is filled with `0xFF` — so a crib that reads past
+0x80 into "ciphertext" is immediately visible.
+
+### `attack_crib_predicts_the_periodic_run_continuing_past_0x80`
+
+KNOWN ANSWER: for a run of `run_len` bytes with period 5 ending exactly at
+0x80, the crib is the run continued forward — the same ten bytes for every
+run length, because the prediction depends only on the pattern and the
+phase, never on how many cycles happened to be visible. The short lengths
+are the load-bearing ones: at `run_len = 11` the crib window starts at 0x76
+and is only 10 bytes from the end of the header, so any drift in
+`plain_start`, in `cycles * best_p`, or in the `i % best_p` wrap reads the
+0xFF "ciphertext" instead of the run.
+
+### `attack_crib_refuses_a_run_shorter_than_two_cycles`
+
+A run of exactly ONE cycle (plus the trivial tail the detector counts) is
+not enough to predict forward: `attack_crib` requires at least two full
+cycles. Weakening that guard would let a one-off byte sequence be declared
+periodic and produce a confidently wrong crib — which the decrypt path uses
+as its "is my cached key still right?" oracle.
+
+### `attack_crib_refuses_a_buffer_shorter_than_a_sector`
+
+`attack_crib` indexes `sector[0x7f - j]` with no per-access bound, so its
+own length guard is the only thing between a short buffer and an
+out-of-bounds read. Nothing reached it: every caller-level test used a full
+sector, and the entry points' guards fire first.
+
+### `attack_crib_survives_a_header_that_is_periodic_to_offset_zero`
+
+A header that is periodic ALL THE WAY to offset 0 must not walk the
+backward scan off the front of the sector. The detector counts backwards
+from 0x7f while `j < 0x80`. On a fully periodic header the run never
+breaks, so `j` reaches 0x7f and the bound is the ONLY thing that stops it —
+one step further and `0x7f - j` underflows a `usize` and panics. A constant
+or fully-patterned 128-byte header is ordinary DVD data (padding, a run of
+zeros), not a crafted input, and every existing fixture had a
+filler/run boundary well before offset 0 that stopped the scan early.
+
+### `attack_crib_is_independent_of_the_encrypted_region`
+
+The crib is read from the CLEAR header only. A run that reaches 0x80 must
+predict from the header bytes, never from the encrypted region — the
+previously-fixed bug this function's doc comment records. Pinned by
+rewriting the encrypted region and requiring the crib not to move.
+
+### `recover_title_key_from_plain_refuses_fewer_than_ten_bytes_of_either_input`
+
+`recover_title_key_from_plain` unconditionally builds a 10-byte keystream
+buffer from `crypted[0..10]` and `decrypted[0..10]`, so its length guard is
+the only thing standing between a short slice and an index-out-of-bounds
+PANIC. Nothing reached that guard before: `recover_title_key` rejects
+`plain.len() < 10` at its own door and always hands on exactly ten
+ciphertext bytes, and `crack_title_key_inner` always passes a fixed
+`[u8; 10]` crib. The guard is a live contract for any future caller and was
+executed by no test at either boundary.
+
+### `recover_title_key_from_plain_xors_the_sector_seed_back_out`
+
+The seed XOR-back (`recover_title_key_from_plain`'s last step) is what turns
+the recovered LFSR key into the TITLE key: `key ^= sector_seed`. Pinned as a
+known answer across seeds that differ only in one byte — the same
+ciphertext/plaintext pair therefore must yield title keys differing in
+exactly that byte. Without this, a body that ORed the seed in (or dropped
+the step) still round-trips on any fixture whose seed is zero, and on the
+non-zero ones the failure looks like "no key found" rather than a wrong
+step.

docs/css-mod.md

@@ -0,0 +1,311 @@
+# `src/css/mod.rs` — extended notes
+
+Overflow detail relocated from doc comments in `src/css/mod.rs` (kept short
+there per the comment-guard caps). Function/item names below match the code.
+
+## `CSS_LOCKED_BAIL`
+
+The bus-auth read gate is global (all-or-nothing), so a run this long of
+`05/6F/03` (CSS-locked) reads means the gate is shut and nothing here is
+crackable — bail instead of grinding the full 50_000-sector budget. That
+grind is what made rc5 appear to hang on a wedged USB bridge.
+
+## `crack_key`
+
+Recovers the CSS title key with no keys, by scanning scrambled sectors and
+running the known-plaintext attack (see the `keyless` module). The crib comes
+from the periodic-run detector: a scrambled sector's cleartext region
+(bytes 0x00..0x80) often ends in a short-period repeating run (stuffing /
+constant fill); the attack assumes that run continues across the 0x80
+boundary into the encrypted region, giving the known plaintext the 2^16 LFSR
+recovery needs. Scans up to 50000 sectors across the extents and returns the
+first sector that yields a key — no player keys, no disc-key crack. Works on
+a live drive (after bus-auth unlocks reads) and on disc images alike.
+
+This convenience form runs to completion (no cancellation) and returns just
+the key; callers needing an operator-Stop / watchdog cancel, or the
+three-way `CrackOutcome` (to distinguish "unencrypted" from
+"encrypted-but-uncracked"), use `crack_key_outcome`, which takes a `halt`
+token.
+
+## `CrackOutcome`
+
+Distinguishes the three cases the bare `Option<CssState>` conflated (and
+which caused a silent-failure bug: scrambled-but-uncracked content was
+treated as "unencrypted" and muxed as plaintext garbage at exit 0):
+
+- `Cracked` — a scrambled sector yielded a title key.
+- `Unencrypted` — NO scrambled sector was seen across the scanned extents
+  (`is_scrambled_pack` never true): the content is genuinely plaintext, so
+  proceeding without a key is correct.
+- `ScrambledUncracked` — scrambled sectors WERE seen but no key could be
+  recovered (the recovery found no crackable crib, or the scrambled region
+  was unreadable). The content is encrypted; muxing it as plaintext would
+  emit garbage, so callers MUST surface a hard error instead of falling
+  through to "unencrypted" — the per-title `crate::error::Error::CssKeyMissing`
+  when it is ONE title's own re-crack that failed (skippable: a sibling VTS
+  may still crack), or the disc-level `crate::error::Error::CssNoDiscKey`
+  when it is the disc-wide scan (`Disc::css_error`, every title fails
+  identically).
+
+## `resolve_dvd_title_key`
+
+The SINGLE place every DVD read path obtains a title key, so the file-backed
+mux highway (`crate::build_iso_pipeline`) and the live-drive single-pass
+`crate::DiscStream` descramble a DVD identically ("reading is reading"). CSS
+keys are per-VTS and crackable from the scrambled data itself, so a
+`None`/MPEG-PS title cracks its own key here, in playback order over
+`extents`. Everything else is left untouched:
+
+- AACS keys (HD-DVD `.evo` is also MPEG-PS but arrives as `Aacs`) — no CSS.
+- a title that already carries a key — nothing to resolve.
+- a genuinely clear DVD (no scrambled sector) — stays `None`, a mux no-op.
+
+A scrambled-but-uncrackable title is a hard `crate::error::Error::CssKeyMissing`,
+never a silent scrambled-passthrough mux. That code is the PER-TITLE one
+(`error::is_skippable_title_stub`), which is correct here: this function
+cracks ONE title's own extents, and another VTS on the same disc may still
+yield its key, so an all-titles rip skips this title and finishes the rest.
+The whole-disc failure is `crate::error::Error::CssNoDiscKey`, raised by
+`Disc::ensure_decryptable_keys` from the scan's `css_error`.
+
+## `crack_key_scan` (private)
+
+Tracks a `saw_scrambled` flag so a scrambled-but-uncracked disc is
+distinguished from a genuinely-unencrypted one (the `crack_key` `Option`
+wrapper collapses both to `None` via `CrackOutcome::into_state`).
+
+## `descramble_sector`
+
+A no-op unless the sector is a scrambled MPEG-2 PS PACK. The pack start code
+is checked, not just the byte 0x14 flag bits, for the same reason
+`descramble_region` checks it: 0x14 only means "scrambling control" inside a
+pack, and in an IFO it is whatever that format stores there. A real
+`VIDEO_TS.IFO` sector holds 0x15 there while starting `00 26 00 00`;
+descrambling it destroyed 1912 of its 2048 bytes, and because that sector
+carries TT_SRPT the disc enumerated 38 titles while an image decrypted from
+it enumerated 10, silently, at exit 0.
+
+This function has no callers inside the crate, but the module-level example
+prescribes it — so the crate's own documented guidance led straight into
+that defect. Making the guard part of the function, rather than something
+each caller must remember, is what keeps the safe path the easy one.
+
+## `descramble_region`
+
+Descrambles a whole CSS buffer in place, re-cracking the title key on a VOB
+region boundary. `title_key` is a CACHE of the last crack, not a fixed disc
+key: it changes per VTS/VOB region, so it is validated on every scrambled
+sector and re-cracked on a miss (the standard on-demand per-region rekey).
+
+This CSS key acquisition is intrinsic to the cipher — CSS has no external key
+source, the ONLY way to a title key is cracking the data — so it lives with
+the CSS primitives and runs inside `decrypt::decrypt_sectors` (a public,
+self-contained CSS decrypt), NOT at the post-decrypt recovery seam that AACS
+key-fetch and FMTS segment-skip use (those consume external inputs).
+
+The clear header (`<0x80`) is never scrambled, so its periodic crib predicts
+the plaintext at `0x80`. Descramble with the cached key; if the crib fails to
+reappear the key region changed (or the primed key was wrong) — restore the
+ciphertext, re-crack from this very sector, and descramble again. A crib-less
+sector (no periodic run) can be neither validated nor cracked, so it rides
+the cached key — correct, because it lives in the same region as the nearby
+crib sector that set the cache.
+
+This section used to document an `Error::DecryptFailed` for the case where a
+sector's crib rejects the cached key and the re-crack from that sector also
+fails. That behaviour was tried and REVERTED: crib mismatch plus crack
+failure is the signature of a crib FALSE POSITIVE, not of a stale key, and
+failing there made real discs unrippable. The code now descrambles with the
+cached key and returns `Ok`.
+
+## `has_scramble_flag_bits`
+
+Deliberately NOT called `is_scrambled`. Byte 0x14 only means "scrambling
+control" inside an MPEG-2 Program Stream pack; in an IFO, UDF or ISO 9660
+sector it is whatever that format stores there. Treating the flag alone as
+proof of scrambling is what destroyed 1912 bytes of a real disc's
+`VIDEO_TS.IFO` — the sector carrying TT_SRPT — so the disc enumerated 38
+titles and an image decrypted from it enumerated 10, silently, at exit 0.
+
+Callers want `is_scrambled_pack`. It asks the same question and also
+requires the pack start code, which every genuinely scrambled VOB sector
+carries and no IFO sector does.
+
+It stays public only because an integration test asserts the flag
+extraction directly. It has no production callers, and its previous doc
+comment claimed one (`decrypt::decrypt_sectors`) that did not exist — so the
+name was an invitation and the documentation was an argument for accepting
+it.
+
+## `is_scrambled_pack`
+
+The HARDENED test the crack scan uses to set its `saw_scrambled` evidence
+flag (Fix 3).
+
+`has_scramble_flag_bits` keys solely on bits 4-5 of byte 0x14. That byte is
+only meaningful inside a real DVD sector — an MPEG-2 Program Stream pack,
+which ALWAYS begins with the 32-bit pack-start code `00 00 01 BA` at offset
+0x00. A tiny clear / nav-only stub (a 0.5 s menu loop, an FBI-warning title)
+can carry arbitrary bytes that happen to set bits 4-5 of byte 0x14; trusting
+byte 0x14 alone there would flip the scan's `saw_scrambled` gate and make a
+genuinely-UNENCRYPTED title report `ScrambledUncracked` — a false E7023.
+
+Requiring the pack-start signature FIRST means only a sector that is
+structurally a DVD video pack can be counted as scramble evidence. This does
+NOT weaken the genuine "encrypted but uncrackable" hard-fail: a real
+scrambled feature is made of valid PS packs, so its scrambled sectors still
+pass this check and still drive `ScrambledUncracked` when no key cracks.
+
+The pack-start check alone is not enough, and the sector's PES `stream_id`
+(offset 0x11, the byte after the 14-byte pack header's `00 00 01` PES
+prefix) is the second load-bearing gate. CSS scrambles ONLY elementary
+streams — video (`0xE0..=0xEF`) and private_stream_1 audio/subpicture
+(`0xBD`) — and it never touches the clear header, so byte 0x11 is the TRUE
+stream_id even on a scrambled sector. The MPEG-PS structural packets that
+are never CSS-scrambled — system_header (`0xBB`), padding (`0xBE`) and
+private_stream_2 (`0xBF`, DVD PCI/DSI navigation) — must be excluded,
+because on those the byte at 0x14 is NOT a PES scrambling-control field but
+raw payload/structure whose bits 4-5 land set by chance.
+
+This is the DETECTION defect a decrypted HD-DVD tripped: an HD-DVD `.evo` is
+MPEG-PS exactly like a DVD `.vob`, and its RDI navigation packs are
+private_stream_2 (`0xBF`) whose payload byte at 0x14 routinely has bits 4-5
+set. With no `0x11` gate those nav packs flipped the crack scan's
+`saw_scrambled` flag on a disc that carries no CSS at all; the crack then
+found no key (there is none) and the scan returned `ScrambledUncracked`,
+hard-failing a perfectly good HD-DVD with `CssKeyMissing` — E7023. Excluding
+`0xBB/0xBE/0xBF` at 0x11 makes the evidence gate match what the crack itself
+can act on (the recovery only recovers a key from a scrambled ES pack), so a
+decrypted HD-DVD now scans to `Unencrypted` and muxes cleanly.
+
+This does NOT weaken the genuine "encrypted but uncrackable" hard-fail on a
+real DVD: a scrambled DVD feature is made of video (`0xE0..`) and
+private_stream_1 (`0xBD`) packs, none of which are excluded, so its
+scrambled sectors still set `saw_scrambled` and still drive
+`ScrambledUncracked` when no key cracks. Byte 0x11 is in the clear header,
+so a scrambled DVD pack can never masquerade as `0xBB/0xBE/0xBF`.
+
+The DESCRAMBLE path gates on this same function — `descramble_sector` and
+`descramble_region` both call it, not the raw flag test — because the raw
+test does not merely mis-skip a sector there: it descrambles one that was
+never scrambled and destroys it. The measured case is written up above under
+`descramble_region`: a `VIDEO_TS.IFO` sector holding 0x15 at offset 0x14 lost
+1912 of its 2048 bytes, taking TT_SRPT with it, and the disc's 38 titles
+became 10 — silently, at exit 0. One gate, both paths.
+
+## Tests (`mod tests`)
+
+Detail relocated from test doc comments:
+
+- `a_crib_false_positive_keeps_the_cached_key_rather_than_failing`:
+  `attack_crib` is a heuristic — it finds a periodic run in the unscrambled
+  header and predicts the run continues past 0x80. When that prediction does
+  not hold, the crib reports a mismatch even though the cached key is
+  correct, and the re-crack then fails BECAUSE the crib was never valid. So
+  this combination is the signature of a crib false positive, not of a stale
+  key, and the cached key remains the best available evidence. This test
+  exists because a prior round read the same code as "descrambling with a
+  key we just proved stale" and made it `DecryptFailed` to match the AACS
+  path; real DVDs hit this constantly, and the change made a real disc
+  unrippable (no unit test caught it — the real-media acceptance gate did).
+  CSS is not AACS: an AACS unit key either opens a unit or does not, whereas
+  a CSS title key is recovered from data whose recoverability varies sector
+  by sector.
+
+- `has_scramble_flag_bits_short_buffer_is_false_no_panic`: grounding —
+  `sector.len() >= 2048 && (sector[0x14] >> 4) & 0x03 != 0` short-circuits so
+  a short buffer never reads index 0x14. Mutation: swapping operand order
+  would panic indexing a 20-byte slice; this test catches it.
+
+- `has_scramble_flag_bits_uses_bits_4_5_only`: grounding —
+  `(sector[0x14] >> 4) & 0x03`. Mutation: widening the mask to `& 0x0F` makes
+  0x40 report scrambled; the 0x40 assert catches it.
+
+- `has_scramble_flag_bits_exact_sector_length_accepted`: grounding —
+  `sector.len() >= 2048`. Mutation: `>= 2048` → `> 2048` makes an exact
+  2048-byte scrambled sector report false; this catches it.
+
+- `is_scrambled_pack_requires_pack_start_signature`: Fix 3 hardening —
+  `is_scrambled_pack` requires BOTH the pack-start code and the 0x14 bits, so
+  a clear/nav-only stub with stray 0x14 bits isn't scramble evidence (else a
+  genuinely unencrypted title reports the false E7023).
+
+- `is_scrambled_pack_excludes_nav_and_structural_stream_ids`: detection fix —
+  `is_scrambled_pack` must exclude system_header/padding/private_stream_2 by
+  `stream_id` at 0x11, since CSS never scrambles those and byte 0x14 there is
+  raw payload, not a scrambling-control field. This is the exact
+  decrypted-HD-DVD defect (an `.evo` RDI pack is 0xBF with pack-start and
+  0x14 bits set); the video/private_stream_1 cases prove the exclusion
+  doesn't weaken real-DVD detection.
+
+- `MockSource` fields `lock_all`, `crackable`, `short_read`, `stream_id`: model
+  a CSS-locked drive (`05/6F/03` on every read), a designated crackable LBA
+  serving a full synthetic scrambled sector, a short-read count (the
+  `recovery: true` short-read contract, `Some(0)` being the degenerate
+  spin-guard case), and the PES `stream_id` written at 0x11 (used to model an
+  HD-DVD `.evo` RDI nav pack via `PRIVATE_STREAM_2`).
+
+- `crackable_sector`: builds a crackable scrambled sector whose cleartext
+  header (0x59..0x80) carries a periodic run continuing across the 0x80
+  boundary, mirroring the `synth_periodic_sector` fixture in the keyless
+  tests but built from the crate-internal `scramble_sector`.
+
+- `a_source_that_returns_zero_sectors_still_obeys_the_scan_budget`: `tried`
+  increments only per inspected sector inside `for s in 0..usable`; an
+  `Ok(0)` never runs that loop, so `advance` is forced to 1 to keep the
+  cursor moving and the extent's full declared length is walked. Mutation:
+  deleting the `tried` charge in the `usable == 0` arm goes red at 60,000
+  reads for a misbehaving/adversarial source.
+
+- `crack_key_caps_total_tries_at_50000`: grounding — `max_tries = 50_000`,
+  `tried += 1` before the read, loop guard `tried < max_tries`. Mutation:
+  widening the cap, or removing the increment, both go red.
+
+- `crack_key_budget_is_shared_across_extents`: grounding — `tried` is
+  declared outside the extent loop with a shared `if tried >= max_tries`
+  break. Mutation: moving the declaration inside the loop would give each
+  extent its own budget (80,000 total instead of 50,000).
+
+- `crack_key_scans_from_extent_start_lba`: grounding —
+  `reader.read_sectors(ext.start_lba + i, ...)`. Mutation: dropping
+  `ext.start_lba +` would start LBAs at 0 instead of the extent's start.
+
+- `crack_key_continues_past_read_errors`: grounding — a read `Err` falls
+  through to the next sector rather than aborting. Mutation: propagating the
+  error with `?` would stop the scan after the first failure.
+
+- `crack_key_empty_extent_reads_nothing` / `crack_key_no_extents_is_none`:
+  grounding — `while i < ext.sector_count` / `for ext in extents` are no-ops
+  on empty input; an off-by-one (`<=`) or a pre-loop read would break these.
+
+- `crack_outcome_reaches_cracked_with_span`: audit gap "MockSource never
+  yields a crackable sector" — drives the full `crack_key_scan` over a
+  synthetic ISO to exercise the `Cracked` branch and `crack_span` recording
+  end-to-end, previously untested.
+
+- `is_scrambled_uncracked_is_true_for_that_case_and_false_for_the_other_two`:
+  a prior round introduced the three-way split precisely because conflating
+  the cases made an uncrackable disc exit 0 with garbage output; earlier
+  tests only asserted the TRUE direction, so a predicate answering "yes"
+  unconditionally was indistinguishable from a correct one. All three
+  outcomes here come from real `crack_key_outcome` scans, not hand-built enum
+  values.
+
+- `resolve_dvd_title_key_*` tests: `resolve_dvd_title_key` is the SINGLE
+  shared per-title CSS step both read paths (`build_iso_pipeline` multi-pass
+  and `DiscStream::new` single-pass) call, so these pin its full contract at
+  the shared boundary — crack success, hard-fail on scrambled-uncrackable
+  (never leaving `keys` as `None`, which would mux scrambled bytes as
+  plaintext), the decrypted-HD-DVD RDI-pack regression (end to end), `--raw`
+  passthrough, the AACS-keys-untouched gate, the clear-DVD no-op, and the
+  halt-cancellation-surfaces-as-Halted fix (not a truncated-scan verdict).
+
+- `all_locked_synthetic_iso_yields_css_key_missing_signal`: audit §2/§5 #7 —
+  pins that an all-locked synthetic ISO across MULTIPLE extents produces
+  `ScrambledUncracked`, the exact signal `disc/mod.rs` converts into
+  `disc.css_error = Some(Error::CssKeyMissing)`.
+
+- `recrack_succeeds_on_other_vts_extents`: audit gap "success path missing"
+  — the prior re-crack test only covered the locked→None path; this proves a
+  key cracked for one VTS is genuinely re-derived (not reused) for another.

docs/ctrm.md

@@ -0,0 +1,32 @@
+# Warner CTRM label parser — relocated rationale
+
+Referenced from `src/labels/ctrm.rs` unit tests via `// See docs/ctrm.md` pointers.
+
+## Immunity pin: no analog of the `paramount` forced_sub false positive
+
+Immunity pin against the defect measured in the `paramount` parser, where a
+vendor `forced_sub` cell hung off a FULL dialogue track's own slot to say
+"this track also contains forced signs", and reading that cell as "this
+track is forced" flagged 30 MB dialogue tracks forced.
+
+This format cannot express that. The forced signal is not a flag beside a
+track's entry — it IS the entry's stream-kind token, drawn from a closed
+vocabulary in which `subtitle_production` (the full dialogue track) and
+`subtitle_narrative` (the forced-narrative track) are mutually exclusive
+alternatives in the same position. A row is one or the other; there is no
+cell a full track can carry to acquire the qualifier, so the paramount
+failure mode has no encoding here.
+
+Mutation: give `subtitle_production` a `Forced` qualifier, or add a forced
+side-flag that both kinds may carry.
+
+## Immunity pin: stream numbers come from the row, not a counter
+
+`language_streams.txt` states each stream's number in field 3, so a row the
+parser cannot use is simply dropped — it can never renumber the rows behind
+it. This is the property that keeps this parser out of the STN-slot-shifting
+failure mode that bites parsers which count positionally: there, a skipped
+entry silently pulls every later label one stream forward.
+
+Mutation: replace `parts[2]` with a running per-type counter → the three
+unusable rows in the corresponding test collapse the survivors onto 1/2 and 1.

docs/dbp.md

@@ -0,0 +1,39 @@
+# `labels::dbp`
+
+## Implementation
+
+Iterates `CpInfo::Utf8` constant-pool entries rather than raw
+byte-scanning each class file. Equivalent label coverage (the literal
+`TextField,...` strings live in the CP as Utf8 entries) with no
+false-positive risk from method bytecode or attribute names that
+happen to contain `TextField,`. Language / purpose / qualifier
+classification lives in `super::vocab` so all Java-parser families
+share one source of truth.
+
+The parser ignores any prefix before the first `TextField,` occurrence
+in a constant string — whatever string-pool ordering placed ahead of
+it is irrelevant.
+
+## `MAX_LABEL_BYTES` rationale
+
+The label is an owned copy of a slice of a `CONSTANT_Utf8_info` entry,
+whose `length` field is a `u16` (JVMS §4.4.7) — so a single crafted
+constant contributes up to 65535 bytes, and the `u16` stream-number
+keyspace admits 65536 of them per type.
+
+Headroom: real dbp menu labels are short display names — "English Dolby
+Atmos" (19 bytes), "Spanish 5.1 Dolby Digital" (25). The longest plausible
+retail string ("Portuguese (Brazilian) 5.1 Dolby Digital Plus") is 45
+bytes. 256 leaves >5x headroom over that, and any string past it is menu
+geometry or padding, never a language name — `vocab::lang` would not
+resolve it anyway.
+
+## `MAX_LABELS_PER_TYPE` rationale
+
+The keys come from `parse::<u16>()` on disc bytes, so all 65536 slots per
+type are reachable; paired with `MAX_LABEL_BYTES` this bounds the whole
+scan at 2 x 512 x 256 bytes.
+
+Headroom: the BD STN_table admits at most 32 primary audio and 32 PG
+streams per playlist, and dbp emits one menu TextField per stream. 512
+leaves 16x headroom over the spec maximum.

docs/decrypt.md

@@ -0,0 +1,500 @@
+# decrypt.rs — relocated rationale
+
+Overflow prose that would not fit under `ci/comment-guard.py`'s caps,
+moved here per file with a `// See docs/decrypt.md — <topic>` pointer
+left at the original site.
+
+## Parallel AACS decrypt
+
+Each AACS aligned unit (6144 bytes) is decrypted INDEPENDENTLY of every
+other unit — per-unit key derivation from the unit_key plus the unit's
+own first-16-byte header. There is no cross-unit dependency, so a
+buffer of N units can be decrypted on N threads in parallel via a
+persistent rayon thread pool.
+
+Small buffers (< `PARALLEL_MIN_UNITS` units) fall through to the serial
+path to avoid pool dispatch overhead beating the per-unit AES work.
+
+## Thread-count configuration — three layers
+
+Resolution order (highest wins):
+1. The most recent `set_decrypt_threads` call with `n > 0`. Calling
+   this *replaces* the live thread pool — useful for a settings-page
+   slider in a long-running daemon.
+2. `FREEMKV_THREADS` env var, if set and `> 0`. Single knob covering
+   decrypt today, intended to also drive any future input-side /
+   output-side worker pools.
+3. Default: all available cores. Algorithm optimisation comes first —
+   we measure single-thread performance to find serial bottlenecks
+   before throwing parallelism at it — but once a pool is engaged we
+   use the whole box. Hard cap at `MAX_THREADS` (rayon stack memory).
+
+## DECRYPT_POOL
+
+Current rayon pool. `RwLock<Option<Arc<...>>>` so that
+`set_decrypt_threads` can swap the pool out without leaking the old
+one and without blocking ongoing decrypt work (in-flight calls hold an
+`Arc` clone via `decrypt_pool` and finish on the old pool; new calls
+pick up the new pool).
+
+## decrypt_pool()
+
+Get (or lazily build) the active rayon thread pool. Returns an `Arc`
+so in-flight work survives a concurrent `set_decrypt_threads` swap.
+
+Returns `None` if the pool cannot be built (e.g. the OS refuses the
+worker threads under a pid/thread limit). The caller falls back to the
+serial decrypt path — library code never panics here.
+
+## unit_is_our_phase
+
+Does this unit belong to the phase we hold the key for?
+
+An FMTS forensic segment interleaves two variants at the unit level:
+the disc carries both, and we hold the key for exactly one parity.
+Decrypting the alternate half with our key produces garbage; leaving
+it as ciphertext is correct, because the muxer drops untouched
+ciphertext cleanly.
+
+`Phase::All` means the whole range is ours (the non-forensic case).
+
+This lived inline inside `apply_aacs_map`'s per-unit closure, where
+nothing could reach it: a mutation run flipped the `-` to `+` and the
+`/` to `*` in the index arithmetic and every test still passed.
+Getting either wrong silently decrypts the wrong half of a forensic
+segment.
+
+## AacsKeyMap (proactive AACS key-selection map)
+
+Which held unit key decrypts each LBA of a title's encrypted content,
+decided ONCE before mux from the disc's CPS-unit (and, later, FMTS
+segment) structure — never by trial-decrypt-and-check per unit at mux
+time.
+
+This is the pivot that ends the mux "key-server storm": the old path
+decrypts a unit, checks whether the plaintext looks like clean MPEG-TS,
+and — because authored-bad content never reaches that bar — concludes
+"wrong key, fetch a fresh one" and re-asks the key service for units it
+already holds the correct key for. There is NO per-unit byte pattern
+that separates "correctly decrypted but authored-bad" from "still
+encrypted", so that check is unanswerable. The map removes the
+question: we resolve one key per CPS unit / segment up front (see
+`resolve_mux_key_map`), record which LBA ranges each covers, and at mux
+time simply "decrypt this LBA with key K" and trust it — bad TS is the
+muxer's concern, exactly as for a physically-read clear disc.
+
+Ranges are `[start_lba, end_lba)` → index into the `Aacs { unit_keys }`
+pool, sorted and disjoint. The map is a POSITIVE list: an LBA in no
+range is passed through untouched (no default key). How a single-CPS
+disc is mapped depends on the caller: the whole-disc EXTRACT path uses
+one blanket range `(0, u32::MAX, 0)` so every encrypted unit — parsed
+title or orphan clip — resolves to key 0; the per-title MUX/sweep path
+(`resolve_mux_key_map` → `content_map`) maps only the title's own
+extents, so an orphan clip outside them is left as pass-through. Either
+way, clear nav/filesystem sectors (encrypted-flag off) pass through.
+
+## AacsKeyMap::read_plan
+
+Build the FMTS **read plan**: the title's aligned units filtered down
+to only the units this rip must actually read — every default / CPS
+unit, plus, inside each forensic segment, ONLY our-phase (`Phase::Even`
+/ `Phase::Odd`) units. The alternate-phase units are a different device
+group's variant: a licensed player never reads them, and neither do we.
+They are omitted from the plan entirely, so they are never fetched,
+decrypted, or handed to the demux — the demux therefore sees one
+gapless our-variant stream, with no ciphertext to trip a
+concealed-gap resync (the old behaviour that dropped good frames
+around every segment).
+
+`extents` are the title's clip extents (unit-aligned in the interior; a
+shorter tail is ordinary content and always kept). `unit_sectors` is
+the AACS aligned-unit size in sectors (3). Contiguous kept units
+coalesce into as few extents as possible so the producer still issues
+large sequential reads across default content; only inside a ~480 KB
+forensic segment do reads become unit-granular (every other unit). A
+map with no forensic (Even/Odd) range returns `extents` unchanged — the
+common disc is not touched.
+
+The parity test is byte-identical to the decrypt hot loop
+(`(unit_lba - range_start) / unit_sectors`), so a unit kept here is
+exactly a unit `decrypt_sectors_mapped` would open, and vice-versa.
+
+## apply_aacs_map
+
+AACS scheme step: apply `map`'s per-unit keys to `buf`, in-place.
+`base_lba` is the absolute LBA of `buf`'s first sector; each aligned
+unit (3 sectors) is decrypted with the key the map assigns to its LBA.
+There is NO key trial and NO `is_clean` verdict: the map already
+decided the key from disc structure, so this applies it and moves on —
+a unit that decrypts to authored-bad TS passes through for the muxer to
+drop, never re-fetched.
+
+A SCHEME, not a policy. It reports what it could not open by returning
+`Err(DecryptFailed)`; the decision that an unopenable unit must never
+be emitted belongs to `decrypt_span`, which is the one place that
+decides it for every scheme. A map index outside the held pool is
+likewise a fail-loud `Error::DecryptFailed`: the resolver's job is to
+guarantee every selectable index is present, so a gap here is a
+resolver bug, not silent loss.
+
+## decrypt_sectors — CSS / clear detail
+
+For CSS: descrambles per 2048-byte sector, self-cracking the title key
+from the data (no external input). For `None`: a no-op. For AACS:
+**always** returns `Err(DecryptFailed)` — AACS decrypts exclusively
+through the resolved key map (`decrypt_sectors_mapped`), which keys
+every content unit up front and fails at RESOLVE time when a key is
+missing. Reaching this arm with AACS keys means a reader was built
+without installing its map (a bug), so it fails loud rather than apply
+a guessed key.
+
+`unit_key_idx` is a legacy parameter kept so the CSS / `None` wrapper
+signature stays stable; it is ignored (the CSS arm self-gates on its
+per-sector scramble flag). Returns `Err` if decryption was expected but
+impossible; never produces silently corrupted output. The `usize`
+return is a legacy unverified-byte count that is always `0` for the CSS
+/ `None` arms.
+
+## decrypt_span — orchestrator rationale
+
+THE decrypt orchestrator. Every path into this crate's decryption goes
+through here.
+
+How a disc decrypts is one process — resolve a key for this span,
+apply it, and refuse if no key can be proven. Only the resolve-and-apply
+step is scheme-specific. This function owns the loop and the refusal;
+the schemes below supply only what genuinely differs between AACS, CSS
+and clear media.
+
+That split exists because its absence caused six separate defects in
+one release. There used to be TWO top-level paths — this one for CSS
+and clear, and a wholly separate `decrypt_sectors_mapped` for AACS
+whose arm here was a bare `return Err` stub — so each scheme decided
+its own answer to "there is no key for these bytes" and nothing held
+them to the same one. CSS drifted to descrambling with a key it had
+just proven stale; the mapped path drifted to passing an unkeyable
+encrypted unit through as ciphertext. Both looked like success to the
+caller.
+
+Adding a scheme means adding an arm here, which means answering the
+refusal question. That is the point.
+
+## Tests — relocated rationale
+
+### a_forensic_read_plan_drops_units_the_full_extents_include
+
+`DecryptKeys::None` is a no-op even with a content map + scrambled
+bytes. A forensic map's read plan is NOT the extents it was given —
+and that is the precondition the mux's provenance guard keys on.
+
+A clip's feed span is measured over the FULL extents at scan time,
+while the mux reads this reduced plan, so the byte offsets stamped on
+frames and the offsets recorded in the spans describe different
+streams. The deficit accumulates, so every frame after the first
+segment resolves to an earlier clip than it came from. The spans still
+tile each other, so the tiling check cannot see it; the mux compares
+the plan against the full extents instead and stops trusting
+provenance when they differ.
+
+### content_gate_css_keys_is_noop
+
+CSS ignores the content gate (it lives in the AACS arm) and always
+reports `0` — confirming the gate is a no-op for CSS and the read
+stays scheme-agnostic (the litmus test: adding CSS verify touches only
+the CSS arm, never the read).
+
+### content_gate_css_actually_descrambles_the_buffer
+
+`decrypt_sectors_in_content` is the entry point `DecryptingSectorSource`
+dispatches to whenever a content map is installed
+(`sector/decrypting.rs` line ~211), so it is on the live read path for
+every mapped rip. It must actually DECRYPT. The two `_is_noop` tests
+above only assert its `usize` return is `0` — which is what a body
+replaced by `Ok(0)` also returns, so neither one constrains it at all.
+
+Here a genuinely scrambled CSS sector goes in and the CONSTRUCTED
+plaintext must come out. Anything that skips `css::descramble_region` —
+including a body that just reports `Ok(0)` — leaves ciphertext in the
+buffer and the caller muxes scrambled MPEG at exit 0.
+
+Expected bytes come from the plaintext this test built BEFORE
+scrambling (CSS scrambles only 0x80..2048; the header stays clear), not
+from re-running any descramble routine.
+
+### content_gate_aacs_keys_fail_loud_not_ok_zero
+
+The AACS arm of the same entry point must fail LOUD. Under the
+keymap-only model AACS decrypts exclusively through
+`decrypt_sectors_mapped`; reaching this wrapper with AACS keys means a
+reader was built without installing its key map, and continuing would
+hand the caller ciphertext under an `Ok`. `DecryptFailed` is the
+correct verdict per the function's own contract — it must not be
+softened into a success with a zero count.
+
+### css_region_change_recracks_the_title_key
+
+CHARACTERIZATION (recovery refactor safety net): the CSS arm's
+per-region re-crack (the `title_key` cache is stale for a new VOB
+region → restore ciphertext, `crack_title_key` this sector,
+re-descramble). Two crackable sectors scrambled under DIFFERENT keys
+sit back-to-back; the cache is primed to the FIRST key. Sector 0 rides
+the cache (crib matches); sector 1 must trip the crib mismatch and
+re-crack to its own key. Both must land correct plaintext, and the
+cache must end on region 1's key.
+
+This behaviour currently lives inline in `decrypt_sectors` (the `Css`
+arm). It is the delicate logic the recovery refactor will move to the
+input-stream seam, so it must stay green byte-for-byte across that
+move.
+
+### aacs_scrambled_trailing_partial_is_rejected
+
+Whole leading unit plus a SCRAMBLED trailing partial that is FLAGGED
+encrypted in its clear seed (the malformed danger case): an encrypted
+unit split across an extent boundary cannot be CBC-decrypted
+standalone. The mapped decrypt must fail loud with `DecryptFailed`
+rather than emit the ciphertext partial as clear. Exercises the real
+shipping path (`decrypt_sectors_mapped`) and its trailing-partial
+guard.
+
+### aacs_clear_trailing_partial_passes_through
+
+A CLEAR trailing partial (encrypted flag NOT set) is a legitimate
+content tail and must pass through, never trip the guard above.
+
+"Passes through" means byte-for-byte unchanged, not merely `Ok`.
+Asserting only `is_ok()` let a mutant that corrupts the clear partial
+while still returning `Ok` pass — which is the whole failure this test
+names. Mutation: XOR any byte of the tail before returning -> the
+snapshot comparison fails.
+
+### none_keys_is_noop
+
+`DecryptKeys::None` is a pure no-op: the buffer must be returned
+byte-for-byte unchanged with Ok, regardless of content (even content
+that looks scrambled).
+
+Grounding: the `DecryptKeys::None => {}` match arm does nothing.
+Mutation: replace the empty arm with a call that mutates buf -> the
+unchanged assert fails.
+
+### is_encrypted_matches_variant
+
+`is_encrypted` reflects the variant: None -> false, Css/Aacs -> true.
+
+Grounding: `!matches!(self, DecryptKeys::None)`.
+Mutation: invert the `!` -> None reports true, this fails.
+
+### css_descrambles_with_title_key
+
+The CSS path descrambles each 2048-byte sector with the title key. A
+scrambled sector run through decrypt_sectors must come back to its
+plaintext body (keystream XOR is involutive), proving the title key is
+actually applied.
+
+Grounding: `DecryptKeys::Css { title_key } => for chunk in
+buf.chunks_mut(2048) { descramble_sector(title_key, chunk) }`.
+Mutation: change `chunks_mut(2048)` to `chunks_mut(2049)` or pass a
+fixed wrong key -> the body no longer matches the plaintext.
+
+### css_processes_every_sector_in_buffer
+
+The CSS path processes EACH 2048-byte sector independently in a
+multi-sector buffer. Two scrambled sectors (with different seeds) in
+one buffer must both round-trip — pinning that the loop steps by 2048
+and applies the key to every sector, not just the first.
+
+Grounding: `for chunk in buf.chunks_mut(2048)`.
+Mutation: change the loop to descramble only the first chunk (e.g.
+`.next()`) -> the second sector stays scrambled, assert fails.
+
+### css_rekeys_when_title_key_region_changes
+
+CSS title keys are per-VTS/VOB region: a real disc holds DIFFERENT keys
+for different regions and the only way to get each is to crack it. The
+decrypt path must re-crack when the cached key stops descrambling (its
+crib no longer reappears at 0x80) instead of blindly applying one key
+across a region boundary — the bug that pixelated every freemkv DVD
+rip.
+
+Two sectors scrambled under DIFFERENT keys, cache primed to ONLY the
+first (exactly what the one-shot scan crack leaves). Sector 0 validates
++ descrambles with the cached key; sector 1's cached-key descramble
+fails the crib, so the path re-cracks sector 1's own key and recovers
+its plaintext. Before the fix (blind single-key apply) sector 1 was
+garbage.
+
+Grounding: the CSS arm's `attack_crib` → `chunk[0x80..] != crib` →
+`crack_title_key` → `*title_key = fresh` rekey.
+Mutation: drop the rekey branch (apply the cached key always) →
+sector 1's body no longer matches its plaintext; this fails.
+
+### css_leaves_clear_sector_unchanged
+
+The CSS path leaves UNSCRAMBLED sectors (flag clear) byte-for-byte
+untouched — descramble_sector early-returns on a zero flag. A clear
+sector mixed into the buffer must not be corrupted.
+
+Grounding: descramble_sector returns immediately when
+`(sector[0x14] >> 4) & 0x03 == 0`.
+Mutation: remove that early return in lfsr.rs -> a clear sector would
+be XORed with a keystream and change; this fails.
+
+### css_empty_buffer_is_ok
+
+CSS decrypt always returns Ok (it cannot fail — descrambling is XOR,
+no key validity check), even for an empty buffer.
+
+Grounding: the CSS arm has no `return Err` path; `chunks_mut` over an
+empty slice is a no-op; the function ends `Ok(())`.
+Mutation: make the CSS arm return Err -> this fails.
+
+### aacs_mapped_out_of_range_key_idx_errors
+
+A map that selects a key index OUTSIDE the held pool must fail loud
+with DecryptFailed — never silently apply a wrong key or pass
+ciphertext through. This validates `decrypt_sectors_mapped`'s up-front
+`key_indices()` bounds check (the real shipping AACS decrypt path).
+
+Mutation: drop the `unit_keys.get(idx).is_none()` guard → the
+out-of-range index would not error; this fails.
+
+### aacs_via_unmapped_decrypt_sectors_fails_loud
+
+SAFETY NET: reaching the CSS/`None` wrapper (`decrypt_sectors`) with
+AACS keys means a reader was built with no map — a bug. It must fail
+loud, never apply a guessed key. (AACS decrypts exclusively via
+`decrypt_sectors_mapped`.)
+
+### read_plan_forensic_reads_only_our_phase_units
+
+FMTS: a forensic Even segment drops exactly its alternate (odd) units
+from the read plan — they are never fetched — while default content on
+either side stays one coalesced sequential run. The kept units are
+byte-identical to the ones the decrypt hot loop opens.
+
+### read_plan_phase_parity_is_measured_from_an_unaligned_range_start
+
+A forensic range does NOT start on an aligned-unit boundary. Its start
+LBA comes from a source-packet number — `start_spn * 192` put through
+`clip_byte_to_lba` (`mux/resolve.rs`) — and 192-byte packets have no
+relationship to the 3-sector aligned unit, so `range_start % 3` is
+whatever the disc says.
+
+That makes `unit_ix = (lba - range_start) / us` load-bearing in both of
+its operations, and the existing coverage used a range starting exactly
+on the extent's first unit, where several wrong formulas agree with the
+right one by arithmetic accident.
+
+Getting the parity wrong is not a crash. It reads and decrypts the
+ALTERNATE variant's half of a forensic segment: the units this disc's
+key does not open decrypt to garbage, and the units it does open are
+skipped. AACS 2.1 forensic marking is exactly the mechanism that makes
+the two halves different, so a phase inversion is silent — it produces
+a full-length rip carrying the wrong variant.
+
+### read_plan_gates_the_last_whole_unit_of_an_extent_not_just_the_remnant
+
+An extent whose last whole unit is an alternate-phase unit must still
+drop it. The tail guard exists for a REMNANT shorter than a unit —
+bytes with no following unit to desync — and an extent ending exactly
+on a unit boundary has no remnant at all.
+
+With the guard widened to `remaining <= us`, the final unit of every
+extent bypasses the phase gate and is read unconditionally. On a
+forensic segment that lands at an extent end, that is one
+alternate-variant unit pulled into the rip and decrypted with a key
+that does not open it.
+
+### every_scheme_gives_the_same_verdict_when_no_key_can_be_proven
+
+Every scheme that CANNOT prove a key answers the same way.
+
+This is the property `decrypt_span` exists to hold. There used to be
+two top-level decrypt paths — one for CSS and clear media, one for
+AACS — and each decided its own answer, so they drifted apart in
+opposite directions within a single release: CSS descrambled with a
+key it had just proven stale, and the AACS path passed an unkeyable
+encrypted unit through as ciphertext. Both reported success.
+
+Asserting one verdict across the schemes is what makes a future
+divergence a test failure rather than a silent corruption. A
+per-scheme test cannot do that: each would still pass while the two
+disagreed.
+
+CSS is deliberately NOT in this list. Its title key is recovered from
+the data, sector by sector, by a heuristic that false-positives — a
+crib mismatch whose re-crack fails means the crib was wrong, not that
+the key is stale, so the cached key is kept and used. Round 9 folded
+CSS in here on the reasoning that "no key" should mean one thing
+everywhere; that made real DVDs unrippable, and the real-media gate
+caught it. Uniform policy is right for schemes that can PROVE a key
+wrong. CSS cannot.
+
+### an_encrypted_unit_outside_every_key_range_fails_instead_of_passing_through
+
+An ENCRYPTED unit that falls outside every key-map range must fail,
+not pass through as ciphertext.
+
+"The map has no key here" and "there is nothing to decrypt here" are
+different statements, and only the second makes passing the unit
+through correct. On a multi-CPS disc an orphan clip — referenced by no
+playlist, so in no title extent and therefore in no range — hits the
+first and was treated as the second. `extract_tree` then counted those
+bytes as GOOD, dropped the `.partial` suffix, and reported `complete:
+true`, exit 0: a scrambled file on disk with a clean bill of health.
+
+A CLEAR unit outside every range is the ordinary case (filesystem and
+nav on a whole-disc read) and must still pass through untouched — so
+this asserts both directions.
+
+### mapped_key_selection_is_positional_so_pool_order_matters
+
+The mapped descramble indexes the committed key pool POSITIONALLY
+(`unit_keys[key_idx].1`), so the ORDER of the `Vec<UnitKey>` a
+`KeySource` returns is load-bearing — it is NOT "cosmetic, the decrypt
+path strips it and tries every key", as
+`keysource::resolve_and_apply_traced`'s doc used to claim. Trial-decrypt
+was deliberately deleted; nothing here searches the pool. Reordering
+the same two keys therefore sends each range to the WRONG key: the
+range that decrypted clean now fails the correct-phase `is_clean` net
+loudly (or, off a forensic phase, would decrypt a whole span under a
+neighbour's key). Pins the corrected doc.
+
+### decrypt_threads_within_valid_pool_range
+
+The default (auto) decrypt thread count is always a usable pool size:
+at least 1 (a 0-thread rayon pool is invalid) and never above
+MAX_THREADS (rayon stack-memory cap). This test reads the resolved
+value without mutating the process-global override, so it is safe to
+run in parallel with other tests.
+
+Grounding: `cores.clamp(1, MAX_THREADS)` in the default branch;
+`env.min(MAX_THREADS)` in the env branch.
+Mutation: change `.clamp(1, MAX_THREADS)` to `.clamp(0, MAX_THREADS)`
+on a 0-core probe (unlikely) — more robustly, change the cap to
+`MAX_THREADS * 2` -> on a many-core CI box the upper-bound assert can
+fail. The lower-bound (>=1) guard is the load-bearing invariant.
+
+### phase_gate_selects_only_our_parity_of_a_forensic_segment
+
+The FMTS phase gate picks which half of an interleaved forensic
+segment we decrypt. Both the `-` and the `/` in its index arithmetic
+survived a mutation run, and getting either wrong silently decrypts the
+alternate variant into garbage while reporting success.
+
+### phase_gate_does_not_panic_on_a_malformed_map
+
+A malformed key map must not take down a long-running service. A unit
+below its own range start, or a zero unit size, are both map bugs —
+they must return a defined answer rather than panicking on debug
+overflow or dividing by zero.
+
+Every case here asserts the DEFINED answer, not merely the absence of a
+panic. The zero-unit-size case used to be written
+`assert!(unit_is_our_phase(100, 30, 0, Phase::Even) || true)`, which
+accepts both answers and so pinned nothing at all: the guards could
+invert and it would still pass. The answer is knowable —
+`saturating_sub` gives 70, `max(1)` makes the divisor 1, unit index 70
+is even — so pin it.
+</content>

docs/decrypting-sector-source.md

@@ -0,0 +1,34 @@
+# `DecryptingSectorSource`
+
+## Why this decorator is the single source of truth for decrypt-on-read
+
+Every decrypt-on-read caller (e.g. `DiscStream`) wraps its source in this
+decorator rather than calling the cipher helpers directly. The actual cipher
+code lives in `crate::aacs` and `crate::css`; the decorator just calls the
+existing `crate::decrypt::decrypt_sectors` helper that drives both of them
+in-place after each read. Centralizing the call site means callers can wire
+the decorator unconditionally and keep their pipeline shape uniform
+regardless of encryption state — for `DecryptKeys::None` discs it is simply
+a pass-through, so there is no branch in caller code for "is this disc
+encrypted?".
+
+## `KeyFetch`: why two explicit operations
+
+`KeyFetch` exposes `unit_keys` and `fmts_indexes` as two separate operations
+rather than one generic callback, so the "one base key vs. a whole forensic
+set" contract lives in the type instead of a caller guessing at the return
+length:
+
+* `unit_keys` resolves the base Unit Key(s) for a CPS unit from real
+  encrypted samples drawn from it. The non-forensic path: one key per CPS
+  unit (the pool grows by whatever it returns). Used by the mux's base /
+  multi-CPS map resolution and by the sweep/patch recovery decorator.
+* `fmts_indexes` resolves the disc's AACS 2.1 forensic index keys from an
+  index-1 single-phase anchor batch. The source hands back the COMPLETE set
+  (ordered index 1..N); the caller sizes the forensic map to `len()` and
+  never assumes a fixed N (32 is all we've seen, but the contract is
+  "whatever the source returns, >= 1, is all of them").
+
+`KeyFetch` is a stateless, shared pair of `Arc<Fn>`, so one instance is built
+once and cloned cheaply (two `Arc` bumps) into every read path; it is
+`Send + Sync` so it can ride the mux highway's producer thread.

docs/deluxe.md

@@ -0,0 +1,227 @@
+# Deluxe BD-J framework parser (`src/labels/deluxe.rs`)
+
+Detected on discs whose `/BDMV/JAR/<x>.jar` contains a `com/bydeluxe/`
+directory entry.
+
+## What this parser reads
+
+Deluxe-authored discs store stream labels as ordinal references into
+enum classes whose names are obfuscated per-disc, so a name-based
+match won't work. The label data is instead recovered by matching on
+the **shape of each enum's `<clinit>`**, which is framework-stable:
+
+| Enum | Signature |
+|---|---|
+| Language | 70 `ldc` operations in `<clinit>`, sequence starts `English, French, Spanish, Dutch, ...` |
+| Purpose | 8 ldcs starting `Normal, Commentary, PiP, Trivia, ...` |
+| VideoFormat | 7 ldcs starting `HD, HDR10 Plus, HD Dolby, ...` |
+| Region | 22 ldcs starting `USA_D1, LIC1, LIC2, LIC3, ...` |
+| Studio | 6 ldcs in `<clinit>` |
+
+Matching on the shape rather than the class name keeps the parser
+working across obfuscation variants. Codec strings come from the
+standard BD-J `org/bluray/ti/CodingType` enum referenced directly by
+the binding constructors (see `StackVal::CodingType`), not from a
+Deluxe-internal enum.
+
+## Implementation phases
+
+- **Phase A** — master enum identification (`identify_master_enums`).
+  Walks every `.class`'s `<clinit>` ldc sequence and matches against
+  the framework-stable fingerprints. Output: `Vec<(label, MasterEnum)>`
+  with full ordinal → string-value tables.
+
+- **Phase C** — binding-class identification (`find_binding_classes`).
+  The per-stream table is built by some class via repeated
+  `getstatic` references to the master enums identified in A.
+  That class has the highest such `getstatic` count in the jar.
+  Heuristic shape; precise threshold may need tuning.
+
+- **Phase D** — binding-class bytecode decoder (`decode_binding`).
+  Walks the binding class's `<clinit>` with a tiny symbolic stack
+  machine. For each `new X / dup / ... / invokespecial X.<init>`
+  sequence, collects the int values and enum-reference operands
+  between the `dup` and the constructor call, then emits a
+  `DecodedStream`. The signal-to-StreamLabel mapping (which arg is
+  stream index? which is language? audio vs subtitle?) uses a
+  heuristic — see `interpret_streams` for the mapping rules.
+
+## Confidence
+
+`parse` returns `Some(ParseResult::high(labels))` when Phases A
+through D produce at least one stream: the master enums matched their
+framework-stable fingerprints (a strong ordered-prefix signature), the
+binding class decoded, and at least one per-stream binding resolved to a
+real (language, purpose, codec) tuple — the schema was fully recovered,
+not guessed. `None` when the disc isn't Deluxe-authored or when decoding
+produces zero streams (a recognized-but-broken state that the analyzer
+still surfaces via `parsers_detected`).
+
+## Size caps (Phase A candidate pool)
+
+`MAX_CLINIT_LDC_STRINGS` (cap on `ldc` operands retained per class by
+`clinit_ldc_strings`): unlike every other count cap in this crate, the
+paired byte cap here cannot be the disc-file size — a `.class` entry
+gated only by a `com/bydeluxe/` path prefix deflates from ~100 KB up to
+the 64 MiB `MAX_CLASS_BYTES` read ceiling, so ~33M two-byte `ldc`
+instructions — one retained `String` each — are reachable from a small
+crafted disc. The bound has to be on the decompressed work, so it is
+applied here. Headroom: the largest framework-stable enum is `Language`
+at 70 values (`FINGERPRINTS`), and no fingerprint matches a count more
+than `LDC_COUNT_TOLERANCE` away from its expected size, so anything past
+~74 can never identify a master enum. 4096 leaves ~55x headroom over the
+largest real enum for framework drift.
+
+`MAX_CLINIT_LDC_BYTES` (companion byte cap): the count cap alone still
+admits 4096 x 64 KiB of `Utf8` (a JVMS `CONSTANT_Utf8_info` length is a
+u16), i.e. ~268 MB per class from repeated `ldc` of one huge constant.
+Headroom: master-enum values are short display names ("English",
+"HDR10 Plus", "USA_D1") well under 32 bytes, so a real Language enum
+retains ~1 KB. 256 KiB admits 4096 values averaging 64 bytes each.
+
+`MAX_CANDIDATE_TOTAL_BYTES` (aggregate companion, bounds retention across
+ALL classes at once): `identify_master_enums` holds every class's
+retained strings in one map simultaneously, so the per-class cap alone
+still admits `classes x 256 KiB`: a 64 MiB jar of minimal `.class`
+entries reaches tens of GiB. This is the same bound one level up.
+Headroom: the five `FINGERPRINTS` enums together hold ~113 short values
+(~1.2 KB). Every other class in a real BD-J jar contributes only
+whatever string constants its own `<clinit>` loads — resource paths,
+config keys — so a large authored jar lands in the low hundreds of KB.
+16 MiB leaves ~40x headroom over a deliberately generous 400 KB estimate
+for real media.
+
+`MAX_CANDIDATE_CLASSES` (entry-count companion to
+`MAX_CANDIDATE_TOTAL_BYTES`): the byte budget alone still admits ~16M
+map entries when every class retains a single one-byte `ldc`, and the
+per-entry `HashMap` + `String` overhead is not counted by that budget.
+Headroom: a large retail BD-J title ships on the order of 1-3k classes,
+and only those with a non-empty `<clinit>` ldc sequence become
+candidates. 65536 leaves >20x headroom over the class count of any real
+jar.
+
+## Internal helpers
+
+- `clinit_enum_field_names`: collects the static-field names an enum
+  class's `<clinit>` stores its own instances into, in declaration order
+  — the ordinal -> field-name mapping that mirrors `clinit_ldc_strings`'s
+  ordinal -> value mapping. An obfuscated Deluxe enum constant compiles
+  to `new E; dup; ldc "Value"; invokespecial E.<init>(…); putstatic
+  E.<field>`, so the `putstatic` whose owning class AND field descriptor
+  are both this class's own type names the field for that ordinal. The
+  binding class then references that constant as `getstatic E.<field>`;
+  without this mapping `MasterEnumTable` cannot turn the obfuscated field
+  name back into an ordinal. Bounded by `MAX_CLINIT_LDC_STRINGS` like the
+  value walk.
+
+- `clinit_ldc_strings`: walks `<clinit>` and collects every `ldc`/`ldc_w`
+  operand that resolves to a `String` or `Utf8` constant, in declaration
+  order; `None` if the class has no `<clinit>`. Collection stops at
+  `MAX_CLINIT_LDC_STRINGS` operands or `MAX_CLINIT_LDC_BYTES` of retained
+  text, whichever comes first: the walk is driven by the decompressed
+  class, so it isn't bounded by the disc-file size cap the way the rest
+  of this module's counts are. Truncation cannot lose a real match — a
+  truncated sequence is far longer than any `FINGERPRINTS` entry's
+  `expected_count + LDC_COUNT_TOLERANCE`, so it would have been rejected
+  on count anyway.
+
+- `find_binding_classes`: identifies all binding-class candidates by
+  getstatic-count to the master enums, using `MIN_GETSTATIC = 4` — the
+  binding class on a typical disc has 50+ such getstatic references (one
+  per slot x arity); the low floor lets a small disc with few streams
+  still qualify, while still filtering out classes that just reference
+  the language enum once for a config string. Some Deluxe discs split
+  the per-stream table across two binding classes (one for audio, one
+  for subtitle — the audio class commonly has the most getstatic refs,
+  the subtitle class somewhat fewer, both sharing the master Language +
+  Purpose enums), so this returns top-K candidates ordered by descending
+  getstatic count, filtered to a minimum concentration of references.
+
+`MAX_CONSTRUCTIONS` (Phase D, cap on `Construction`s retained from a
+binding `<clinit>` walk): one entry is appended per matched `new X / dup
+/ invokespecial X.<init>` with no other bound — a `.class` gated only by
+a `com/bydeluxe/` path prefix deflates to the 64 MiB `MAX_CLASS_BYTES`
+ceiling, and the shortest matching sequence is a handful of bytes, so
+millions of `Construction`s (each a `String` plus an arg `Vec`) are
+reachable from a small crafted disc (~1 GiB). The same cap bounds the
+per-class union in `decode_binding_class` (a crafted class may repeat
+`<clinit>`, which JVMS §4.6 forbids but this reader tolerates) and the
+cross-class union in `parse`, so the whole phase retains at most this
+many. Headroom: the BD `STN_table` (BDAV stream-entry counts) admits at
+most 32 primary audio and 32 PG streams per playlist, and a Deluxe
+binding table covers the disc's playlists — low hundreds of entries on
+the largest retail titles. 4096 leaves >20x headroom.
+
+`Decoder::push` (symbolic-stack push during binding `<clinit>` walking):
+honours the Code attribute's declared `max_stack`. JVMS 4.7.3 requires
+that a method's operand stack never exceed `max_stack` at any point, so
+a push past it can only come from bytecode that would fail JVM
+verification. Dropping it costs nothing on real bytecode and bounds the
+decoder: a `.class` gated only by a `com/bydeluxe/` path prefix deflates
+from ~100 KB to the 64 MiB `MAX_CLASS_BYTES` ceiling, i.e. ~67M
+single-byte `iconst_0` (~2 GiB of `StackVal`) on an unbounded `Vec`.
+Headroom: `max_stack` is exactly what javac computed for the real
+binding `<clinit>`, so no real construction can be clipped. The symbolic
+stack counts `long`/`double` as one slot where the JVM counts two, so
+its depth is never greater than the verified depth.
+
+## interpret_streams: Constructions -> StreamLabels
+
+Converts the per-construction tuples from Phase D into `StreamLabel`s.
+Two binding-constructor shapes are handled:
+
+- 5-arg: `BindingType.<init>(I, Lang;, Lpurpose;, I, LCodingType;)V`
+- 4-arg: `BindingType.<init>(I, Lang;, Lpurpose;, LCodingType;)V`
+
+Args are identified by **TYPE**, not position:
+
+- First `EnumRef{kind: "Language"}` -> audio/subtitle language
+- First `EnumRef{kind: "Purpose"}` -> Deluxe purpose ordinal
+- First `CodingType(name)` -> codec field name (translated via
+  `coding_type_to_codec_hint`)
+- First `Int(n)` -> stream index (preserved as ordering hint;
+  per-type sequential stream_number is what actually goes into the
+  StreamLabel, since BD spec stream-numbering is anchored on MPLS
+  data, not the binding code)
+
+Stream type inference:
+
+- Construction has a `CodingType` arg -> audio stream (subtitles on
+  Deluxe don't carry a CodingType; their codec is implicit PGS via
+  the BD spec).
+- Construction has Language but no CodingType -> subtitle stream.
+- Neither, and its binding type never yielded a stream -> not a
+  stream (skip). See `slot_kind` for why the binding type is
+  consulted rather than the language alone.
+
+`slot_kinds`: which stream list each binding type enumerates, learned
+from the constructions that DID resolve a language. A `<clinit>` walk
+emits a `Construction` for every `new X; ...; invokespecial X.<init>`
+it sees, so the list mixes real stream bindings with whatever else the
+class initializer builds. `binding_type` is the constructed class name,
+which is how the two are told apart: the stream bindings all share one
+class (Deluxe splits audio and subtitle across two), and that class is
+identifiable from the slots that resolved. A binding type that resolved
+as both kinds is left out — with no consistent answer, guessing a list
+to advance would be worse than not advancing.
+
+`slot_kind`: the stream list an unresolved construction occupies a slot
+in, or `None` when it is not a stream binding. A
+`org.bluray.ti.CodingType` argument is decisive on its own: nothing but
+an audio stream binding is handed one. Otherwise falls back to what the
+binding type's resolved siblings showed (`slot_kinds`).
+
+## Confirmed studio variants
+
+- **Universal** (`studio="uni"`): Language enum `pd` (65 values,
+  `English, French, Spanish, Dutch, …`), Purpose enum `lp`
+  (`Normal, Commentary, PiP, Trivia, Descriptive, Score`), audio binding
+  `np.<init>(I, Lpd;, Llp;, Lorg/bluray/ti/CodingType;)`, subtitle binding
+  `wb.<init>(I, Lpd;, Llp;, Lmi;)`, all built in one binding class's
+  `<clinit>` alongside a title-wrapper object whose constructor takes the
+  per-stream arrays (filtered out by the array-parameter guard in the
+  decoder). SDH/RNIB is encoded as a distinct Language VALUE
+  ("English SDH", "English RNIB"), recovered into the qualifier from the
+  name. Grounded on fixtures captured from a real Universal Blu-ray release.
+- **Disney/Warner**: 70-value Language enum, same binding shape; the
+  original corpus this parser was written against.

docs/demux-sink.md

@@ -0,0 +1,74 @@
+# `demux://` sink — per-codec ES output
+
+The `demux://` sink is a write-only `crate::pes::Stream`. Instead of muxing
+the per-track `PesFrame` stream into a single container (as `MkvStream`
+does), it routes each frame's payload to the file for `frame.track`,
+post-processing where the internal codec `Frame` form differs from the
+standalone on-disk ES form:
+
+- **HEVC / H.264**: the codec parsers emit hvcC/avcC-style 4-byte
+  length-prefixed NALs (start codes stripped) and carry the parameter sets
+  out-of-band in `codec_private`. A standalone `.hevc`/`.h264` needs Annex-B
+  framing with the parameter sets prepended — see `AnnexBWriter`.
+- **PGS**: the parser collapses a display/clear PCS pair into one
+  duration-bearing `Frame` with the raw segment payload but no `PG` magic /
+  timestamp header. A `.sup` needs the HDMV segment framing rebuilt — see
+  `PgsSupWriter`.
+- **VobSub**: the `.sub` is the raw SPU stream; the `.idx` sidecar is
+  synthesized from per-SPU PTS + byte offsets — see `VobSubWriter`.
+
+Every other codec writes `frame.data` verbatim (`PassthroughWriter`).
+
+The sink does NOT touch the MKV mux path; it is purely additive.
+
+## `PgsSupWriter`: rebuilding HDMV segment framing
+
+The parser hands the demux sink the concatenated PGS segments of a display
+set in `frame.data` (segment_type + segment_size + payload, repeated), with
+no `PG` magic and no PTS/DTS. A `.sup` prefixes each segment with a 13-byte
+header: `0x50 0x47` ("PG") | PTS u32 BE | DTS u32 BE | (segment_type|size
+already present in the payload). When the parser folded a trailing clear
+(`duration_ns` set), the writer re-emits it as an empty composition at
+`pts + duration` so players time the subtitle out.
+
+## `synthetic_clear_display_set`: synthesizing the clear PCS
+
+Builds a synthetic "clear" display set: an empty PCS (0 composition objects)
+followed by an END segment. The parser folds the original clear/end PCS
+pair's wipe time into the display frame's `duration_ns` and drops the clear
+bytes, so a faithful `.sup` re-emits one here at `display_pts + duration`;
+without it every subtitle lingers to EOF. `width`/`height` are carried from
+the display set's PCS so the clear PCS advertises the same video geometry —
+they don't affect the wipe but keep the segment well-formed. Returned bytes
+are concatenated `type(1)+size(2 BE)+payload` segments, the same shape
+`emit_segments` consumes.
+
+## Test: `epoch_driver_follows_ref_video_not_track_zero`
+
+Regression for the hardcoded `frame.track == 0` epoch driver: on an M2TS/PMT
+title the PMT can list an AUDIO ES before the VIDEO ES, so the video lands
+at stream index 1. The sink already resolves the video reference
+dynamically (`ref_video_track`); the epoch driver must use that SAME
+reference, not the literal 0. In the test, track 0 is audio and track 1 is
+video; a video-only clip boundary (track 1) must open a new epoch (bump
+`offset_ns`). With the bug (only `frame.track == 0` drives epochs) the
+video back-jump would be treated as a passive rider and `offset_ns` would
+stay 0 — corrupting every track's rebased timeline.
+
+## Test: `a_demux_export_the_seam_plan_emptied_fails`
+
+Audit finding: this sink builds its timeline with
+`TimelineContinuity::with_clips` but no test ever gave it a title with
+usable PlayItem marks, so `frames_mapped` and `dropped_total()` were always
+zero and BOTH gates in `finish` were unreachable. Deleting either left the
+whole suite green while a `demux://` export of a seamless-branching title
+wrote zero-byte track files beside a populated chapters document, at exit 0.
+
+## `sanitize`: path-hostile filename characters
+
+Control characters are replaced, NUL above all. Every string this touches is
+disc bytes, and a language code is three raw STN bytes run through
+`from_utf8_lossy` with no validation — `00 00 00` is the ordinary
+"undefined" encoding on real Blu-rays. A NUL in a path aborts
+`File::create` with `InvalidInput`, which took the whole demux export down
+before a single track file was opened.

docs/demux-thread.md

@@ -0,0 +1,65 @@
+# `DemuxThread`
+
+## Why a second worker thread
+
+With `crate::sector::PrefetchedSectorSource` alone, read+decrypt already
+runs on a producer thread; the *consumer* (main) thread still serialises
+`ts_demuxer.feed` (M2TS parsing) with the codec parsers. Profiling showed
+feed at ~37% and codec parse at ~44% of consumer wall time — i.e. feed is
+heavy enough that pipelining it with parse pays for itself.
+
+Splitting them: feed runs in `DemuxThread`; the consumer thread receives
+`Vec<PesPacket>` batches and runs codec parse + frame emission only. Total
+throughput becomes `1/max(feed, parse)` instead of `1/(feed + parse)`.
+
+## Lifecycle
+
+`DemuxThread::spawn_zero_copy` consumes the prefetch channels and the
+demuxer state, returning a handle plus a `Receiver<DemuxBatch>`. Dropping
+the handle closes the channel which signals the worker to exit; the join
+in `Drop::drop` blocks until the worker observes channel closure and
+returns (no timeout — a wedged downstream would block the drop until it
+releases the channel).
+
+## `spawn_zero_copy` rationale
+
+Instead of taking a `SectorSource` and memcpy-ing through its
+`read_sectors` API, this constructor consumes the prefetch channels
+directly: filled buffers come in via `prefetch_rx`, the demux thread
+feeds them, then returns them to `recycle_tx` for the producer to
+re-fill. Eliminates the 16 MiB memcpy per batch that the SectorSource
+adapter incurred (and, with the producer-side recycling pool, also
+eliminates the per-batch heap alloc / cross-thread free that was costing
+40%+ of demux-thread time before).
+
+## Test: empty-batch disconnect fix (`worker_exits_promptly_on_consumer_drop_during_empty_batches`)
+
+Regression: worker must detect consumer disconnect even when every demux
+batch is empty (no matching PIDs / null packets).
+
+Before the fix, `tx.send()` was never called for empty batches so the
+worker never observed the consumer drop — it would spin through ALL
+remaining extents before exiting, causing `DemuxThread::drop`'s `join()`
+to block for minutes on a mostly-untracked disc region.
+
+The watchdog: if the worker doesn't exit within 1s of the consumer drop
+the test fails (rather than hanging forever as the bug would).
+
+## Test: spawn-failure drop-order (`channels_disconnected_before_producer_join_on_spawn_failure`)
+
+Regression: on thread-spawn failure the channels must be dropped BEFORE
+the producer shell so the upstream producer observes disconnection and
+exits, allowing `join()` to complete without hanging.
+
+A true EAGAIN/pids-limit spawn failure cannot be reliably forced in a
+unit test without root or ulimit co-operation, so the test exercises the
+drop-order contract directly: a mock shell that panics if `join()` is
+called while either channel end is still open.
+
+The test constructs a `(prefetch_tx, prefetch_rx)` pair where the tx side
+is held by a sentinel that stays alive as long as either channel end is
+open, then asserts that the sentinel is gone by the time
+`producer_shell`'s join logic would run. Because a real spawn failure
+can't be forced, the test instead verifies the helper logic in isolation:
+drop `prefetch_rx` and `recycle_tx` first, then observe the producer-side
+sender is disconnected, which is the property the fix relies on.

docs/diag.md

@@ -0,0 +1,65 @@
+# diag.rs — scan diagnostics rationale
+
+## Why this module exists
+
+A bug report log must be self-diagnosing: everything needed to explain *why*
+freemkv made the choices it did at scan must be in the log, in a compact,
+machine-parseable form. `diag.rs` emits one terse line per row (title, cell,
+stream, decision) under the `tracing` target `freemkv::diag`, which the CLI
+routes to `log.txt` when `--log-level 3` (debug) is set.
+
+## Format conventions (stable, greppable)
+
+- Every line is prefixed by a `tag=` so a log scraper can filter (`disc`,
+  `title`, `dvd.cell`, `dvd.vattr`, `dvd.aattr`, `bd.clip`, `bd.mark`, `aacs`,
+  `stream`, `decision`).
+- Raw bytes are shown as `0xNN` next to their decode so a wrong decode is
+  obvious against the raw value.
+- This module only READS already-parsed scan state — it never re-reads the
+  disc and never mutates anything.
+
+## DVD per-cell table vs. Disc-level dump
+
+The DVD per-cell table (with the raw cell-category byte) is emitted from the
+IFO scan itself (`dump_dvd_cells`), because the per-cell `ifo::DvdCell` detail
+is lowered away before the `Disc` is built. The `Disc`-level dump
+(`dump_disc`) covers everything that survives lowering: titles, streams, the
+picked main feature, and AACS state.
+
+## `dump_dvd_substream_probe`
+
+Emits the ACTUAL per-physical-sub-stream AC-3 channel counts read off the VOB
+during the mux-time sub-stream probe (the Silence-of-the-Lambs wrong-stream
+fix). This is the ground truth the IFO nibble is compared against: each row is
+`sub_id=0x8x channels=N` for a physical `private_stream_1` AC-3 sub-stream
+whose first frame was decoded. An empty probe (scrambled / unreadable / short
+VOB) logs a single `probed=0` line so the absence is explicit in a bug log.
+
+Self-sufficiency: with `tag=dvd.aattr` (the IFO's declared sub_id + claimed
+channels) and these `tag=dvd.substream` rows (the physical reality), a bug log
+alone shows whether the ordinal `0x80` actually carries the declared channel
+layout — no disc needed to diagnose a wrong-substream rip.
+
+## `dump_mkv_track`
+
+Emits the MKV `TrackEntry` elements the muxer is about to WRITE for one track
+— the Windows-fps-class metadata (FlagInterlaced, FieldOrder,
+DefaultDuration, DefaultDecodedFieldDuration, Display dims) plus the
+codecPrivate as hex. With this row a bug log alone is enough to verify why
+Windows Explorer reports a given frame rate for an interlaced SD track: the
+container values that drive its fps derivation are all present, no disc and
+no MediaInfo needed.
+
+`track_number` is the 1-based MKV track number; `track` is the built
+`crate::mux::mkv::MkvTrack` whose fields map one-to-one onto the emitted
+elements (see `MkvMuxer::new`).
+
+## `main_feature_reason`
+
+The `reason=` token on the main-feature decision row is DERIVED from
+`Disc::CANONICAL_TITLE_ORDER_KEYS`, which lives beside the comparator that
+actually implements them — never restated here. The previous hand-written
+copy drifted (it advertised a `fewest-clips` key the comparator had replaced
+with largest-physical-size), which made the self-diagnosing log explain the
+pick with a rule the code does not apply. A diagnostic that disagrees with the
+decision it documents is worse than no diagnostic.

docs/dirimage-tests.md

@@ -0,0 +1,132 @@
+# Rationale for `src/dirimage/tests.rs`
+
+Longer-form notes for individual tests, referenced from `// See docs/dirimage-tests.md`
+pointers in the source so the inline comments stay within the comment-guard caps.
+
+## `Scratch::unique_path`
+
+The path a scratch dir takes is kept separate from directory creation so its
+uniqueness is testable without a syscall between draws. A monotonic counter,
+NOT a timestamp, is what guarantees it: `SystemTime::now()` resolves to only
+a MICROSECOND on macOS, so two of the seven parallel tests that share the
+"bdmv" tag routinely read the same value within one microsecond, collide on
+the same directory, and the first to finish `remove_dir_all`s it out from
+under the others' reads — an intermittent `read_sectors` ENOENT. The counter
+is unique regardless of clock granularity; pairing it with the pid keeps it
+unique across test-binary processes.
+
+## `scratch_paths_are_unique_even_at_clock_resolution`
+
+Every `Scratch` must own a DISTINCT directory. Seven tests share the "bdmv"
+tag and run in parallel; if two land the same path, the first to drop
+`remove_dir_all`s it out from under the other's reads, which surfaced as an
+intermittent `read_sectors` failure. Regression: with the old
+`SystemTime::now()` name this is RED, because macOS's clock advances only
+per microsecond, so a tight loop of pure draws — no `create_dir_all` syscall
+between them to nudge the clock, mirroring the real cross-thread collision —
+hands back the same value many times over. The counter-based name is unique
+regardless of clock granularity.
+
+## `a_directory_spanning_many_blocks_reads_back_whole`
+
+A directory with enough children that its FID list spans several 2048-byte
+blocks, read back through the production parser.
+
+This is the case the block-alignment question turns on: FIDs are packed
+contiguously and a descriptor may straddle a block boundary, because
+`read_directory` (`udf.rs:1312`) walks the directory extent as one flat byte
+run and BREAKS at the first non-257 tag. Padding each block would truncate
+the directory at the first pad. 200 entries also exceeds the 16-handle LRU
+several times over, so it exercises handle eviction on the read path.
+
+## `a_file_below_video_ts_is_placed_not_just_declared`
+
+A file inside a SUBDIRECTORY of `VIDEO_TS` must still have its data placed.
+
+Audit finding. The DVD branch places only the files directly inside
+`VIDEO_TS`, because only those carry the IFO-relative constraints — and the
+follow-up loop skipped that directory entirely, so anything one level deeper
+got a File Entry declaring the file's real size with no extents behind it.
+It appeared in the tree at full length and read back as nothing, at exit 0.
+The identical folder under `BDMV/` was always placed correctly, which is
+what made the gap easy to miss.
+
+## `a_vob_offset_past_the_image_cap_is_refused`
+
+A VOBS offset far past the content must be REFUSED, not honoured.
+
+Audit finding. The planner honours a title set's declared VOBS offset
+because honouring it is what makes a real backup readable, and nothing
+bounded it: a regenerated `.BUP`, a rewritten IFO or a hand-assembled folder
+naming a huge offset grew the image to wherever it pointed. A `u32` sector
+count reaches roughly 8.8 TB, and writing that to an `iso://` destination
+would fill a disk with zeros before anything noticed.
+
+The companion (`an_oversized_vob_offset_leaves_a_gap_rather_than_failing`)
+pins that a MODEST oversize is still honoured as a gap, so this cap refuses
+only what it must.
+
+## `playable_bdmv`
+
+A BD folder that really enumerates a title, so the AACS content probe has
+an extent to sample.
+
+The `.m2ts` is built as real 192-byte BD source packets, because that is
+what the probe judges: byte 0 carries the AACS Copy Permission Indicator in
+its top two bits, and byte 4 is the MPEG-TS sync. `scrambled` sets the CPI
+and withholds the sync — "flagged and not structurally clean", which is
+exactly `aacs_unit_needs_decrypt`. An all-zero payload would prove nothing
+either way: `is_clean_ts` skips zero payloads as padding.
+
+## `both_doors_agree_on_a_clear_folder_that_kept_its_aacs_directory`
+
+The two doors must AGREE. Same folder, same verdict, same extents.
+
+Stated as a differential rather than a bare `is_ok()` so it cannot go
+vacuous: if the fixture ever stops producing an AACS state, a one-sided
+`Ok` assertion would still pass while guarding nothing, whereas "both doors
+see the same title" is the invariant the shared function actually exists to
+hold.
+
+## `a_scrambled_folder_is_refused_through_the_dir_url_door_too`
+
+The other verdict, through the same door: a folder whose content units are
+really scrambled is refused with the TYPED code, not muxed into garbage.
+
+This is the load-bearing half. `E_DIR_IMAGE_ENCRYPTED` is produced at
+exactly one site in the crate (`session::apply_folder_encryption_verdict`),
+reachable from here only through the `is_folder` argument — so this test
+cannot pass if that argument is dropped, whatever else changes.
+
+## `write_and_mount_externally`
+
+Write a synthesized image to a real file and ask the OS to mount it.
+
+This is the only check here that is not circular: `read_filesystem` shares
+every assumption with the encoder, an operating system's UDF driver shares
+none of them. Ignored by default because it shells out to `hdiutil` and
+needs a host that can attach an image; run with
+`cargo test -- --ignored write_and_mount_externally --nocapture`.
+
+## `dvd_placement_invariant_on_a_real_folder`
+
+Diagnostic (opt-in): verify the DVD placement invariant for every title set
+in a REAL folder. `ifo.rs` derives a title's extents as
+`file_start_lba(VTS_nn_0.IFO) + vtstt_vobs`, so that sum must land exactly on
+`VTS_nn_1.VOB` or the mux reads the wrong sectors for that title.
+
+Run with: `FMKV_DVD_FOLDER=/path/to/tree cargo test --lib
+dvd_placement_invariant_on_a_real_folder -- --ignored --nocapture`
+
+## `a_multi_clip_playlist_produces_feed_spans_that_tile_the_feed`
+
+`Clip::feed_span` is the INPUT to the whole provenance feature — it is what
+tells the muxer which clip a byte offset belongs to — and it is produced in
+exactly one place, `disc/bluray.rs`. Every `SeamPlan` test synthesizes spans
+by hand, so the consumer is thoroughly tested against fixtures written from
+the same assumptions as the producer, and nothing checks the producer at all.
+
+That is the shape of the original defect: the placement logic was tested and
+correct, and the thing feeding it was wrong. `SeamPlan` only trusts spans
+that TILE the feed contiguously from zero, so this asserts exactly that,
+against the real scanner reading a real synthesized filesystem.

docs/dirimage.md

@@ -0,0 +1,185 @@
+# `dirimage` — `dir://` as an image-level source
+
+`dirimage` synthesizes a real, minimal, valid UDF 1.02 volume over a host
+folder (a DVD `VIDEO_TS/` or Blu-ray `BDMV/` extracted by a MakeMKV-style
+backup). Nothing is emulated:
+
+* **Metadata sectors** (anchors, the volume descriptor sequences, the File
+  Set Descriptor, every File Entry, every directory's FID list) are encoded
+  into RAM by `encode` — a few MiB even for a large Blu-ray.
+* **Data sectors** are not materialized at all. Each one maps to a byte
+  range of a real file, read on demand.
+
+So `udf::read_filesystem` parses this image by exactly the same code path it
+parses a real disc with, and every consumer above it is unchanged. The cost
+is that a single-partition synthetic volume never exercises the UDF 2.50
+Metadata Partition path (`udf.rs:946-991`) that every real BD-ROM uses —
+this module's tests do not cover that block and must not be read as if they
+did.
+
+## What this module deliberately does NOT do
+
+* **3D / SSIF** — rejected up front (`Error::DirImageSsifUnsupported`). An
+  SSIF aliases the same sectors as its base and dependent `.m2ts`; the
+  planner allocates disjoint extents, so a 3D folder would produce silently
+  wrong output.
+* **HD-DVD `HVDVD_TS/`** — no title enumerator constraint is modelled.
+* **Encrypted folders** — a folder whose content is still AACS-scrambled is
+  rejected by the caller-side probe, not decrypted here.
+
+## `layout.rs` — rationale detail
+
+Full detail for the comments trimmed in `src/dirimage/layout.rs`, in file order.
+
+**Module overview.** Two phases, kept apart because they fail for different
+reasons: walk rejects what the image model cannot represent (3D SSIF, an
+unrecognized tree, a case collision inside one directory); assign places
+metadata first (File Set Descriptor, one File Entry per node, then the
+directory FID lists), then file data. Data placement is the part with real
+constraints. For a Blu-ray there are none — `.mpls`/`.clpi` address clips by
+name, never by LBA — so files are packed sequentially. For a DVD the IFOs
+record VOB positions as sector offsets from the IFO's own start, and `ifo.rs`
+re-derives every title extent from them, so the placement must reproduce
+those offsets exactly or the rip reads the wrong sectors (`place_video_ts`).
+
+**`DATA_FLOOR`.** Well clear of the volume-space descriptors, and — the
+load-bearing part — far from zero: `disc/bluray.rs:137` drops any clip extent
+whose LBA is 0, so a file that landed at block 0 would vanish from the title
+with no error.
+
+**`MAX_AD_BYTES`.** The AD length field is 30 bits (the top two are the
+ECMA-167 4/14.14.1.1 extent type), so 0x3FFF_FFFF is the arithmetic ceiling —
+but a non-final extent must be a whole number of blocks, so the usable
+ceiling is the largest multiple of 2048 below it. Files larger than this are
+split across several ADs; `udf.rs` reads them back as a multi-extent file,
+the same shape a dual-layer disc produces.
+
+**`MAX_DEPTH`.** Matches `udf.rs`'s `MAX_DIR_DEPTH`: anything deeper would be
+recorded but never descended into, so the files under it would be invisible
+to every consumer. Refuse instead of silently dropping.
+
+**`MAX_CS0_NAME_BYTES`.** The FID's name-length field is one byte, so 255 is
+the ceiling; 254 leaves the encoder no way to produce a value that wraps to
+zero.
+
+**`MAX_SUBDIRS`.** A directory File Entry's link count is `u16` and counts
+one per child directory plus one for its own entry in the parent, so the
+last usable value is `u16::MAX - 1`. Lowered under `cfg(test)` ONLY so the
+guard can actually be executed: building a folder with 65534 subdirectories
+to reach the real cap is not a test anyone can run, so an earlier test
+asserted arithmetic about the constant instead and would have passed with
+the guard deleted. The production value is unchanged.
+
+**Module-scope link-count assert.** Must live at module scope, not inside
+`mod tests`: it previously sat inside `#[cfg(test)] mod tests` while also
+carrying its own `#[cfg(not(test))]`, so it was compiled in NO configuration
+and could never fire — exactly the dead gate the test above it was written
+to replace.
+
+**`MAX_IMAGE_SECTORS`.** A DVD title set records where its VOBS begins as an
+offset in its own IFO, read verbatim out of a file in the folder. A
+regenerated `.BUP`, a tool that rewrote an IFO, or a hand-assembled folder
+can therefore name an offset far beyond the content — and the planner
+honours it, because honouring it is what makes a real backup readable.
+Without a ceiling the image grows to wherever that offset points: a `u32`
+sector count reaches ~8.8 TB, and writing one to an `iso://` destination
+would fill a disk with zeros before anything noticed. 128 GiB clears the
+largest real medium (BD-100) with room to spare, so a genuine disc folder
+never meets it.
+
+**`MAX_META_BYTES`.** Every node costs a 2 KiB File Entry sector held for the
+life of the image, so the entry cap alone permits ~205 MB of metadata for
+content of no size at all — and the mux holds two of these at once while
+probing. The module documents a budget of "a few MiB even for a large
+Blu-ray"; this is what enforces it rather than merely asserting it.
+
+**`is_excluded`.** Dot-files are host artefacts, never disc content: macOS
+sprays `.DS_Store` and `._*` resource forks through any folder a Finder
+window has touched, and including them would put files on the "disc" that
+were never on the disc. `.partial` is freemkv's own in-flight extraction
+suffix (see `disc/extract.rs`) — picking one up would mean planning an
+extent over a file that is still being written.
+
+**`read_head`.** Reads the first `n` bytes of an IFO so its placement
+offsets can be resolved. Errors propagate: returning an empty buffer instead
+would send every offset through `unwrap_or(0)`, recording NO placement
+constraint, and a VOB placed without its constraint yields an image that
+reads at the wrong offset with nothing reported. An IFO that cannot be read
+is a folder that cannot be planned.
+
+**`place_video_ts`.** DVD-Video records VOB positions INSIDE the IFOs, as
+sector offsets from the IFO file's own first sector: `VIDEO_TS.IFO` + 0xC0
+(`VMGM_VOBS`) → `VIDEO_TS.VOB`; `VTS_nn_0.IFO` + 0xC0 (`vtsm_vobs`) →
+`VTS_nn_0.VOB` (the VTS menu); `VTS_nn_0.IFO` + 0xC4 (`vtstt_vobs`) →
+`VTS_nn_1.VOB` (the title stream). `ifo.rs:554-556` re-derives every title
+extent as `file_start_lba(IFO) + vtstt_vobs + cell.first_sector`, so only the
+third of those is load-bearing for freemkv itself — but the other two are
+load-bearing for DVD PLAYERS, which read the menus freemkv ignores. All
+three are honoured. `VTS_nn_1.VOB … VTS_nn_9.VOB` are one logical stream
+split at the 1 GB file-size limit, and the cell sector addresses run
+continuously across the split, so they are placed back-to-back with no gap;
+laying the group out in its canonical on-disc order gives exactly that for
+free, so the constraint becomes a CHECK, not a search. The check can fail —
+a regenerated `.BUP`, a tool that rewrote an IFO, a folder assembled by hand
+— and when it does the required position lies below the end of the file
+that must precede it. There is no placement that satisfies it, so it is a
+typed error naming the file rather than a silent misplacement.
+
+**`reject_ssif`.** `disc/bluray.rs:124-130` probes
+`/BDMV/STREAM/SSIF/{clip}.ssif` and sets `is_3d` the moment one resolves —
+unconditionally, before any capability check. On a real 3D disc the `.ssif`
+and the base/dependent `.m2ts` files ALIAS the same sectors (the SSIF
+interleave IS the two m2ts streams), which this planner cannot express: it
+would allocate three disjoint copies, so the clip's extents and the m2ts's
+extents would disagree and the rip would read the wrong bytes at exit 0.
+Reject the folder instead.
+
+**`plan` — capacity, and what it changes.** `total_sectors` becomes the
+`Disc`'s `capacity_sectors` / `capacity_bytes`, and `capacity_bytes` is not
+inert: `canonical_title_order`'s oversize gate (`disc/mod.rs:2039-2040`, body
+`:2209-2210`) demotes any title whose `size_bytes` exceeds it, which decides
+which title sorts first and therefore what `-t 1` selects. The capacity
+reported here is **the synthesized image's own size** — what an ISO built
+from this folder would report — and nothing else. It is NOT padded up to a
+media tier (BD25/BD50/…): that was considered and does not work, since a
+folder does not record the tier of the disc it came from, so a 22 GB folder
+off a BD50 would pad to BD25 and diverge anyway, and the padding would
+inflate any pre-sized output written from the image. The consequence, stated
+plainly: **for a folder that is missing files the source disc had — a
+selective MakeMKV backup being the normal case — the capacity is smaller
+than the source disc's, the oversize gate is therefore stricter, and a
+borderline "play-all" composite title that the ISO kept can be demoted here.
+`-t 1` can select a different title from `dir://FOLDER` than from an
+`iso://` of the same disc.** For a complete folder the two agree, because
+the capacities agree. This is chosen over the alternatives because it is the
+only one that is self-consistent: `dir://X` and an `iso://` built from `X`
+describe the same image and must answer the same way.
+
+**Tests.**
+* `a_file_past_the_ad_ceiling_splits_on_a_block_boundary` — a file above the
+  30-bit AD ceiling must split into MULTIPLE descriptors, and every
+  non-final one must be a whole number of blocks, or the next extent's bytes
+  start mid-sector and the file reassembles wrong. Kills a mutant that emits
+  one oversized AD (whose length would collide with the extent-TYPE bits
+  `udf.rs:642` reads).
+* `two_names_the_reader_cannot_tell_apart_are_refused` — audit finding: the
+  uniqueness check compared raw host names, while `parse_udf_name` trims
+  whitespace and drops code units `char::from_u32` rejects. So
+  " 00000.m2ts" and "00000.m2ts" were two distinct entries at plan time and
+  ONE name at read time; `find`/`read_file` take the first match, so a title
+  resolved to the wrong file's extents and muxed the wrong bytes at exit 0.
+  Calls `plan` on a real folder and fails if the round-trip key is reverted
+  to comparing host names.
+* `an_over_long_name_is_refused_by_the_planner` — audit finding: the length
+  was narrowed with `as u8`, so a 255-byte ASCII name (POSIX NAME_MAX, legal
+  on ext4/APFS/NTFS) encoded to 256 bytes with the CS0 compression byte and
+  wrote a length of ZERO, making every later entry in that directory read
+  from the wrong offset. An earlier version of this test asserted arithmetic
+  about the constants and never called `plan`, so it would have passed with
+  the guard deleted.
+* `the_subdir_cap_refuses_a_folder_with_too_many_subdirectories` — pins the
+  arithmetic relationship the guard relies on and executes the guard rather
+  than restating the constant: link count (child dirs + 1) is 16 bits, so
+  exceeding it wraps and the image lies about its own directory structure.
+  Creating 65,535 directories in a test is not reasonable, so this does NOT
+  exercise `walk`.

docs/disc-mod.md

@@ -0,0 +1,462 @@
+# src/disc/mod.rs — internal notes
+
+Overflow rationale for internal (non-`pub`) items in `src/disc/mod.rs`,
+relocated here by the comment-guard so the in-file comment can stay short.
+Each section is pointed to by a one-line `// See docs/disc-mod.md — <topic>`
+comment at the corresponding call site.
+
+## aacs_dir_present
+
+THE ONE definition of "is this disc structurally AACS-encrypted". Both
+`Disc::identify` (fast path, filesystem only) and `Disc::scan_with` (full
+scan) need this, and both used to spell out the same two `find_dir` calls by
+hand. They agreed today; nothing made them agree tomorrow — adding a third
+AACS location, or excluding an empty placeholder directory, to one copy and
+not the other would silently desync the fast identify from the full scan (the
+same disc reported encrypted by one and clear by the other).
+
+This is STRUCTURAL, not cryptographic: it says the tree looks like an
+encrypted disc, not that any sector actually is. A folder copied verbatim
+from a decrypted disc keeps its `AACS/` and answers true here (see
+`session::scan_dir`, which corrects for exactly that).
+
+## correct_truehd_channels
+
+Corrects a title's TrueHD audio-stream metadata by probing the first
+decrypted access units — channel count, real sample rate, and Atmos detection
+in a single major-sync read. The MPLS descriptors declare the BASE layout
+(often 5.1, or a container-guessed rate) even for a 7.1/Atmos TrueHD track;
+the truth is in the MLP major sync. `reader` must yield DECRYPTED sectors
+(the m2ts is AACS-encrypted, so this can only run at mux time, not scan).
+Reads a bounded window of the title's first extent.
+
+Corrections, each individually guarded so a malformed field never writes a
+wrong header:
+- **Channels**: from the presentation channel masks (as before).
+- **Sample rate**: from the whitelisted rate nibble; left untouched on an
+  unknown rate or no major sync.
+- **Atmos**: when a 4th substream is detected AND the stream still carries
+  the basic descriptor label, the label is promoted to the Atmos form;
+  richer editorial labels (e.g. an existing "Dolby Atmos") are left intact.
+
+## Resolution::pixels
+
+`Unknown` deliberately does NOT fabricate a plausible 1920x1080. This is the
+same trap already closed on `AudioChannels::count` (which used to return 6)
+and `SampleRate::hz` (48000.0): a plausible wrong answer is indistinguishable
+from a real one at every call site, so a caller can forget to check the
+variant first — the `json://` sink had already walked into exactly that,
+reporting confident dimensions for a stream whose neighbouring `resolution`
+field said "unknown".
+
+It also does not return `(0, 0)`: that shape looks like a usable pair, so the
+MP4 sink stored it and serialised a 0x0 video track — a structurally complete
+file no player can render, written with no error. Before that it returned a
+fabricated 1920x1080, which was wrong but at least playable, so the sink had
+never needed a guard and the absence of one was invisible. A doc comment
+listing which callers are safe cannot hold this: one did not check, and a
+third kept its own duplicate `Unknown` test long after the accessor took the
+job over. `Option` forces every caller to make its OWN decision: Matroska
+omits the optional PixelWidth/PixelHeight elements, the metadata sinks report
+the dimensions as absent, and MP4 must refuse per ISO/IEC 14496-12 (width and
+height are mandatory in both `tkhd` 8.3.2 and VisualSampleEntry 12.1.3).
+
+## has_probable_video
+
+The exposed `streams` come from the title's FIRST PlayItem only, so a
+feature whose first PlayItem is a non-video bumper reports
+`has_video() == false` and would be wrongly disqualified (audit R6). This
+predicate is deliberately MORE permissive than `has_video` — it only ever
+ADMITS a title the stricter gate would reject — so it cannot reopen the
+decoy hole: a size-inflated streamless decoy is demoted STRUCTURALLY by
+composite detection in `Disc::rank_titles`, not by this gate, while it still
+rejects tiny streamless menu/metadata playlists. The size fallback requires
+at least one clip, so a clip-less pure-metadata decoy (which cannot be a
+real bumper-lead feature — that has the feature clip) is still rejected.
+
+## image_crack_extents
+
+The extents an image-time CSS crack scans, in the crate's CANONICAL order:
+the main feature's own extents, in natural playback order. Both halves are
+deferred to logic the crate already owns rather than re-derived here:
+
+- WHICH title — `scan_with` has already sorted `titles` with
+  `Self::canonical_title_order`, so the canonical main feature is the first
+  title that actually has extents. No local pick.
+- WHAT ORDER — playback order, i.e. the extent vector untouched, exactly as
+  `Self::decrypt_keys_for_title` hands `&title.extents` to
+  `css::crack_key_outcome`.
+
+**Why this function exists (do not let the copy grow back):** `Disc::scan_image`
+used to re-implement both halves inline — it picked the title with the
+largest total sector count, then re-sorted that title's extents
+LARGEST-CELL-FIRST before handing them to `crack_key_outcome`. Both had
+drifted from the canonical rules:
+
+- Largest-cell-first is the 1.5.1 garbage bug. A CSS DVD's biggest cell opens
+  with a long CLEAR run, and the crack's 50_000-sector budget is shared
+  across the whole extent list, so starting there can exhaust the budget
+  without ever reaching a scrambled sector — the crack reports `Unencrypted`
+  and the mux emits scrambled MPEG as plaintext. Playback order reaches the
+  scrambled feature body after only the small clear front matter that
+  precedes it on a real disc (CSS: the title key is recovered from the
+  scrambled data itself, so the scan must actually MEET scrambled data).
+- The sector-count pick ignores `canonical_title_order`'s capacity gate, so
+  it selects the oversize "play-all" composite (whose declared cells
+  double-count data shared with other playlists) instead of the real feature
+  — i.e. a DIFFERENT title, and on a multi-VTS disc a different VTS, whose
+  CSS title key does not descramble the feature at all.
+
+The result: the same disc cracked as an ISO could disagree with the same
+disc cracked from the drive, which is precisely what the duplicate was free
+to do. Keep the derivation here, shared, so it cannot recur.
+
+## read_aacs_inputs_from_reader
+
+Reads a disc's AACS key-input files from a sector source: returns
+`(Unit_Key_RO.inf, MKB)` raw bytes. Shared body for `Disc::read_aacs_inputs`
+(ISO) and `Disc::read_aacs_inputs_from_drive` (live drive). Prefers MKB_RO,
+falls back to MKB_RW, then TRIMS to the real record length. Both files are
+allocated to a fixed ~128 MiB and zero-padded, so reading either ships up to
+~124 MiB of nothing — trim to the record stream so callers send/store a few
+MB, not 128 MiB.
+
+## read_aacs_version
+
+AACS major version (`crate::aacs::mkb::AACS_MAJOR_BD` /
+`crate::aacs::mkb::AACS_MAJOR_UHD`) from the content certificate. Drives the
+`Unit_Key_RO.inf` parse stride (48-byte V10 vs 64-byte V20/V21), so the
+out-of-band key-fetch path parses `enc_title_keys` at the right stride (a
+server VUK then derives the correct unit keys).
+
+When no content certificate is readable/parseable, defaults to **UHD (V20,
+64-byte stride)** — the conservative choice the pre-1.2.0 fetch path
+hardcoded — and logs it: a wrong stride here folds a server VUK against
+mis-strided title keys (silent wrong unit keys), so a missing cert must not
+quietly pick the V10 stride for a UHD disc.
+
+## read_mkb_content
+
+Reads the AACS MKB's real record stream — NOT its zero padding. `MKB_RO.inf`
+/ `MKB_RW.inf` are allocated to a fixed ~128 MiB and zero-padded; the actual
+record stream is a few MiB. Reads a bounded prefix, finds the record-stream
+length via `crate::aacs::mkb::mkb_content_len` and returns exactly that,
+growing the prefix if the records run past it. This avoids reading 100+ MiB
+of padding on every scan AND avoids the `read_file` `MAX_FILE_BYTES` cap that
+(since 0.31.0) rejected the padded 128 MiB MKB outright — which made
+`read_aacs_inputs` fail and autorip report "could not read this disc's key
+files" without ever contacting the keyserver.
+
+## CANONICAL_TITLE_ORDER_KEYS
+
+**Why not just sort by duration descending?** Branching UHDs (and some BD
+authoring) ship a "play-all" virtual playlist that references the same
+source clips multiple times for seamless alternate-angle / alternate-ending
+playback. Those playlists report an inflated `duration_secs` (often 4+
+hours) and an inflated `size_bytes` greater than the disc's physical
+capacity. Example seen in the wild — *The Amateur (2025)* UHD, 58.5 GB
+BD-100 disc:
+
+| Title | Playlist   | Duration | Size    | Clips |
+|-------|------------|----------|---------|-------|
+|   1   | 00020.mpls | 4h 13m   | 92.4 GB |  253  |
+|   2   | 00800.mpls | 2h 02m   | 57.2 GB |    1  |
+
+Title 1's 92.4 GB cannot fit on a 58.5 GB disc unless the same clip data is
+referenced multiple times — proof it's a virtual composite. A duration-only
+sort would put it at `titles[0]`, so `freemkv -t 1`, `disc.titles.first()`,
+and autorip's main-feature picker all grab the 4-hour composite instead of
+the 2-hour movie that actually matches TMDB.
+
+**Effect on non-branching discs:** unchanged — the main movie is already the
+longest 1-clip title. **Effect on branching UHDs:** the virtual play-all
+playlist is pushed to the back, the actual movie surfaces at index 0.
+
+Defined immediately beside the comparator, so a diagnostic can NAME the
+ordering instead of restating it. The `freemkv::diag` main-feature decision
+row used to carry its own hand-written copy of this list, and it drifted: it
+still advertised a `fewest-clips` key long after the comparator replaced
+clip-count with largest-physical-size, so the `--log-level 3` bug-report log
+explained freemkv's top-level pick with a rule freemkv does not apply. Any
+change to the keys must change this list in the same edit.
+
+## probe_forced_subtitles_for_bdts_titles
+
+Pulled out of `scan_with` as its own callable predicate: the decision is
+otherwise reachable only by driving the full scan pipeline (tree dispatch ->
+title parsing -> this loop), so a test could not pin the gate without also
+authoring an entire synthetic disc image. Running it against an HD-DVD/DVD
+(`MpegPs`) title's extents would demux the wrong container, since only
+`BdTs` titles carry PES-wrapped PGS the shared classifier
+(`pgs_forced_probe`) understands.
+
+## MAIN_FEATURE_ORDER_KEYS
+
+- `nav-feature`: the title the disc's own HDMV navigation plays as the
+  feature, resolved by running First-Play in the `crate::bdnav` VM the way a
+  real player would. This is the authoritative, size-independent pick; it is
+  video-gated (a mis-resolve cannot select a streamless playlist) and simply
+  absent when the VM abstains (BD-J discs, or non-convergence), in which
+  case the lower keys decide.
+- `authoring-feature`: a title the disc's own menu authoring designates as
+  the feature (has video, is not itself a composite, and is within a sane
+  fraction of the longest title's duration) outranks everything else — a
+  size-independent signal an obfuscation decoy cannot forge.
+- `standalone`: a title that is a play-all / wrapper COMPOSITE — its clip
+  set properly contains another substantial video title's whole clip set (a
+  real UHD title's decoy playlist `00245` = `[bumper][00001 feature
+  clip][outro]` case) — is demoted below the standalone title it wraps. This
+  is the STRUCTURAL anti-decoy signal; it does not depend on stream counts,
+  physical size, or disc capacity, so it survives where those are spoofed or
+  unknown.
+- `has-video`: a title with no plausible video content (see
+  `DiscTitle::has_probable_video`) is demoted below every title that has
+  some — a floor that drops streamless menu/metadata playlists.
+
+## rank_titles
+
+This catches both the wrapper decoy (`00245 ⊋ 00001`) and the oversize
+play-all — independent of capacity, which the `fits-disc` gate needs and
+which is `0`/unknown on drives that fail READ CAPACITY. The corpus
+title-selection gate is the backstop across the disc hoard for the known
+residual (a real feature with a separate "resume from the middle" branch
+playlist reusing most of its clips).
+
+## aligned_unit_keys_validate
+
+Conservative: a sample that is not AACS-scrambled proves nothing, and with
+no scrambled sample at all there is nothing to disprove against, so it
+returns `true` (accept). It returns `false` when ANY scrambled sample cannot
+be restored to clear MPEG-TS by ANY unit key in the set. That covers two
+distinct failure shapes: (1) a wholly wrong key (a keydb VK that does not
+match this disc) — no sample decrypts; and (2) a *partially* applicable key
+set on a multi-CPS-unit disc — the resolved keys cover CPS unit 0 but not
+CPS unit 1. Accepting on the first sample that decrypts (the old behaviour)
+would commit such a set, after which CPS-unit-1 sectors pass through as raw
+encrypted bytes into the ISO/MKV with no error surfaced anywhere. Requiring
+every scrambled sample to decrypt rejects the incomplete set so the caller
+falls through to the next candidate. Reuses the ecosystem's single
+`is_clean` content-clarity predicate and the full (bus + AACS) unit decrypt,
+so it agrees with the actual mux decrypt.
+
+## ensure_decryptable
+
+The verdict, in order:
+- `raw == true` → `Ok(())`. `--raw` intentionally skips decryption and needs
+  no key (the caller wants an encrypted image).
+- `self.css_error.is_some()` → `Err(Error::CssNoDiscKey)`. The scan saw
+  scrambled CSS sectors but recovered no title key (`self.css` is `None` yet
+  the content IS encrypted). Treating `css.is_none()` as "unencrypted" would
+  mux scrambled MPEG as plaintext garbage. A DISC-LEVEL verdict
+  (`error::is_disc_level_no_key`) — the main feature's crack failed, so
+  every title fails the same way and the rip loop must stop rather than
+  skip each title in turn.
+- AACS-encrypted (`self.aacs.is_some()`) with no usable key
+  (`decrypt_keys()` is `None`) → `Err(Error::NoDiscKey { .. })`, naming the
+  disc by hash.
+- CSS-encrypted (`self.css.is_some()`) with no usable key →
+  `Err(Error::CssKeyMissing)`. (The disc-wide `decrypt_keys()` yields
+  `Css{..}` whenever `css.is_some()`, so this is defensive; the live
+  multi-VTS case is gated by `Self::ensure_decryptable_keys`.)
+- otherwise → `Ok(())`. A genuinely unencrypted disc has `None` keys
+  legitimately, and a CSS disc whose keyless crack succeeded has a key.
+
+## decrypt_keys_for_title
+
+For a DVD the CSS title key MUST be recovered before descrambling: a
+scrambled sector without a recoverable crib cannot self-crack, and CSS
+leaves the pack/PES header clear, so a sector left un-descrambled would mux
+as a structurally-valid but corrupt PES packet with no loss reported. Two
+ways to get it:
+
+- **Fast path** — the scan already cracked a key whose LBA span
+  (`crate::css::CssState::crack_span`) covers this title's VTS: reuse it. No
+  re-read, and on a live drive no second CSS bus-auth round-trip. CSS title
+  keys are per-VTS, so an overlapping span is the same key.
+- **Crack** — when up-front detection missed (`self.css == None`) or the
+  title lives in a different VTS: crack the key from this title's OWN
+  extents in a SINGLE scan, in natural PLAYBACK ORDER (never
+  largest-cell-first, which starved the crack in a big cell's clear prefix —
+  the 1.5.1 bug). Playback order reaches the scrambled feature body after
+  only the small clear front matter (logo / rating card) that precedes it.
+  One scan = one CSS-locked early-bail, so a locked title is not
+  re-hammered per cell against a live drive (hard rule #2); its 50k-sector
+  budget is the same accepted bound the disc-wide scan uses.
+
+Outcomes (`batch_sectors` sizes the crack's batched reads):
+- `(Css{title_key}, false)` — descramble with the recovered/reused key.
+- `(None, true)` — a genuinely-clear title needs no key; the gate passes it.
+- `(None, false)` — scrambled but no key recoverable → hard failure via
+  `Self::ensure_title_decryptable`, never a silent garbage mux.
+
+## inject_unit_keys
+
+Injects pre-resolved AACS unit keys into a scanned disc — the deferred-mux /
+resume path. The keys come from the mapfile's `# freemkv-uk:` header
+(persisted at sweep time when the disc was keyed), so the mux decrypts
+directly with NO key-service round-trip. Populates `self.aacs.unit_keys` so
+`Self::decrypt_keys` returns them and marks the source `ExternalUk`.
+
+If the scan built no AACS state (`self.aacs == None`) — which happens when
+the keydb was absent at scan time (`scan_aacs_no_keydb` ->
+`aacs_error = KeydbLoad`) — this synthesizes a minimal `ExternalUk` state
+for an encrypted AACS disc. A Unit Key is the FINAL per-title decryption
+key; the keydb is only needed to *derive* it, and that derivation already
+happened at sweep (the UK is in the mapfile). So a UK alone is sufficient to
+decrypt the on-disk ISO — AACS 2.0 bus decryption was applied by the drive
+at read time, so `read_data_key` is unused for file-backed mux. Without
+this, a keyed disc swept without a keydb would recover its UK yet still
+report E8005 (no usable `decrypt_keys`) at remux. No-op for an unencrypted
+or CSS (DVD) disc.
+
+## scan_with_passes_the_halt_flag_to_the_bluray_enumerator
+
+Every BD and DVD cancellation test in this crate calls
+`scan_bluray_titles` / `scan_dvd_titles` DIRECTLY, so the three-line wiring
+in `scan_with` that connects the operator's Stop to them was covered by
+nothing at all: replacing `opts.halt.as_ref()` with `None` on either branch
+left the whole suite green while a Stop during a BD or DVD scan silently did
+nothing. Only the HD-DVD branch was pinned.
+
+The fixture is deliberately the smallest disc that takes the BD branch — a
+bare `/BDMV` with no PLAYLIST — because the point under test is the
+ARGUMENT, not the enumerator's own (separately tested) halt polling. Nothing
+between `scan_with`'s entry and the enumerator reads the flag (the disc is
+unencrypted, so the AACS path is skipped), so a green here can only mean the
+flag arrived. Mutation: `Self::scan_bluray_titles(reader, &udf_fs, None)?`
+fails here.
+
+## halted_reads_do_not_report_the_hddvd_scan_as_successful
+
+A Stop on a LIVE DRIVE never touches `ScanOptions::halt`: `Drive` has its
+own flag and `checked_exec` fails every SCSI command with `Error::Halted`
+once it is set. The HD-DVD enumerator must not swallow that into a
+successful scan. Measured before this was fixed: the scan returned `Ok`
+with both titles present and ZERO streams on each — a cancelled scan
+wearing the shape of a disc whose clips carry no video or audio. Downstream
+that is a title list to cache, display and rip from.
+
+## scan_with_capacity_bytes tests
+
+`scan_with`'s `capacity_bytes = capacity as u64 * 2048` feeds
+`canonical_title_order`'s "bigger than the whole disc = play-all composite"
+threshold.
+
+`..._not_addition`: chosen so `capacity * 2048` clears both titles (neither
+is oversize, so the bigger one — OTHER — ranks first), but
+`capacity + 2048` lands BETWEEN the two sizes: MAIN stays non-oversize while
+OTHER flips to oversize and gets demoted, changing `titles[0]`. A `*` -> `+`
+mutation is caught by this ranking flip, not merely a wrong numeric
+threshold value.
+
+`..._not_division`: same mechanism, tuned to catch a `*` -> `/` mutation
+instead: `capacity * 2048` clears both titles, but `capacity / 2048`
+collapses to a threshold far below MAIN's declared size while still leaving
+MAIN under it, so only OTHER flips to oversize.
+
+## read_mkb_content_grows_prefix_past_16mib_when_records_run_longer
+
+This fixture's record stream is deliberately built so the first 16 records
+land EXACTLY on the 16 MiB boundary (so the 16 MiB prefix alone parses as a
+clean, complete record stream — the case a naive "n < buf.len() means done"
+check would wrongly accept) and 4 more MiB of records follow, terminated by
+the explicit `00 000000` end marker. Only a caller that actually grows past
+16 MiB recovers the true 20 MiB content length.
+
+## main_feature_order_demotes_wrapper_composite_decoy
+
+The decoy `00245.mpls` is a WRAPPER COMPOSITE — `[00339 2s bumper][00001 the
+whole feature clip][00336 outro]` — so its first-PlayItem STN reports v=0,
+and it is the LONGEST and LARGEST title (8350s / 78.4 GB vs the feature's
+8038s / 76.5 GB). Muxing its zero frames produced E6008 forever. It must be
+demoted STRUCTURALLY (its clip set properly contains the feature's), not by
+the fragile first-PlayItem stream count — this is what makes the fix robust
+to the video-bearing-composite variant (see
+`main_feature_order_demotes_video_composite`).
+
+## key_source_failure_is_not_reported_as_a_missing_disc_key
+
+Drives the real chain end to end — `KeySource` -> `resolve_and_apply_traced`
+-> `Disc::aacs_error` -> `ensure_decryptable` — twice over the SAME disc,
+and asserts the two operator-visible verdicts differ:
+
+- source returns `Err(KeyServiceUnavailable)` (the HTTP-502 outage) → E7028
+  "the key service could not answer; retry later",
+- source returns `Ok(vec![])` (the service answered, no entry) → E7022 "no
+  key source has a decryption key for this disc".
+
+The credential and rate-limit verdicts are asserted alongside, since each is
+a different operator action (fix the token / back off).
+
+## css_disc_wide_no_key_is_disc_level_while_per_title_stays_skippable
+
+The two CSS no-key conditions are NOT the same verdict and must classify
+oppositely through the public predicates:
+
+- **disc-wide** — `css_error` is set: the MAIN feature's crack failed, so
+  every title of this disc fails identically. Must be
+  `crate::error::is_disc_level_no_key` (the rip loop fail-fasts) and must
+  NOT be `crate::error::is_skippable_title_stub`. While both conditions
+  shared `E_CSS_KEY_MISSING`, an uncrackable CSS disc iterated all N titles
+  logging "title skipped" and exited 0 — a total failure reported as
+  success.
+- **per-title** — one title's own re-crack failed on a multi-VTS disc
+  (`title_is_clear == false`, no key): skipping it and finishing the rest is
+  correct policy, so it must STAY skippable and must NOT be disc-level.
+
+Pinned in both directions so a future change cannot silently flip either.
+
+## correct_truehd_channels_full_correction_and_atmos_promotion
+
+Kills the `was_basic ==`, the channels/rate `!=`/`&&` guards' "already
+correct" branch, the `!matches!` per-stream skip, the `is_atmos ==
+Some(true)` branch, and the whole-function no-op mutant.
+
+## byte_offset_in_title_accumulates_across_extents
+
+Kills: `lba >= start && lba < end` flipped to `||` (the first extent's
+disjunction would trivially match almost any lba and return the wrong,
+too-early offset); `cumulative +=` flipped to `*=` (cumulative is seeded at
+0, so `*=` freezes it at 0 forever); and `sector_count * SECTOR_BYTES_U64`
+flipped to `+` or `/` (wrong per-extent byte length folded into cumulative).
+
+## chapter_at_offset_concrete_arithmetic
+
+Kills: the `/` (time-fraction) flipped to `%` or `*`; the `*` (duration
+scale) flipped to `+`; the `<=` chapter-scan comparison flipped to `>`; the
+final `chapter_idx + 1` flipped to `-` or `*`; and every whole-function
+fixed-tuple replacement (none produce `(2, 60.0)`).
+
+## locate_ranges_positive_bps_duration_and_at_risk
+
+Kills `bps > 0.0` flipped to `==`/`<` (both would take the `else 0.0`
+branch here, wrongly reporting 0); `(*size as f64) / bps` flipped to `%` or
+`*`; and the trailing `* MILLIS_PER_SEC` flipped to `+` or `/`.
+
+## decrypt_keys_for_title_css_span_reuse_is_half_open
+
+A CSS title key is per-VTS: reusing the scan's cracked key for a title that
+lives OUTSIDE the cracked span descrambles that title with the wrong key,
+and the mux emits garbage at exit 0. `crack_span` is documented as the
+half-open LBA span `[start, end)`, so overlap is `extent.start < span.end &&
+span.start < extent.end` — both comparisons STRICT. A title that merely
+ABUTS the span (ends exactly where it begins, or begins exactly where it
+ends) shares no sector with it and must NOT reuse the key.
+
+The reader serves only clear (all-zero) sectors, so a title that falls
+through to its own crack is reported unencrypted — distinguishable from the
+reused-key answer both in the key and in the is-clear flag.
+
+## merge_content_key_ranges
+
+Merges per-title AACS key ranges into the sorted, disjoint set the
+whole-disc map needs (`crate::decrypt::AacsKeyMap::entry_for` requires
+disjoint ranges). Titles that share a clip resolve the SAME physical span
+(same LBAs -> same CPS unit -> same key). When a later range overlaps a kept
+one that carries the SAME key index and phase, the two are UNIONED (end
+extended to the max) — this covers both the exact-duplicate (shared clip)
+case and any partial overlap without ever dropping coverage, so no encrypted
+LBA is left in no range (which would pass through as ciphertext). A real disc
+never produces two DIFFERENT keys for one LBA; if that malformed case ever
+appeared, the later range is dropped to keep the set disjoint rather than
+extend one key over another key's LBAs.

docs/disc-profile.md

@@ -0,0 +1,9 @@
+# `disc::profile`
+
+Everything in `DiscProfile` is DERIVED from the `Disc` model at construction:
+the `Stream` enum is split into three typed vectors (audio/video/subtitle),
+the `qualifier` / `purpose` enums are decomposed into booleans, and the
+"default track" selection is precomputed so downstream never recomputes it.
+Every field is always populated — a sensible default (`"und"` language, empty
+`name`, `false` flag) stands in where the model has nothing, so consumers
+never handle a bare `Option`.

docs/disc-tests.md

@@ -0,0 +1,17 @@
+# disc_tests: capacity/layer derivation
+
+`scan_image_reports_capacity_in_bytes_and_the_layer_count` covers the scan
+reporting the medium's size on both axes it exposes, derived from the one
+sector count the caller hands in:
+
+* `capacity_bytes` is that sector count times the 2048-byte logical sector
+  (ECMA-167 / BD-ROM logical block size). It is what sizes a full-disc image
+  read and what the progress percentage divides by, so a wrong scale is a
+  wrong ISO length, not a cosmetic number.
+* `layers` distinguishes single- from dual-layer media. The threshold sits
+  between the two real capacities: a single-layer BD-25 is 12,219,392
+  sectors (25,025,314,816 bytes / 2048) and a dual-layer BD-50 is 24,438,784
+  sectors, so BD-25 must report 1 layer and BD-50 must report 2.
+
+`scan_image` takes the sector count as a parameter, so this exercises the
+real derivation without a 50 GB fixture.

docs/drive-access.md

@@ -29,7 +29,6 @@ seam).
 | `init()` | Route to the matching registered unlocker (if any), then prepare for reads |
 | `probe_disc()` | Probe disc surface for optimal speeds |
 | `read(lba, count, buf, recovery)` | Read sectors. Single-shot — no inline retries or reset. |
-| `reset()` | Eject-cycle escape hatch. Caller-invoked only; not on the read path. |
 | `lock_tray()` | Prevent tray ejection during rip |
 | `unlock_tray()` | Allow tray ejection (also runs on Drop) |
 | `eject()` | Eject disc tray |
@@ -104,14 +103,14 @@ descriptors or calls ioctls outside of a `ScsiTransport` implementation.
 
 | Platform | Implementation | Device |
 |----------|---------------|--------|
-| Linux | `SgIoTransport` — async `write`/`poll`/`read` on `/dev/sg*` | `/dev/sg*` |
+| Linux | `SgIoTransport` — synchronous `ioctl(fd, SG_IO, &hdr)` on `/dev/sg*` | `/dev/sg*` |
 | macOS | `MacScsiTransport` — IOKit SCSITask | IOKit service |
 
-The Linux backend uses the sg driver's asynchronous interface: `write()` submits
-the command, `poll()` waits with an enforceable wall-clock timeout, `read()`
-retrieves the result. If `poll()` times out, the fd is abandoned (closed in a
-background thread) and a fresh fd opened — the kernel's USB error recovery
-cannot block us. Opens with `O_RDWR | O_NONBLOCK`.
+The Linux backend issues each command as one synchronous `ioctl(fd, SG_IO, &hdr)`
+(`linux.rs`); the timeout is the kernel's, set via `hdr.timeout`, not a userspace
+`poll()`. Opens with `O_RDWR | O_NONBLOCK`. (Pre-0.13.20 this backend ran an async
+`write()` + `poll(1.5s)` + close-on-timeout + background-reopen pattern; it was
+reverted in 0.13.20 — see the note at the top of `linux.rs`.)
 
 The macOS backend uses a C shim (`macos_shim.c`) for IOKit exclusive access.
 The shim handles:
@@ -127,14 +126,13 @@ The shim handles:
 On non-zero SCSI status, the transport parses sense key from the sense buffer
 and returns `Error::ScsiError`.
 
-`SgIoTransport::reset` (Linux) does pure userspace state cleanup: an open +
-close pair to make the kernel cancel any SG_IO commands queued against a
-previous fd, a 2 s sleep to let the kernel finish that cancellation, then a
-fresh fd to send ALLOW MEDIUM REMOVAL to clear any stale tray lock. It does
-NOT issue `SG_SCSI_RESET` or escalate via STOP+START UNIT. Both were tried
-in 0.13.0–0.13.5 against the LG BU40N (Initio USB-SATA bridge); both failed
-to recover wedged drives and made the wedge worse. The macOS reset (which
-had been a no-op) was removed entirely in 0.13.6, and the top-level
+The Linux backend has no `reset`. `SG_SCSI_RESET` and STOP+START UNIT
+escalation were tried in 0.13.0–0.13.5 against the LG BU40N (Initio USB-SATA
+bridge); both failed to recover wedged drives and made the wedge worse, so no
+Linux transport-reset path exists today — recovery is just a fresh fd opened on
+the next command. The only `reset` on a transport in the crate is
+`SptiTransport::reset` on Windows (`windows.rs`). The macOS reset (which had
+been a no-op) was removed entirely in 0.13.6, and the top-level
 `scsi::reset()` / `reset_with_timeout()` / `reset_blocking()` wrappers were
 removed at the same time (no callers).
 
@@ -241,3 +239,13 @@ Available speeds:
 | Blu-ray | 1x (4,500 KB/s) through 12x (54,000 KB/s) |
 | DVD | 1x (1,385 KB/s) through 16x (22,160 KB/s) |
 | Max | 0xFFFF (drive decides) |
+
+---
+
+## Windows Path Normalization
+
+`normalize_path` in `src/drive/windows.rs` converts a device path ("D:",
+"D:\\", "\\.\D:", "\\.\CdRom0") to Windows `\\.\X:` form. A near-identical
+`normalize_device_path` exists in `scsi::windows`; both are kept because
+they live in separate `cfg(windows)` modules that cannot easily share a
+helper without introducing cross-module coupling.

docs/drive-linux.md

@@ -0,0 +1,15 @@
+# Linux `sg*` device enumeration
+
+`enumerate_sg_names` (in `src/drive/linux.rs`) lists `/dev/sgN` SCSI-generic
+device names to probe for optical drives.
+
+Linux assigns `/dev/sgN` sequentially across *all* SCSI-generic devices
+(disks, tape, HBAs, optical), not just optical drives. That means a fixed
+`sg0..15` range can miss an optical drive on a host with many other SCSI
+targets ahead of it in enumeration order.
+
+To avoid that, the function prefers the exact present-device list from
+`/sys/class/scsi_generic/`, which enumerates only the `sg*` nodes that
+actually exist. It falls back to a bounded `sg0..15` probe only when sysfs
+itself is unreadable, which happens in some minimal containers that lack a
+mounted `/sys`.

docs/drive-mod.md

@@ -0,0 +1,142 @@
+# src/drive/mod.rs — internal notes
+
+Long-form rationale relocated from `src/drive/mod.rs` comments that exceeded
+the comment-guard's internal-comment cap. Each section is pointed to by a
+short `// See docs/drive-mod.md — <topic>` comment at its original site.
+
+## Error-recovery mode page (PER bit)
+
+`MODE_PAGE_ERROR_RECOVERY` (0x01) is the SBC/MMC Read-Write Error Recovery
+mode page. We flip the `PER` bit to make the drive REPORT a recovered read
+(via CHECK CONDITION + sense key RECOVERED ERROR) instead of silently
+returning best-effort data as GOOD status. On marginal/dirty media that
+silent-GOOD data can be mis-corrected — a rip that "passed clean" but decoded
+with errors. With PER on, freemkv sees the marginal read and re-reads it in
+Pass N (a loud miss, never a silent commit). See
+`build_error_recovery_select_payload`.
+
+## `sleep_until_halted` — why it exists and why it was dormant
+
+This was `#[cfg(test)]` for two releases, kept alive only by its unit tests,
+while the two production paths that actually sleep — the `wait_ready` poll
+backoff (60 x 500 ms) and `spin_cycle`'s spin-down/settle pauses
+(`SPIN_DOWN_IDLE_SECS` + `SPIN_UP_SETTLE_SECS`) — used a plain
+`std::thread::sleep` and so were deaf to the operator's Stop for ~30 s and
+~15 s respectively. Every other drive path returns `Halted` at the next
+`checked_exec` boundary; a Stop pressed during spin-up simply did nothing
+visible until the poll ran out. The primitive existed; the sleeping code just
+did not call it. It is production code again.
+
+## `Drive::read` — single-shot contract and the removed inline retries
+
+`recovery=true` uses `crate::scsi::READ_RECOVERY_TIMEOUT_MS` (60 s, matches
+sg_dd) for the `freemkv_engine::recovery::patch` pass; `recovery=false` uses
+`crate::scsi::READ_TIMEOUT_MS` (10 s) for `freemkv_engine::recovery::copy`'s
+fast skip-forward sweep. Both budgets are generous enough that the drive can
+finish ECC recovery on a marginal sector — pre-0.13.21 this was 1.5 s on the
+fast path which forced the kernel mid-layer to time out and escalate while we
+waited anyway. On any failure this returns `Err(DiscRead)` immediately;
+orchestration (`freemkv_engine::recovery::patch` multi-pass, `DiscStream`
+adaptive batch halving) handles retry policy.
+
+Inline retry phases (5x gentle + reset+reopen + 5x more) were removed in
+0.13.6: on some USB-SATA bridges the inline reset wedged drive firmware
+without ever recovering a sector. The remaining recovery layers
+(`freemkv_engine::recovery::patch` multi-pass, `DiscStream` batch halving) do
+not touch the wedge-prone reset path.
+
+## `find_drive` — media-preference selection policy
+
+On a multi-drive system (common on Windows, where an empty/not-ready drive
+can enumerate first) returning the first drive blindly can pick a drive with
+no disc, dooming the operation. So `find_drive` opens each candidate in
+enumeration order, queries `Drive::drive_status` (GET EVENT STATUS, which
+works regardless of firmware state), and returns the first drive reporting
+`DriveStatus::DiscPresent`. If no drive reports a disc — or `drive_status()`
+is unavailable/returns `Unknown` everywhere (single-drive or quirky bridges)
+— it falls back to the first drive that opened, preserving historical
+behavior so those setups don't regress. For just listing drives without
+opening (e.g. UI sidebar), use `scsi::list_drives()` instead — it returns
+`DriveInfo` (path + identity) without the cost of running every drive's
+profile + identity probe.
+
+## `open_block_device_for_sg` — why no `O_DIRECT`
+
+Resolves a `/dev/sg*` path to the corresponding `/dev/sr*` block device by
+walking sysfs, then opens it for read. No `O_DIRECT`:
+`posix_fadvise(POSIX_FADV_DONTNEED)` flushes the cache before each pread,
+which avoids buffer-alignment requirements while still forcing fresh device
+reads. Returns `None` on any error (sysfs not present, no matching block
+device, open failed); callers treat that as "no fallback available" and
+propagate the original SCSI READ error.
+
+## `resolve_device` — staged, not yet wired
+
+The cross-platform dispatch is kept ready for the caller that will consume
+it, so the per-platform implementations below it (and their tests) stay
+live. `allow(dead_code)` marks that deliberately — this is not an accidental
+orphan.
+
+## Test rationale: recovery/halt/chunking coverage
+
+The `halt_tests` and `command_tests` modules exercise mutation-sensitive
+edges (halt-aware sleep timing, chunked-read offset arithmetic, drive-status
+byte decoding, spin-cycle/wait-ready halt responsiveness). The following
+notes preserve the "why this exact scenario" reasoning that the inline test
+doc comments were trimmed from:
+
+- **`disc_is_dvd_matches_only_dvd_profile_family`**: must match the DVD
+  profile family (0x0010..=0x001F) and ONLY that family. A false positive on
+  a BD/UHD profile (0x0040+) would skip the drive unlock UHD reads require; a
+  false negative on a DVD would re-introduce the CSS read failure. Widening
+  the range to `..=0x0040` makes the BD-ROM assert fire; a failed/short GET
+  CONFIGURATION must default to NOT-DVD so the unlock still runs.
+
+- **`media_event_reply` / media-status decoding**: MMC-6 §6.7 — byte 5 of the
+  GET EVENT STATUS reply is a Media Status only when the Event Header says a
+  media event descriptor follows (NEA clear AND Notification Class == 4).
+  Decoding byte 5 regardless of those preconditions reads a reserved/zero
+  byte as Media Status 0 and reports NoDisc on a drive that has a disc loaded
+  — the classic "works on my drive, not theirs" firmware split. The drive is
+  untrusted input, so an event-less reply must fall back to the TEST UNIT
+  READY status instead.
+
+- **Chunked-read tests** (`read_chunks_write_into_correctly_offset_buffer_regions`,
+  `an_undersized_buffer_errors_on_the_chunked_path_just_like_the_single_one`,
+  `chunk_lba_near_u32_max_errors_not_overflows`): the multi-chunk path slices
+  the caller's buffer by `count * 2048` and advances the per-chunk LBA with
+  `lba + done`, both unchecked. An undersized buffer PANICKED
+  ("range end index out of range") out of the public `read`/`read_fua`
+  instead of returning `Err(DiscRead)` like the single-chunk path; an LBA
+  range crossing `u32::MAX` overflowed (debug panic, or release wrap to a low
+  LBA silently read). These tests pin both to error-not-panic/overflow, and
+  one writes a distinct marker per chunk to confirm the byte-offset
+  arithmetic (`done * 2048`, not `done + 2048`) is correct — no other mock
+  touches the buffer contents, so a `*` -> `+`/`/` mutation would otherwise go
+  unasserted.
+
+- **`wait_ready`/`spin_cycle` halt tests**: `wait_ready` was the one drive
+  path that called `self.scsi.as_mut().execute(..)` instead of
+  `checked_exec`, and its 60 x 500 ms loop never read `self.halt` — a cancel
+  during spin-up was ignored for ~30 s. `spin_cycle` had the same gap across
+  two bare `execute` calls and two plain `std::thread::sleep` pauses
+  (`SPIN_DOWN_IDLE_SECS` + `SPIN_UP_SETTLE_SECS`), and it runs from the
+  recovery path — precisely when an operator is most likely to press Stop.
+  The tests pin: a Stop set before the call returns `Halted` immediately with
+  no command issued; a Stop set mid-poll (on a deterministic Nth call, no
+  wall-clock race) exits at the next `checked_exec` boundary; a Stop that
+  lands during the spin-down pause wakes the halt-aware sleep within
+  ~100 ms instead of blocking for the full 5 s.
+
+- **`read_logs_a_good_status_short_transfer`**: a READ(10) that completes
+  with GOOD status but a residual underrun is correctly refused, but the
+  refusal used to log nothing — so a drive that residual-underruns on GOOD
+  status produced the same silent journal as a scratched disc, and the
+  operator was sent after the wrong remedy (replace the drive vs. clean the
+  disc). The test pins that the refusal now warns with lba/transferred/
+  expected/code.
+
+## `open_block_device_for_sg` doc contract (kept short in code)
+
+See the section above for the `O_DIRECT` rationale; the pointer comment near
+the function keeps only the API contract.

docs/dropgate.md

@@ -0,0 +1,69 @@
+# `dropgate` — audio drop bookkeeping rationale
+
+## Keep/drop rule
+
+A clean mux keeps every frame it can and drops the ones it can't — video
+always survives (it's inter-frame predicted; a per-frame drop would cascade,
+so video resyncs/conceals instead), audio keeps every decodable access unit,
+and a damaged audio AU is dropped rather than shipped as a decoder-choking
+glitch.
+
+## Detection is per-codec
+
+The DETECTION is inherently per-codec — each format carries its own
+authoritative corruption check (DTS: the core sync/header parse per ETSI TS
+102 114; AC-3: the header CRC per ETSI TS 102 366; FLAC: the frame CRC-16;
+…). `DropTally` only carries the UNIFORM response so every audio parser
+behaves identically:
+
+1. **Count** kept vs dropped AUs and the dropped duration.
+2. **Log** every drop (fail-loud, never silent) — a per-drop trace plus a
+   once-per-track aggregate at `warn` so it surfaces without debug logging.
+3. **Whole-track fallback**: once a track is judged mostly undecodable, latch
+   a poison flag so the remainder is dropped too (a track that damaged isn't
+   worth muxing).
+
+## Sync preservation
+
+**Sync preservation is the caller's responsibility**, not this type's: the
+parser must advance its PTS clock across a dropped AU exactly as it would for
+an emitted one, so a drop becomes a silence gap and never a shift of the
+following audio. See `DtsParser`'s `stamp_pts` call ordering for the pattern.
+
+## `verified_dropped` vs `dropped`
+
+`verified_dropped` counts AUs dropped because they were INDIVIDUALLY verified
+undecodable (a failed CRC/header/parity check); only these feed the
+whole-track poison verdict. `dropped` also counts *collateral* drops — AUs
+discarded as a consequence of one corruption (TrueHD's resync-forward run, or
+a poisoned track) — which must NOT amplify a few real errors into a false
+whole-track loss.
+
+## `record_collateral_drop`
+
+A collateral drop is caused by another AU's corruption (TrueHD's
+resync-forward run to the next major sync, or an already-poisoned track), not
+by being individually verified undecodable. It is counted and logged for the
+drop report, but deliberately does NOT feed the poison verdict, so one
+corruption event can't amplify into a false whole-track loss.
+
+## `maybe_poison`
+
+Whole-track fallback: after enough AUs to judge, if more than half were
+dropped the track is too damaged to be worth muxing — latch `poisoned` and
+log it loudly once. The minimum-sample gate keeps a short damaged burst from
+poisoning an otherwise-good track. Judge on VERIFIED drops vs all AUs seen: a
+track is only poisoned when a majority of its access units are individually
+undecodable — not when a couple of corruption events forced long collateral
+resync runs.
+
+## Test: `interleaved_keeps_are_in_the_poison_denominator`
+
+The poison verdict is a RATIO — verified drops against every AU seen — so
+the kept count is half of it. `does_not_poison_a_mostly_good_track` records
+its keeps AFTER the single drop, and `maybe_poison` only runs inside
+`record_drop`, so the keeps are never in the denominator when the verdict is
+actually computed: that test passes even with the kept count never
+incremented. Interleaving them puts the kept count on the critical path,
+where losing it turns the ratio into "verified drops vs verified drops" —
+always >50% — and silently discards a healthy track.

docs/dts.md

@@ -0,0 +1,309 @@
+# DTS / DTS-HD elementary stream parser (`src/mux/codec/dts.rs`)
+
+Internal design notes moved out of source comments (see `ci/comment-guard.py`
+prose caps). Each section is pointed to by a short `//` comment at the
+corresponding site in `dts.rs`.
+
+## `DTS_HD_EXT_SYNC`
+
+An access unit is delimited by the next CORE sync; the parser locates and
+exactly sizes each extension substream (via `exss_frame_size`) so a false
+core sync inside the EXSS payload can't split the AU and truncate the
+lossless extension.
+
+## `emit_or_drop`
+
+Gates an assembled access unit through the decodability check and either
+pushes it or drops it. `au_pts`/`dur_ns` are already stamped on the shared
+PTS clock (which the caller advances whether or not the AU survives), so a
+drop leaves the following audio on its true timeline — a gap, not a shift.
+Every drop is logged (fail-loud, never silent).
+
+## `stamp_pts`
+
+`front` is the AU's own core-PES PTS (from `front_pts`); `dur_ns` its
+decoded duration.
+
+The model matches the (correct) AC-3 path: **re-base to each PES's own
+container timestamp, and advance by one frame duration ONLY within a run of
+AUs that share the same PES.** A new PES (its `front` differs from the
+previous AU's) trusts its own timestamp — so the emitted timeline tracks the
+container and never drifts. Advancing within a PES is what fixes the DVD
+case (several DTS core frames packed in one PES, which otherwise all
+collided on that single PES timestamp → "non monotonically increasing dts").
+A global running clock was WRONG here: once accumulated frame durations
+exceeded the PES spacing it never re-based, drifting the track minutes past
+the real length over a feature-long title.
+
+## `CORE_HEADER_MIN_BYTES`
+
+Number of leading bytes that must be buffered before the core `fsize` field
+(bytes 5-7) can be decoded. This is a HEADER-LAYOUT minimum — "enough bytes
+to read the size field" — and is deliberately distinct from
+`MIN_CORE_FRAME_BYTES` (the decoded-frame-size validity floor). They must
+not be conflated: this one gates buffer reads of the header, the other
+rejects implausible decoded sizes.
+
+## `MIN_CORE_FRAME_BYTES`
+
+Minimum plausible decoded DTS core frame size, per ETSI TS 102 114: the
+on-wire FSIZE floor is 95, so a real core frame is at least 96 bytes. A
+decoded `core_size` below this means we matched a false/corrupt core sync
+(a lucky 0x7FFE8001 in extension-substream payload whose 14-bit `fsize`
+decoded to a tiny value) rather than a real frame, so we resync instead of
+closing an access unit at a junk boundary and dropping the DTS-HD extension
+tail.
+
+## `PTS_UNSET`
+
+Sentinel for "no valid PTS base captured yet". Real PTS-in-ns values are
+non-negative (derived from the unsigned 90 kHz PES timestamp), so a
+negative value can never collide with a genuine timestamp. Used to mark the
+PTS base invalid after a forced flush so the next PES sets it regardless of
+buffer state.
+
+## `flush_tail`
+
+Emits the final buffered access unit (the last core + its extension
+substreams, which had no following core sync to close it during
+streaming), gated through the decodability check. Requires a complete core
+frame; drops a bare partial sync tail.
+
+## `SYNCWORD_BYTES`
+
+Byte length shared by the DTS core sync and the DTS-HD EXSS sync (both
+32-bit words). `next_core_boundary` finds the next *valid* core sync after
+the current core frame, to delimit the access unit: extension-substream
+payload can contain byte sequences that match the core syncword, so each
+candidate is validated by decoding its core size — a match whose decoded
+size is implausible (`< MIN_CORE_FRAME_BYTES` or `> MAX_AU_BYTES`) is a
+false sync and is skipped, continuing the search.
+
+## EXSS header field bit widths
+
+`EXSS_USER_DEFINED_BITS`, `EXSS_INDEX_BITS`, `EXSS_HEADER_SIZE_TYPE_BITS`,
+etc. are the DTS-HD extension-substream (EXSS) header field bit widths
+(ETSI TS 102 114, ExtSS header). `bHeaderSizeType` selects the short form
+(`nuExtSSHeaderSize` 8 bits, `nuExtSSFsize` 16 bits) or, for larger
+substreams, the long form (12 / 20 bits).
+
+## `exss_frame_size`
+
+DTS-HD extension substream (EXSS) total byte size — INCLUDING the
+`0x64582025` syncword — read precisely from its header. `buf` must begin
+with `DTS_HD_EXT_SYNC`. Returns `None` when the size fields aren't fully
+buffered.
+
+`nuExtSSFsize` is the total frame size in bytes minus one. Parsing it lets
+the AU framer skip the extension by its exact length instead of scanning
+its (arbitrary) payload for a core sync.
+
+## `next_core_boundary`
+
+Offset where the current access unit ends (the start of the next core
+frame). The AU is the core frame plus its trailing DTS-HD extension
+substreams, which are skipped PRECISELY by their declared size — so a
+chance core syncword inside the XLL lossless payload can never be mistaken
+for the next AU boundary (the bug that truncated the extension and produced
+the "Failed to decode block code(s)" class). Falls back to the heuristic
+core-sync scan only when an extension can't be sized (malformed / truncated
+input).
+
+## `scan_for_next_core`
+
+Heuristic fallback (the pre-fix behaviour): scan forward for the next core
+syncword whose decoded size is plausible. Used only when precise extension
+skipping can't proceed; a chance core syncword in extension payload usually
+decodes to an implausible size and is skipped.
+
+## `dts_core_frame_size`
+
+`fsize` is the 14-bit field at bits 46-59 of the header (bytes 5-7). On the
+wire `fsize` is the frame length minus one, so this returns `fsize + 1`,
+i.e. the core frame length in bytes (range 1..=16384). Callers treat the
+result as the actual byte length and the MIN..=MAX range checks assume so.
+
+Returns `0` when `data` is shorter than `CORE_HEADER_MIN_BYTES` — every call
+site rejects that via the minimum-frame lower bound, so a `0` is never
+mistaken for a valid tiny frame.
+
+## `dts_core_samples`
+
+Samples in one DTS core frame: `(NBLKS + 1) * 32`. `NBLKS` (7 bits) is the
+core-header PCM-sample-block count (ETSI TS 102 114) that fixes the frame's
+decoded sample count. Bit layout after the 32-bit sync: FTYPE(1) SHORT(5)
+CPF(1) **NBLKS(7)** FSIZE(14) …, so NBLKS = byte4 bit0 + byte5 bits7-2.
+
+## `DTS_PCMBLOCK_SAMPLES` / `DTS_SUBBAND_SAMPLES` (core-header validity)
+
+DTS core-header validity constants (ETSI TS 102 114). For a NORMAL frame
+`deficit_samples` must equal `DTS_PCMBLOCK_SAMPLES` — a termination frame
+may carry fewer; `npcmblocks` must be a multiple of `DTS_SUBBAND_SAMPLES`;
+`audio_mode` must be below `DTS_AMODE_COUNT`; `lfe_present ==
+DTS_LFE_FLAG_INVALID` is rejected.
+
+## `DTS_AMODE_COUNT`
+
+Number of LEGAL `AMODE` (channel-arrangement) codes. The 6-bit AMODE field
+(ETSI TS 102 114 §5.3.1) has 16 defined channel arrangements, codes 0-15;
+only 16-63 are reserved/user-defined and undecodable. The per-AMODE channel
+counts in ETSI TS 102 114 §5.3.1 cover all 16, confirming they are
+decodable — codes 10-15 are the 6/7/8-channel layouts. A frame is dropped
+only when `audio_mode >= DTS_AMODE_COUNT` (i.e. a truly reserved 16-63
+code); dropping a legal 10-15 multichannel core would silence recoverable
+audio.
+
+## `DTS_CORE_SR_VALID`
+
+Sample rate (Hz) per core `SFREQ` code (ETSI TS 102 114 Table 6-4); a `0`
+entry marks a reserved code that fails header validation as an invalid
+sample rate. Valid entries are locked to the spec by
+`dts_core_sfreq_table_matches_the_dca_spec`; the reserved codes are
+{0, 4, 5, 9, 10}.
+
+## `core_header_drop_reason`
+
+Decodability gate: the core-frame header validity checks from ETSI TS 102
+114. Returns `Some(reason)` when the DTS core-frame header is invalid — in
+which case the packet is undecodable ("Invalid data found") and dropping it
+loses nothing a decoder could have used. Returns `None` (keep) for a
+decodable header OR if the header can't be fully read (never false-drop on
+our own buffer underrun; the framer only emits AUs whose core is fully
+buffered and ≥ 96 bytes).
+
+The 4-byte core sync is already validated by the framer, so this reads the
+header fields that follow it. The 16-bit CPF header CRC is not verified (we
+skip past it) and the audio-header/side-info CRCs are likewise not checked,
+because decoders treat those bytes as optional/ignored — verifying them
+would drop frames that decode fine (false positives).
+
+## Test: `stamp_pts_reuses_front_when_no_running_cursor_yet`
+
+`stamp_pts`'s third arm (`else if front != PTS_UNSET`) is only reached once
+the first arm's `front != self.last_front_pts` has already failed (i.e.
+`front == self.last_front_pts`) and no within-PES running cursor is
+available yet (`next_pts_ns == PTS_UNSET`). In that state the AU must still
+be stamped with its own (repeated) front timestamp, not silently collapsed
+to 0 — a `!=` -> `==` typo on the guard would only take this arm when
+`front` IS the unset sentinel, producing 0 instead here and the sentinel
+value itself if front really were unset.
+
+## Test: `drain_front_collapses_offset_zero_markers_instead_of_leaking`
+
+Every drained access unit that shares its PES with the previous one pushes
+a new `(0, pts)` marker once rebased; `drain_front` must collapse those down
+to the single most-recent one each time, or `pts_marks` grows once per
+access unit for the life of the track — an unbounded allocation on a
+multi-hour disc. `front_pts()` alone can't observe this: it always finds the
+last offset-0 entry regardless of how many duplicates precede it, so the
+leak is invisible unless something checks that the collapse actually ran.
+
+## Test: `make_exss`
+
+Builds a real DTS-HD EXSS substream of `total` bytes (short header form),
+with an optional false DTS core syncword embedded in its payload (decoding
+to a plausible core size) — to prove precise sizing, not a payload scan,
+bounds the extension.
+
+## Test: `make_dts_ext`
+
+Builds a minimal DTS-HD extension substream of `size` bytes (just the sync
++ zero-padding). The parser delimits extensions by the next CORE sync, not
+by the extension's own size header, so a valid header isn't required — only
+that the bytes carry no spurious core sync.
+
+## Test: `bogus_tiny_core_sync`
+
+Builds 4 bytes that look like a DTS core sync but whose `fsize` field
+decodes to a tiny `core_size` (< MIN_CORE_FRAME_BYTES). With the dead-code
+guards this passed validation and could close an access unit at a junk
+boundary; with the fix it must be drained and resynced past.
+
+## Test: `next_core_boundary_exact_syncword_length_is_not_need_more`
+
+Only the 4-byte EXSS syncword is buffered after the core frame — no header
+fields at all. The guard `buf.len() < pos + SYNCWORD_BYTES` must be strict
+`<`: at exactly `pos + SYNCWORD_BYTES` the sync bytes ARE fully present, so
+the function proceeds to identify them as an extension sync (then fails to
+size the header and falls back, ending in `NextCore::None` here since
+nothing after it looks like a core sync either). A `<=` typo would instead
+return `NeedMore` at this exact length without ever inspecting what the 4
+buffered bytes are.
+
+## Test: `make_bad_dts_core`
+
+Builds a structurally-framed but UNDECODABLE core: a valid `make_dts_core`
+whose LFE flag is set to the reserved value 3 (`DTS_LFE_FLAG_INVALID`). It
+still sizes and syncs correctly (so the framer delimits it normally), but
+the core-frame header validity check rejects it as an invalid LFE flag
+(ETSI TS 102 114 §5.3.1: an LFF value of 3 is invalid). LFE is byte10
+bits2-1, and does NOT feed the frame duration (NBLKS + SFREQ only), so a
+dropped bad core still carries the same `DTS_CORE_DUR_NS` as its good peers.
+
+## Test: `reparse_real_dts_file`
+
+Real-data fixture (ignored). Re-parses a raw `.dts` elementary stream
+through `DtsParser` and writes the emitted access units back out, so the
+garbage-extension → core-only drop can be validated against an actual
+damaged stream (e.g. an extracted DTS-HD MA track) end-to-end with an
+external DTS decoder. Env: `DTS_IN` (input), `DTS_OUT` (output).
+
+    cargo test --lib dts::tests::reparse_real_dts_file -- --ignored --nocapture
+
+## Test: `find_sync_matches_a_buffer_that_is_exactly_the_syncword`
+
+`find_sync` scans `0..=len-4`, so a buffer that is EXACTLY the syncword
+still matches. The existing tests cover 0, 3 and "longer than 4", which
+leaves the `len == 4` boundary open — and that is the case a syncword split
+across PES packets lands on the moment its last byte arrives.
+
+## Test: `a_core_header_of_exactly_the_minimum_length_is_decoded_not_deferred`
+
+`CORE_HEADER_MIN_BYTES` is "enough bytes to DECODE the size field", so a
+buffer holding exactly that many must be decoded, not deferred. The
+distinction is visible precisely at the boundary: with 10 bytes of a core
+sync whose decoded size is sub-spec, the parser must recognise the false
+sync, drain past it and resync down to the 3-byte carry-over tail. Waiting
+instead leaves the false sync sitting at the front of the buffer, where it
+blocks every later real core behind it.
+
+## Test: `flush_emits_a_core_that_exactly_fills_the_buffer`
+
+The end-of-stream flush must emit a final access unit whose core is exactly
+as long as the buffer — the ordinary case, since the last AU is closed by
+end-of-stream rather than by a following core sync. Rejecting it at the
+boundary silently drops the last frame of every DTS track.
+
+## Test: `flush_discards_a_long_buffer_that_does_not_begin_with_a_core_sync`
+
+The flush guard is a DISJUNCTION: a buffer that does not BEGIN with a core
+sync is discarded whatever its length. Requiring both conditions instead
+lets a long run of junk through to `dts_core_frame_size`, which happily
+decodes a 14-bit size out of arbitrary bytes — and the flush then emits an
+"access unit" that is not DTS at all.
+
+The junk here is sized so that mis-decoding it yields a plausible core size
+that the buffer fully covers, which is exactly when the wrong answer looks
+like a right one.
+
+## Test: `exss_frame_size_needs_the_worst_case_header_and_no_more`
+
+`EXSS_HEADER_MIN_BYTES` is the WORST-CASE header length — the long form's
+43 bits after the syncword, rounded up to 6 bytes, plus the 4-byte sync. It
+gates whether an extension substream can be sized precisely, and that is
+what keeps a chance core syncword inside XLL payload from being mistaken
+for the next AU boundary; too large and every extension falls back to the
+payload scan, too small and the reader runs off a truncated header.
+
+Pinned at both sides of the boundary rather than by value, so the field
+widths it is summed from stay honest.
+
+## Test: `an_access_unit_carries_the_source_of_the_packet_its_core_arrived_in`
+
+The whole point of the shared buffer: an access unit whose core arrived in
+an EARLIER packet keeps that packet's source offset, not the offset of
+whichever packet completed it. At a clip boundary the two belong to
+different clips, and taking the later one puts the unit in the wrong clip —
+which is what left nine audio and subtitle tracks unplaceable.
+</content>
+</invoke>

docs/dvd-audio-probe.md

@@ -0,0 +1,149 @@
+# DVD AC-3 physical sub-stream probing
+
+## Why this exists (a real-disc wrong-substream bug)
+
+A DVD VTS IFO declares its audio streams in a fixed table, and freemkv's
+scan assigns each declared stream a `private_stream_1` sub-stream id purely
+by per-codec ordinal — the first AC-3 stream becomes `0x80`, the second
+`0x81`, and so on (`ifo::assign_audio_sub_stream_ids`). That assumes the
+physical sub-stream order on the wire matches the IFO declaration order.
+
+On some discs it does NOT. A real R2 PAL DVD release's feature declares
+ONE AC-3 audio stream the IFO nibble marks as 5.1 (6 channels), but the
+physical VOB carries the 5.1 main mix and a 2.0 down-mix on DIFFERENT
+`0x8x` sub-stream ids, and the 2.0 is the one that happens to land at the
+ordinal `0x80` slot. Routing the declared 5.1 stream to `0x80` by ordinal
+therefore muxes the 2.0 down-mix while labelling it 5.1 — the wrong
+physical track.
+
+The robust fix is data-driven and codec/disc agnostic: read each physical
+AC-3 sub-stream's REAL channel count from the VOB (the `acmod`/`lfeon` of
+its first frame after the `0x0B77` sync) and route each IFO-declared AC-3
+stream to the physical sub-stream whose actual channel count matches the
+IFO's declared count — instead of trusting the ordinal. This never
+re-reads the disc beyond a bounded head-of-feature probe and degrades to
+the original ordinal mapping when the probe yields nothing
+(unreadable/short VOB).
+
+## `PROBE_SECTORS` sizing
+
+How many 2048-byte sectors of the first feature extent to probe. The head
+of a DVD feature opens with logos/warnings whose audio is frequently a
+thin 2.0 bed on the FIRST sub-stream only — the other physical `0x8x`
+sub-streams and the main 5.1 mix do not appear until a sector or two
+further in. 512 sectors (1 MiB) was too short: on one real disc it saw
+ONLY `0x80`, and only its opening 2.0 frames. 1024 sectors (2 MiB)
+reliably contains at least one frame of every physical AC-3 sub-stream
+AND enough of `0x80` to reach its 5.1 frames. Still bounded so a live
+drive is never hammered (see the project "don't hammer the live drive"
+rule).
+
+## Why the maximum channel count, not the first frame
+
+The first frame of a sub-stream at the head of a feature is NOT
+representative. A DVD opens with logos/warnings, and the main `0x80`
+sub-stream there frequently carries a thin 2.0 bed before transitioning
+to its real 5.1 main mix a fraction of a second later (observed on a real
+disc: `0x80`'s first frames are acmod=2 → 2 channels, then it becomes
+acmod=7+lfe → 6 channels within the same 2 MiB window). Recording only
+the FIRST frame read `0x80=2` and missed the 5.1 entirely, defeating the
+channel-match routing. The 5.1 capability of a sub-stream is the
+*maximum* channel count any of its frames carries, so
+`probe_ac3_substream_channels` scans them all and keeps the max.
+
+## `remap_audio_pids` conservatism
+
+Conservative — it only ever REASSIGNS among the physical sub-streams the
+probe actually saw, and only when a better (exact-channel) match exists
+than the stream's current assignment. A stream whose current sub-stream
+already matches is left alone; a stream with no matching physical
+sub-stream keeps its ordinal assignment. So a normal disc (physical order
+== IFO order) is a no-op.
+
+## Test helper notes (`dvd_audio_probe::tests`)
+
+- `ac3_frame`: builds a single, correctly-SIZED AC-3 frame whose
+  `acmod`/`lfeon` encode a known channel count. `byte4` is
+  `fscod=0 | frmsizecod=0`, so `ac3_frame_size` reports 128 bytes and the
+  frame is zero-padded to exactly that — this lets `max_substream_channels`
+  advance frame-by-frame over a multi-frame payload exactly as it does on
+  real VOB data. The BSI bits are laid down with a writer so the test
+  never hand-miscomputes the lfeon offset, matching `acmod_channels`'
+  reader.
+- `ps_ac3_frames`: builds a minimal `private_stream_1` PES carrying
+  `frames` for `sub_id`, each preceded only by the 4-byte AC-3 sub-header
+  at the PES head. Mirrors the on-disc layout the PS demux expects: PES
+  start `0x000001BD`, length, PES header (no PTS), sub-header
+  `[sub_id, frame_count, ptr_hi, ptr_lo]`, then the concatenated AC-3
+  frames.
+
+### `probe_reads_max_channels_no_cross_contamination`
+
+Real-disc regression — the probe must read each sub-stream's TRUE
+(max-mix) channel count, not be poisoned by an unrepresentative head
+frame, and must NOT cross-contaminate between sub-streams. Mirrors the
+real on-disc layout that caused the mis-read: the feature head carries
+`0x80` opening with a 2.0 frame and THEN a 5.1 frame (its real main mix),
+interleaved with `0x81` carrying only 2.0. The old first-frame probe read
+`0x80=2` (the logo bed) and missed the 5.1; the max-over-frames probe
+must report `0x80=6` and `0x81=2`.
+
+### `max_substream_channels_locates_sync_after_leading_non_sync_bytes`
+
+Regression guard for a hand-checked mutation (`+` → `-` at the
+`pos + rel` offset computation): with `pos` starting at 0 and the first
+sync found 3 bytes in, `pos - rel` would underflow a `usize` and panic,
+or (if it somehow didn't) index the wrong start entirely. `pos + rel` is
+the only computation that is always in-bounds, since `rel` is itself
+bounded by the length of the slice searched from `pos`.
+
+### Unmappable-size fallback tests
+
+When an AC-3 header's `fscod`/`frmsizecod` is unmappable (reserved
+`fscod == 3`), `max_substream_channels` must fall back to stepping
+`start + 2` bytes past the sync to re-lock onto the next genuine sync,
+and must keep making forward progress doing so (never revisit the same
+sync, which would loop forever, and never jump so far that it skips the
+very next real frame).
+
+- `max_substream_channels_unmappable_size_steps_forward_by_two` lays a
+  bogus-sized header at absolute offset 4 (so `start == 4`,
+  `start + 2 == 6`) immediately followed, at offset 6, by a real, fully
+  decodable 2.0 frame — the position the `+ 2` fallback must land on
+  exactly.
+- `max_substream_channels_unmappable_size_at_start_steps_forward_not_back`
+  puts the unmappable-size sync at absolute offset 0 (`start == 0`) so
+  that stepping backward instead of forward (`start - 2`) would underflow
+  rather than merely land on the wrong byte. Also proves the real frame is
+  still found 6 bytes further in, confirming forward progress past the
+  bogus header.
+
+### `remap_reads_current_substream_via_and_not_or_or_xor`
+
+`remap_audio_pids` must read a stream's CURRENT physical sub-stream id
+from the low byte of its PID via `pid & 0x00FF` — not `|` or `^` with
+`0x00FF`, both of which force the low byte to `0xFF` regardless of the
+real PID and so always miss the "already matches" shortcut. That matters
+observably when TWO physical sub-streams share the same probed channel
+count: with a correct read, a stream already sitting on a matching
+sub-stream is left alone (conservative, per the module's documented
+behaviour); with the low byte forced to `0xFF`, `probed.get(&0xFF)` is
+always `None`, so the code falls through to the "find any unclaimed
+match" path and picks the FIRST (lowest-keyed, BTreeMap-ordered) matching
+physical sub-stream instead — which here is a *different* sub-stream
+(0x80) than the one the PID already correctly names (0x81), producing a
+spurious PID change.
+
+### `probe_and_remap_reroutes_swapped_substream_scenario_end_to_end`
+
+End-to-end `probe_and_remap`: a real-disc-shaped MpegPs title (one
+declared 5.1 AC-3 stream ordinally assigned 0x80) whose physical VOB
+bytes carry the 2.0 down-mix on 0x80 and the real 5.1 on 0x81. This must
+reach the `remap_audio_pids` call and re-route the stream to 0xBD81. It
+also, by construction, proves each of the guards along the way lets a
+real, positive case through: the content-format check must NOT bail on
+`MpegPs` (only on non-`MpegPs`), the AC-3 presence check must NOT bail
+when AC-3 IS present, and the sector-count check must NOT bail when the
+count is nonzero — any one of those inverted would skip the probe
+entirely and leave the PID at its untouched ordinal value (0xBD80), which
+the test's assertion would catch.

docs/dvd.md

@@ -0,0 +1,177 @@
+# DVD Title Scan (src/disc/dvd.rs) — Internal Notes
+
+Rationale, regression history, and test-fixture layout notes that were
+originally inline comments/doc-comments on private items in
+`src/disc/dvd.rs`, relocated here to satisfy the comment-guard's internal-
+comment cap. Each pointed-to site in the source carries a short `// See
+docs/dvd.md — <topic>` line.
+
+## `Disc::scan_dvd_titles` halt handling
+
+Cancellation: `halt` is polled before the IFO tree is read, and an IFO read
+that fails with `Error::Halted` — how a live drive reports a Stop, since
+`Drive::checked_exec` fails every command once its flag is set — is
+propagated rather than swallowed. Every other IFO failure keeps its
+best-effort `Ok(vec![])`.
+
+It has to be an error and not an empty title list, for the same reason
+spelled out on `Disc::scan_hddvd_titles`: a cancelled enumeration that
+returned `Ok` would be indistinguishable from a disc that genuinely holds
+fewer titles. This one was the worst of the three enumerators — a bare
+`Err(_) => return Vec::new()` turned an operator Stop into ZERO titles at
+rc=0, a disc reported as carrying no video at all.
+
+`scan_dvd_titles` returns the scanned titles plus, when the disc's own
+First-Play navigation deterministically dispatches to a title, that title's
+`playlist_id` — the nav-resolved main feature. The caller feeds it into
+`sort_titles_by_main_feature` as the DVD `nav_feature`, the same seam the BD
+path uses. It is `None` (existing ranking heuristics stand) whenever the
+navigation is menu-only, malformed, or does not converge.
+
+## DefaultDuration / cadence TODO
+
+`measured_cicp` TODO(spec): populate `top_field_first` + measured colour
+from `Mpeg2Parser` once tracks are built after frame parsing — needs a
+`CodecParser`->title channel like `codec_private`. Until wired, `None`
+falls back to TFF / PAL-NTSC guess.
+
+DefaultDuration TODO(spec): comes from IFO `frame_rate`, so a
+soft-telecined 23.976-in-29.97 DVD reports 29.97 instead of true film
+rate. Cadence is detectable via `nb_fields` (2:3 pulldown); needs the same
+channel as `top_field_first` above.
+
+## Test fixture builders: `build_vmg` / `build_vts`
+
+`build_vmg` builds a VIDEO_TS.IFO: magic "DVDVIDEO-VMG"@0, TT_SRPT sector
+ptr@0xC4. TT_SRPT lives at `tt_srpt_sector*2048`: `num_titles(u16)`@0, then
+12-byte entries from +8. Each entry: `num_chapters(u16)`@+2, `vts_number`@+6,
+`vts_title_num`@+7.
+
+`build_vts` builds a VTS_XX_0.IFO. Layout per ifo.rs:
+- magic "DVDVIDEO-VTS"@0
+- `vtstt_vobs` (Title VOBS start sector, u32 BE)@0xC4 — the production
+  `vob_start_sector` the cell sectors are relative to. (0xC0 is
+  `vtsm_vobs`, the menu VOBS, which the scan must NOT use.)
+- VTS_PGCIT sector ptr(u32 BE)@0xCC
+- video attr byte@0x200
+- `num_audio(u16 BE)`@0x202, audio blocks (8B) @0x204
+- `num_subs(u16 BE)`@0x254, subtitle blocks (6B) @0x256
+
+PGCIT (at `pgcit_sector*2048`): `num_pgcs(u16)`@0, PGC info entries (8B)
+from +8 with PGC byte offset(u32 BE)@+4. PGC: `nr_programs`@0x02,
+`nr_cells`@0x03, BCD time@0x04, `pgm_map` ptr@0xE6, `cell_playback` ptr@0xE8
+(both u16 BE rel to PGC start).
+
+## `HaltingReader` test double
+
+A `SectorSource` that fails every read at or above `halt_at` with
+`Error::Halted` — how a LIVE DRIVE behaves once the operator presses Stop:
+`Drive::checked_exec` fails every SCSI command with `Halted` from then on,
+and `Drive::read` deliberately preserves the variant. Reads below the
+threshold still succeed, so the scan gets far enough to have something to
+truncate.
+
+## Test: `halted_ifo_read_is_not_reported_as_a_shorter_disc`
+
+A Stop on a LIVE DRIVE never touches `ScanOptions::halt`: `Drive` has its
+own flag and `checked_exec` fails every SCSI command with `Error::Halted`
+once it is set. The DVD enumerator must not swallow that into a
+successful scan.
+
+This was the worst of the three enumerators. RED BEFORE GREEN, two
+distinct swallows, both measured with the fix reverted:
+- `ifo::parse_vmg` treats a failed title set as a placeholder entry and
+  continues, so a cancel landing on VTS_02's IFO returned
+  `Ok([VTS_01_1.VOB])` — one title from a two-title disc.
+- `scan_dvd_titles`'s `Err(_) => return Vec::new()` turned a cancel landing
+  on VIDEO_TS.IFO itself into ZERO titles at rc=0 — a disc reported as
+  holding no video at all.
+
+Both are indistinguishable from a real disc, and both are now
+`Err(Error::Halted)`.
+
+Fixture: two title sets, VTS_01's IFO at `PART_START+6000`, VTS_02's at
+`PART_START+7000`. Both ICBs sit far below, so filesystem metadata
+resolves fine and only the second title set's CONTENT read is cancelled —
+the truncation case.
+
+## Test: `scan_dvd_titles_uses_title_vobs_not_menu_vobs`
+
+Regression (first-play menu prepended to the feature): `vob_start` must
+come from the **Title** VOBS pointer `vtstt_vobs` (VTS_IFO 0xC4), NOT the
+**menu** VOBS pointer `vtsm_vobs` (0xC0). On discs with a per-title menu —
+e.g. the Universal "the parental level has been set, press yes" first-play
+still — `vtsm_vobs` points at that menu VOB, which sits just before the
+title VOB. Cell `first_sector` values are relative to `vtstt_vobs`; reading
+0xC0 prepended the menu and shifted every extent back by
+`vtstt_vobs - vtsm_vobs`, so the rip opened on the parental prompt instead
+of the movie (one real NTSC R1 disc: vtsm=44, vtstt=3640).
+
+Here `build_vts` stamps `vtstt_vobs = 3640` (0xC4); the test additionally
+stamps a *different* `vtsm_vobs = 44` (0xC0). The extent must resolve
+from 3640.
+
+## Test: `scan_dvd_titles_extent_is_absolute_three_term_sum`
+
+ABSOLUTE-REBASE regression (real-disc menu-at-start fix): `ifo::parse_vts`
+now sets `vob_start_sector = file_start_lba(IFO) + vtstt_vobs`, so an
+extent's `start_lba` must equal the sum of THREE independent terms — the
+IFO file's absolute on-disc LBA, the IFO-relative `vtstt_vobs` (0xC4), and
+the cell's `first_sector` — none of which may be dropped. The earlier code
+used the bare relative `vtstt_vobs`, placing every extent `ifo_lba`
+sectors too early (the rip opened in the VMGI/menu region before drifting
+into the movie). The other tests fold two of the three terms together
+(zero cell offset, or a single combined expectation); this one keeps all
+three distinct and non-overlapping so a regression to ANY two-term
+combination is caught.
+
+## Test: `scan_dvd_titles_lpcm_routes_to_a0_pid_range`
+
+LPCM SCAN ROUTING (audit §2 / §5 #6): the 0xA0..=0xA7 PID range was never
+exercised in the dvd.rs scan. An LPCM stream (coding_mode 4) at audio
+position 1 must get `sub_stream_id 0xA1` → PID `0xBDA1` via
+`dvd_audio_pid`, distinct from the AC-3 `0xBD80` space, with its real
+channel count preserved.
+
+## Test: `scan_dvd_titles_multiple_vobsub_tracks_distinct_pids`
+
+MULTI-VOBSUB SCAN (audit §2 / §5 #6): the single-subtitle test covered one
+track; a multi-subtitle VTS must emit one `Stream::Subtitle` per entry
+with distinct PIDs (`0x20 + ordinal`) and per-language tags, all sharing
+the PGC palette `codec_data`.
+
+## `stamp_first_play_jumptt` test helper
+
+Stamp a First-Play PGC into a VMG whose pre-command list is a single
+unconditional `JumpTT ttn`, so `dvdnav::resolve_main_title` resolves that
+title through TT_SRPT. Placed in sector 0, clear of the magic / FP_PGC /
+TT_SRPT pointers `build_vmg` already writes.
+
+## Test: `scan_dvd_titles_nav_promotes_first_play_target`
+
+The DVD First-Play nav promotion branch (issue #40): when
+`resolve_main_title` returns a `(vtsn, vts_ttn)` target, `scan_dvd_titles`
+must map it — via the 1-based `vts_ttn == vts_title_idx + 1` join within
+the matching `vts_number` — to the running `title_number`, and surface it
+as the `nav_feature`. TT_SRPT here maps title 2 → (VTS 2, title-in-set 1);
+the First-Play unconditionally `JumpTT 2`, so the promoted feature must be
+the SECOND scanned title (VTS_02 → title_number 2). An off-by-one on the
+join or a `vtsn`/`vts_ttn` field swap would promote the wrong title or
+none.
+
+## Test: `scan_dvd_titles_drops_leading_scene_index_cell`
+
+End-to-end bug-4 fix: a feature PGC that opens with a leading interleaved-
+angle sub-block cell (category 0x90 = in-block cell of an angle block)
+must have that cell DROPPED from the muxed extents, so the rip starts at
+the real feature. Chapters shift earlier by the dropped duration.
+
+## Test: `scan_dvd_titles_mp2_audio_pid_fallback_is_additive`
+
+Audio PID fallback (dvd.rs `Disc::scan_dvd_titles`): when an audio stream
+has no on-wire private_stream_1 sub-stream id — MP1/MP2 audio, per
+`ifo::assign_audio_sub_stream_ids` — the PID falls back to `0xBD00 + i`
+where `i` is the stream's positional index in the IFO audio-attribute
+table. Two MPEG-audio (coding_mode 2) streams must land on two DISTINCT,
+correctly-offset PIDs: 0xBD00 and 0xBD01. This pins the `+` (not `-`/`*`)
+so the second stream doesn't collide with, or wrap under, the first.

docs/dvdnav-mod.md

@@ -0,0 +1,23 @@
+# src/dvdnav/mod.rs
+
+## Module rationale
+
+Byte layout follows the DVD-Video specification (VMGI/VTSI headers,
+PGC/cell tables, PCI/HLI button packets); the VM command decoder is
+verified against real discs.
+
+Current contents: `vmcmd` — the VM command decoder; `nav` — the
+First-Play navigation executor that resolves which title the disc's own
+navigation selects as the feature.
+
+## `resolve_feature_start` — parked status (issue #40)
+
+PARKED (issue #40, `USE_NAV_RESOLVER=false`): this is intentionally a stub,
+not an accidental dead one. It unconditionally returns `None` and ignores
+`reader`/`udf` on purpose — the IFO/PCI parsing + nav executor (built on
+`vmcmd`) land incrementally behind that flag. Until wired in, calling this
+is behaviour-neutral (the caller always falls back); improvements to the
+resolver take effect here without touching the call site. Do not delete.
+
+`reader`/`udf` are the seam inputs the nav executor will consume to read
+VIDEO_TS.IFO + the VTS IFOs/menu VOBs. Reserved until that lands.

docs/dvdsub-mod.md

@@ -0,0 +1,28 @@
+# dvdsub — VobSub SPU boundary rule
+
+The presence of a PTS — not merely an open `pending` — is the authoritative
+SPU-boundary signal, so a lost continuation or a corrupt SPU_size can't merge
+the next subtitle into the stuck unit.
+
+## ycbcr_to_rgb range convention (deliberate)
+
+This uses the **full-range (JFIF) BT.601** coefficients with no 16/235 luma
+scaling. DVD IFO palette YCbCr is nominally studio-swing BT.601, so
+studio-swing math would be more colorimetrically "correct" in isolation. But
+the output here is a VobSub `.idx` `palette:` line, and the entire VobSub
+ecosystem (the original tooling, mkvtoolnix, players that read the `.idx`
+palette) is built around this full-range formula — it is the de-facto
+on-disk convention. Emitting studio-swing-scaled RGB here would make
+freemkv's palettes inconsistent with every other tool and wrong in players
+that assume the VobSub convention. Do NOT "fix" this to studio-swing without
+changing the consuming side in lockstep.
+
+## ycbcr_to_rgb_reads_byte2_as_cr_and_byte3_as_cb test fixture
+
+A saturated RED entry appears on disc as Y=76, Cr=255, Cb=85 (full-range
+BT.601 encoding of RGB #FF0000), i.e. bytes `[0x00, 76, 255, 85]`. Reading
+byte 2 as Cb and byte 3 as Cr instead turns this entry BLUE, which is the
+exact user-visible symptom. The fixture is deliberately NOT built from this
+crate's own doc comments: those described the order wrongly for a long time,
+and the previous version of this test inherited the error from them and
+therefore could not detect it.

docs/ebml.md

@@ -0,0 +1,62 @@
+# src/mux/ebml.rs
+
+## `fixed_width_vint8`
+
+Encodes `data_size` as the FIXED-WIDTH 8-octet EBML VINT used to back-patch
+a master element's size field: the `0x01` VINT_MARKER octet followed by the
+56-bit VINT_DATA payload, big-endian (RFC 8794 section 4.4 — an 8-octet
+VINT carries 7 octets of VINT_DATA).
+
+Extracted so the full 56-bit payload can be exercised directly: reaching
+the high payload bytes through `end_master` / `end_master_buf` would take
+a multi-terabyte buffer, leaving them unconstrained by any test.
+
+`data_size` must be below 2^56; both callers check that first.
+
+## `start_master_buf` / `end_master_buf`
+
+This is the seek-free twin of `start_master`/`end_master` for elements
+small enough to assemble whole before hitting the file (a BlockGroup: one
+Block plus a couple of tiny elements). Because `end_master` always
+back-patches a FIXED-WIDTH 8-byte VINT (`0x01` + 7 payload bytes) rather
+than a minimal-width one, the bytes produced by this pair are byte-for-byte
+identical to the seek-and-back-patch pair — assembling in memory cannot
+change the emitted Matroska.
+
+## `read_exact_bounded`
+
+Reads exactly `len` bytes WITHOUT trusting `len` to size the allocation.
+
+`vec![0u8; len]` on an attacker-controlled EBML size would allocate
+gigabytes before the read fails. Instead the reader is capped to `len`
+and the buffer grows as bytes actually arrive: a malformed element that
+claims a huge length but supplies few bytes allocates only what it
+delivers, then errors on the short read.
+
+## Test: `buffered_master_matches_seeking_master_byte_for_byte`
+
+The buffer-based master helpers must produce byte-for-byte what the
+seek-based ones produce. `write_block_group` was rewritten onto
+`start_master_buf`/`end_master_buf` to eliminate ~4 seeks (and 4 MiB
+BufWriter flushes) PER FRAME, which on an MPEG-2 title is ~350k frames — a
+change only safe because the two encodings are identical.
+
+Both write a FIXED-width 8-byte VINT placeholder (0x01 + 7 payload bytes)
+and patch it in place; neither ever emits a minimal-width size. This test
+pins that, so a future "optimisation" of either one to minimal-width sizes
+cannot silently desync the two and change emitted Matroska.
+
+## Test: `buffered_master_nests_correctly`
+
+Nested masters must patch correctly too — the MVC BlockGroup nests
+BlockAdditions > BlockMore inside the BlockGroup, and in-memory patching
+works by index rather than by file offset, so nesting is where an
+index-arithmetic slip would show up.
+
+## Test: `fixed_width_vint8_is_big_endian_over_the_full_payload`
+
+The fixed-width 8-octet VINT is `0x01` followed by the 56-bit VINT_DATA
+payload in BIG-ENDIAN order (RFC 8794 section 4.4). Every payload octet is
+distinct here, so a shifted, reversed or dropped octet is visible; the top
+payload octets are unreachable through `end_master` without a
+multi-terabyte buffer, which is why this is tested at the encoder.

docs/encode.md

@@ -0,0 +1,51 @@
+# `dirimage::encode` — descriptor encoder notes
+
+Overflow rationale for comments in `src/dirimage/encode.rs` that would
+otherwise exceed the comment-guard caps. Each section below is pointed to
+by a short `//` comment at the relevant spot in the code.
+
+## Why a pure function
+
+`encode` is a pure function from `Layout` to sectors — nothing here touches
+the filesystem. That is what makes it testable against the production
+parser in `udf.rs`: the same bytes this module writes are read back and
+checked by the real UDF reader, so the encoder and the parser can't drift
+apart silently.
+
+## Why UDF 1.02 with a single Type-1 partition map
+
+UDF revision 1.02 with a single Type-1 partition map is deliberate: it is
+the DVD-Video profile, it is the shape `read_filesystem` takes when
+`num_partition_maps < 2`, and it avoids the UDF 2.50 Metadata Partition
+entirely. That also means a synthetic image never exercises the Metadata
+Partition path in `udf.rs` (`:946-991`).
+
+## `finish_tag`: why `tag_loc` correctness matters
+
+Getting `tag_loc` wrong (absolute vs. partition-relative) is the classic
+reason a hand-built volume mounts nowhere: a driver that validates the tag
+location rejects the descriptor outright. `desc_len` is the descriptor's
+total length including the tag; the CRC covers `buf[16..desc_len]`.
+
+## `encode_cs0`: why ASCII, not Latin-1, for the 8-bit form
+
+`parse_udf_name` (`udf.rs:1467`) decodes a compression-8 name with
+`from_utf8_lossy`, so a 0x80-0xFF byte — legal CS0 under Latin-1 — would
+come back as U+FFFD. Every character above 0x7F therefore takes the 16-bit
+(UTF-16BE) form, which that parser decodes correctly.
+
+## `file_entry`: why tag 261, not the Extended File Entry (266)
+
+Real BD-ROMs use the Extended File Entry (tag 266), but an EFE requires
+UDF 2.00+, and this image declares 1.02, so `file_entry` writes the plain
+File Entry (tag 261) instead. `udf.rs` reads both — the 261 field offsets
+it uses (`l_ea` 168, `l_ad` 172, ADs at `176 + l_ea`) are the ones written
+here.
+
+## `push_fid`: why FIDs may span logical blocks
+
+FIDs are packed with no inter-descriptor padding beyond the 4-byte
+alignment the spec mandates, and they are allowed to span logical blocks —
+which is also what `read_directory` (`udf.rs:1312`) assumes: it walks the
+directory extent as one flat byte run and stops at the first non-257 tag,
+so any block-alignment gap would truncate the directory.

docs/encrypt.md

@@ -0,0 +1,151 @@
+# encrypt.rs — relocated rationale
+
+Overflow prose that would not fit under `ci/comment-guard.py`'s caps,
+moved here per file with a `// See docs/encrypt.md — <topic>` pointer
+left at the original site.
+
+## HandshakeResult::drive_unlocked
+
+True when the VID came from an unlocker (in `freemkv-unlock`) that
+unlocked the drive. Such a drive serves CLEAR content, so AACS bus
+encryption is already removed AT THE DRIVE — the same end state a
+successful cert handshake's `read_data_key` provides, just via
+firmware instead of the AKE. The bus-key gate MUST credit this as a
+valid bus-removal: bus encryption is unremovable only when NEITHER the
+firmware unlocked the drive NOR the cert handshake yielded a bus key.
+Without this, a SUCCESSFUL unlock (VID present, `read_data_key: None`)
+paradoxically trips the gate and blocks ALL key resolution (incl. the
+online source).
+
+## bus_encryption_removed
+
+Single source of truth for "is AACS bus encryption gone for this
+scan?". The gate asks ONLY this — `if !removed { error }` — never
+enumerating cases. Bus encryption is gone when ANY of these holds:
+the disc never had it; file/ISO reads (content already clear at read
+time); an unlocker unlocked the drive (it serves clear content); or
+the cert handshake produced the bus key. Add a NEW removal mechanism
+HERE, never in the gate.
+
+## AacsCertUnlocker
+
+libfreemkv-side driver for the AACS cert route. It owns the host-cert
+collection (a keysource concern that stays in libfreemkv) and then
+dispatches the actual mutual-auth to the `freemkv-unlock` AACS
+unlocker via the `crate::unlock_bridge`. The firmware (drive-prep) and
+CSS routes dispatch the same way at their own call sites; this one
+carries the host certs.
+
+## AacsCertUnlocker::authenticate
+
+Runs the host-certificate mutual-auth handshake: collect
+non-compiled-in host certs from the key sources + credentials, then
+hand them to the AACS unlocker (via the `freemkv-unlock` dispatch),
+which tries each cert (wedge-guarded) and on success yields the
+Volume ID + `read_data_key` (the AACS 2.0 bus key). Returns a
+`CertUnlockFailure` on every no-VID outcome.
+
+## unlock_error_to_error
+
+Maps a `CertUnlockFailure` back to the `Error` variant
+`do_handshake_cert` has always surfaced, so `scan_with`'s rendering
+and the path-1 disc-hash → VUK fallback are byte-for-byte unchanged.
+(`NoHostCert` keeps the `<no host cert>` sentinel.)
+
+## handshake_has_volume_id
+
+Did the cert handshake actually carry a Volume ID? Extracted so it can
+be tested as a VALUE. It only ever reaches an operator as the
+`has_volume_id` field of the `bus_key_unavailable` warn, and asserting
+on a `tracing` field means installing a capturing subscriber — which
+is thread-local, while `tracing`'s callsite-interest cache is global.
+Those two facts race: the test failed roughly one run in ten under the
+full parallel suite while passing every time in isolation, and
+serialising the captures was not enough because the cache can be
+re-evaluated against the process default rather than the thread-local
+dispatch.
+
+A predicate this small does not need a subscriber to verify. The
+polarity is the whole point: an `==` here would tell an operator a VID
+was absent on exactly the discs where one was present.
+
+## Disc::do_handshake
+
+SCSI handshake — drives the VID-acquisition flow and returns a
+structured `HandshakeResult` for downstream key resolution.
+
+VID acquisition runs through `do_handshake_cert`, which first uses the
+OEM VID a firmware unlocker may have stashed at drive `init()` (a
+drive-functionality capability decoupled from the host cert + HRL) and
+falls back to the cert-based mutual-auth handshake (dispatched to the
+`freemkv-unlock` AACS unlocker) when none is present. The cert path
+also yields `read_data_key`, required for AACS 2.0 bus decryption.
+
+Returns `(handshake, error)`:
+- `(Some(_), None)` — VID acquired
+- `(None, Some(_))` — specific failure mode (`AacsHostCertRejected` or
+  `AacsVidUnavailable`)
+- `(None, None)` — handshake not attempted (no keydb; resolution will
+  proceed with VID=zero and rely on path 1 disc-hash → VUK lookup)
+
+## Disc::do_handshake_cert
+
+Cert-based AACS handshake — the cert route for VID acquisition.
+
+Before running the cert mutual-auth, this checks for an OEM Volume ID
+a firmware unlocker stashed at drive `init()`. Such an unlocker
+unlocks *drive functionality*, not just the disc: VID retrieval via
+the drive's OEM CDB is a capability separate from `unlock`. When one
+served a VID, we use it and SKIP the cert handshake entirely — the
+OEM path gets the VID *without* the host certificate + HRL, decoupling
+VID from the cert chain. The OEM path yields no `read_data_key` (no
+bus-key is derived); AACS 2.0 content needing read_data_key for bus
+decryption must still use the cert path, so an unlocker with no OEM
+VID capability returns `None` and we fall through to cert auth
+unchanged.
+
+## Disc::collect_host_certs
+
+Collect every AACS host cert the caller carries, from BOTH the
+explicit `DriveCredentials` and the key-source layer
+(`crate::KeySource::host_certs` across each source), unioned. Host
+certs are keysource-served, never compiled in; this is the one place
+the OEM cert route gathers them. An empty result is the graceful
+no-cert signal (the caller turns it into `Error::AacsNoHostCert`).
+`mkb` is the disc's MKB generation when known, forwarded to each
+source's `crate::KeySource::host_certs` so a source MAY return only
+generation-appropriate certs (the default ignores it).
+
+## Disc::resolve_vid_only
+
+Build a keys-free AACS state that carries only the Volume ID (+
+version metadata), for callers that resolve Unit Keys out-of-band and
+have disabled the local keydb. The VID is on-disc content read during
+the handshake; preserving it here lets the out-of-band path use it. No
+keys are present (`unit_keys` empty, `vuk` None), so the disc reports
+as "encrypted, no keys" until the caller re-scans with a resolved Unit
+Key.
+
+## build_mkb (test helper)
+
+An MKB with one Type-and-Version record (type 0x10) carrying the
+version as BE u32 at record offset 8, followed by a recorded EOF
+record then trailing zero padding. mkb_content_len walks records and
+stops at the first padding (type 0) byte (aacs/inf.rs).
+
+## resolve_vid_only_no_cert_defaults_version_uhd (test)
+
+No content cert at all → version defaults to UHD (major 2), matching
+`read_aacs_version` so the scanned `AacsState.version` and the
+out-of-band fetch agree on the Unit_Key_RO stride (audit #4: a wrong
+BD-vs-UHD guess mis-parses unit keys). bus_encryption false
+(unreadable → off).
+
+## Skipped/deferred test coverage
+
+Tests for `read_vid_oem` (response parsing) are skipped in this file
+since `Drive` construction requires a live transport; parsing branches
+are exercised through `read_vid_oem`'s callers in integration. The
+`collect_host_certs` tests union `DriveCredentials` with the
+key-source layer; empty means the route fails gracefully
+(`AacsNoHostCert`).

docs/error-codes.md

@@ -0,0 +1,181 @@
+# Error Codes
+
+Overflow detail for `src/error.rs` doc comments that would otherwise exceed
+the comment-guard caps. Each section below is pointed to by a short `//` or
+`///` comment at the corresponding definition.
+
+## Error Code Ranges
+
+| Range | Category |
+|-------|----------|
+| E1xxx | Device errors |
+| E2xxx | Profile errors |
+| E3xxx | Unlock errors |
+| E4xxx | SCSI errors |
+| E5xxx | I/O errors |
+| E6xxx | Disc format errors |
+| E7xxx | AACS errors |
+| E8xxx | Keydb errors |
+| E9xxx | Stream/mux errors |
+
+## E_UDF_NO_USABLE_EXTENT
+
+A file that EXISTS and whose allocation descriptors resolved without error,
+yet yields not one usable extent: an empty AD list, or a list every entry of
+which is zero-length or points at LBA 0. Reported by the HD-DVD clip resolver
+(`disc::hddvd`).
+
+It has no `Error` variant on purpose. `UdfFs::file_extents` returns
+`Ok(vec![])` here rather than failing — the emptiness is only a defect in the
+eye of a caller that needs bytes — so the condition is DETECTED by the
+caller, not returned to it. The code exists so that detection can be
+accounted in the log with something other than a neighbouring error's code:
+logging it as E6017 would file a zero-length AD list as an authoring hole
+and send whoever triages it at the wrong population.
+
+## E_CSS_NO_DISC_KEY / CssNoDiscKey history
+
+While the disc-wide CSS failure and the per-title CSS failure both used
+`E_CSS_KEY_MISSING`, an uncrackable CSS disc was iterated title by title,
+each one logged as skipped, and the run exited reporting success — a total
+failure reported as success. `E_CSS_NO_DISC_KEY` / `Error::CssNoDiscKey` was
+split out so `is_disc_level_no_key` classifies it and a multi-title rip loop
+fails fast on it instead.
+
+## E_KEY_SERVICE_UNAVAILABLE
+
+A seven-hour run of HTTP 502s reported as `E_NO_DISC_KEY` told operators
+their disc was not in the key database and sent them hunting for a VUK that
+was never missing; the correct action was to wait. `E_KEY_SERVICE_UNAVAILABLE`
+exists so a key-source outage (transport error, DNS failure, timeout, TLS
+failure, HTTP 5xx, unreadable reply) is distinguishable from a source that
+answered and simply has no key.
+
+## E_MKV_SOURCE_INVALID vs E_MKV_INVALID
+
+`is_skippable_title_stub` classifies `E_MKV_INVALID` as a title that yielded
+no muxable frames, which an all-titles rip may skip while finishing the
+rest. A corrupt or truncated `mkv://` source file is a FAILURE, not a stub —
+reporting it as skippable would let a broken source be silently passed over
+by a run that then exits successfully. `E_MKV_SOURCE_INVALID` (and the
+sibling codes `E_MUX_HEADER_BUFFER_EXCEEDED`, `E_MKV_LACING_INVALID`) exist
+to keep that distinction, and are fatal.
+
+## UdfEmbeddedData
+
+A file that legitimately stores its data this way is tiny (an ICB caps it at
+well under 2 KiB — the AACS `*.inf` key files are the usual case), and the
+callers that expect one read it via `read_inline_data` long before extents
+are ever requested. A stream file cannot be one. `read_directory` already
+refuses the same shape for directories; `UdfEmbeddedData` is the file half
+of that decision.
+
+## MkvInvalid / MuxHeaderBufferExceeded history
+
+`MuxHeaderBufferExceeded` exists because hundreds of megabytes of real
+frames with unresolvable codec-init headers is NOT the same thing as
+`MkvInvalid`'s canonical case (an empty nav/menu PGC stub). Reporting the
+former as the latter would have `is_skippable_title_stub` silently drop a
+main feature from a rip that then exits successfully.
+
+## AacsBusKeyUnavailable
+
+NOT raised for AACS 1.0 BD (no bus encryption, `read_data_key` legitimately
+absent) nor for file-backed (ISO) scans, where bus encryption was already
+removed at read time and no handshake runs. Only a live-drive AACS 2.0/UHD
+scan that obtained the Volume ID but produced no bus key raises this.
+
+## SourceTerminated
+
+The alternative answer is a lie: a dead source that reports `Ok(0)` is
+indistinguishable from end-of-stream, and `DiscStream::fill_extents`
+legitimately reads a short count as a skippable hole — zero-filling and
+advancing over every remaining sector of the title and still returning
+success. Unlike a bad sector, this condition cannot be retried at a smaller
+size or skipped past.
+
+## error_code / From<Error> for io::Error round-trip
+
+`mux_stream` hands back an `io::Error`, and a front-end reporting *why* a
+title failed had no way to recover the code from it — the typed `Error` is
+gone by then and only the `E<code>` string prefix survives. Parsing that
+prefix is `error_code`'s job; every consumer re-implementing the parse is how
+the string-matching this crate spent 1.5.x removing comes back.
+
+`From<Error> for io::Error` boxes the typed value as the payload
+(`io::Error::new(kind, e)`), whose `Display` is the same `E<code>[: …]`
+string the stringifying version produced — so `error_code`'s parse is
+unaffected, and `From<io::Error> for Error` can additionally `downcast` the
+payload back to the exact typed error. Errors that did NOT come from this
+crate carry no `E<code>` prefix and yield `None`.
+
+## is_skippable_title_stub
+
+This replaces the CLI's `E7023`/`E6008` string-match with a typed check on
+the `io::Error` `mux_stream` returns.
+
+`Error::MkvSourceInvalid`, `Error::MkvLacingInvalid`, `Error::MkvUnencodable`
+all used to be raised as `Error::MkvInvalid` and therefore landed in the
+skippable set, so a corrupt source was reported as a title worth silently
+passing over by a run that then exited successfully. They now carry their
+own codes and are fatal, as is `Error::MuxHeaderBufferExceeded`.
+
+`Error::CssNoDiscKey` (the disc's CSS crack recovered no key at all) is the
+same conflation on the decrypt axis: while it too was raised as
+`Error::CssKeyMissing`, every title of an undecryptable disc classified as a
+skippable stub, so the rip loop skipped all of them and exited successfully.
+It belongs to `is_disc_level_no_key` instead, and is fatal here.
+
+## is_disc_level_no_key
+
+`E_CSS_NO_DISC_KEY` is the CSS side of the disc-level/per-title split, and it
+exists because the disc-wide CSS failure used to be raised as the per-title
+`E_CSS_KEY_MISSING`: an undecryptable CSS disc landed in
+`is_skippable_title_stub`, so the rip loop skipped all N titles with an
+"empty stub" notice and exited successfully.
+
+The key-SOURCE failures (`E_KEY_SERVICE_UNAVAILABLE`,
+`E_KEY_SERVICE_UNAUTHORIZED`, `E_KEY_SERVICE_RATE_LIMITED`) are classified
+here for the same fail-fast reason and NOT because they mean "no key": a
+service that is down, refusing the token, or throttling is down for every
+title on the disc, so iterating N titles re-issues N doomed requests (and,
+on 429, digs the rate-limit hole deeper). They are separate CODES precisely
+so the front-end can say "retry later" / "fix the token" instead of
+`E_NO_DISC_KEY`'s "no key source has a key for this disc".
+
+## is_marginal_read
+
+- MEDIUM ERROR (sense key 3) — canonical bad-sector signal.
+- ABORTED COMMAND (sense key B) — transient; retry usually works.
+- NOT READY (sense key 2) — the dominant bad-sector response on the BU40N
+  (ASC 0x04/ASCQ 0x3E); a pause + retry often recovers.
+- RECOVERED ERROR (sense key 1) / NO SENSE (sense key 0) — not classified as
+  fatal; treat as recoverable.
+
+Caller-agnostic predicate — describes a property of the *error*, not what
+one specific call site should do with it. Used by
+`freemkv_engine::recovery::copy`'s hysteresis dispatch.
+
+## Test rationale: declared_error_codes / uniqueness
+
+The uniqueness test used to carry a hand-maintained `vec![]` of the error
+constants, with a doc comment claiming it "pins all code assignments". It did
+not. At the time this was written the file declared 127 `pub const E_*` and
+the vector named 109 of them: eighteen codes — `E_DIR_IMAGE_FANOUT`,
+`E_DIR_INSUFFICIENT_SPACE`, `E_DIR_MULTIPASS_REJECTED`, `E_DIR_NAME_COLLISION`,
+`E_DIR_NAME_TOO_LONG`, `E_DIR_NOT_EMPTY`, `E_DIR_RAW_REJECTED`,
+`E_DIR_SOURCE_UNSUPPORTED`, `E_DIR_WRITE_FAILED`, `E_DRIVE_INQUIRY_SHORT`,
+`E_EMPTY_IMAGE`, `E_MP4_UNKNOWN_RESOLUTION`, `E_SEAM_PLAN_DROPPED_MOST`,
+`E_SHORT_IMAGE_READ`, `E_SINK_WROTE_NOTHING`, `E_SOURCE_TERMINATED`,
+`E_SYNC_TIMEOUT`, `E_SYNC_WORKER_LOST` — were outside the guarantee entirely,
+so a new variant colliding with any of them passed green. Worse, an earlier
+audit READ that doc comment and trusted it while assigning new codes.
+
+The defect is not the eighteen omissions, it is that the list is
+hand-maintained at all: adding a constant and forgetting the vector is a
+silent no-op, which is the definition of a guarantee that decays. Deriving
+the list from the declarations makes forgetting impossible — the only way to
+escape the check is to stop declaring the constant. `include_str!` of the
+same file is the cheapest seam that does that: no `build.rs`, no proc macro,
+no dependency, and — being `#[cfg(test)]` — not one byte of the source
+embedded in a release build.

docs/extract.md

@@ -0,0 +1,150 @@
+# `src/disc/extract.rs` — decrypted file-tree extraction
+
+## Relation to the ISO sweep/patch recovery passes
+
+`extract_tree` is a sibling of the disc→ISO sector dump (the sweep/patch
+recovery passes, which now live in the `freemkv-engine` crate), specialized
+to write **per file** rather than a whole image, applying decryption on the
+way out, and **without** any multipass / recovery orchestration — it is
+1-shot, decrypt-only.
+
+No new error codes are introduced: it reuses the existing `Error` set
+(`error.rs` is numeric-only, no English).
+
+## `extract_tree` contract details
+
+`reader` is consumed for content reads (it is moved into a
+`DecryptingSectorSource`); the structure + extent metadata are read first
+with the raw reader. `dest` receives the tree STRAIGHT IN (no auto-named
+subfolder). The caller must have run the pre-flight decrypt gate
+(`Disc::ensure_decryptable`); this method resolves per-VTS CSS keys itself
+for DVD.
+
+Bad sectors become recorded zero-filled holes in the affected file (the run
+does not abort); undecryptable units are counted as loss. Files are written
+`<name>.partial` and renamed on success, so an interrupted run never leaves
+a half-written file that looks complete.
+
+## `resolve_vts_key` — why a failed crack must be a hard error
+
+FALLIBLE, because the three outcomes of a crack are not two.
+[`crate::css::CrackOutcome`] exists precisely to separate "no scrambled
+sector was seen, so there is nothing to decrypt" from "scrambled sectors
+were seen and no key came out", and its doc says callers MUST surface the
+second as a hard error. An earlier version of this function used the
+`Option`-returning `crack_key`, which collapses both into `None`, and then
+fell back to the disc-wide key — descrambling this VTS with ANOTHER VTS's
+title key. The hazard is described in the ordering note in the function
+body, which was written about the same fallback; ordering makes the crack
+far more likely to succeed, but it cannot make a failed crack safe.
+
+## `Borrowed` — why a borrowing `SectorSource` wrapper
+
+Lets the decrypting decorator "own" an inner source for its lifetime while
+the caller keeps the underlying `&mut dyn SectorSource` (the decorator is a
+`DecryptingSectorSource<S>` generic over `S`, so it does NOT require a
+`'static` boxed inner — unlike the mux highway, which takes the reader by
+value). The decorator is dropped before `extract_tree` returns, so the
+borrow never escapes.
+
+## `whole_unit_batch` — the trailing-partial rule
+
+`remaining` is the sectors left in the current extent; the batch is capped
+at `READ_BATCH_SECTORS` and rounded DOWN to a whole number of 3-sector units
+UNLESS it is the extent's final (possibly short) tail — the tail always
+begins on a unit boundary, so a 1-2 sector partial there is handled by
+`decrypt_sectors`' trailing-partial contract. Used by `extract_one_file` so
+this rounding rule lives in exactly one place.
+
+## `available_space` (windows) — why the free-space gate matters
+
+Windows has no `statvfs`. This once returned `None` unconditionally, which
+does not merely skip a test — it skipped the free-space GATE, so a Windows
+user extracting a disc to a full volume got a confusing failure part-way
+through instead of a clear refusal up front. libfreemkv ships a Windows
+GUI, so that is the platform where the friendly error matters most.
+`FreeBytesAvailableToCaller` (not `TotalNumberOfFreeBytes`) is used because
+it accounts for per-user quotas, matching what `statvfs`'s `f_bavail` gives
+on the unix side.
+
+## `sanitize_component` — why reserved names are substituted, not rejected
+
+A name whose base matches a Windows reserved device name (`NUL`, `CON`,
+`COM1`..) is **substituted** (prefixed with `_`) rather than rejected — a
+Linux-authored disc may legally carry such a file and a single reserved
+name must not abort the whole tree walk. An empty result after stripping
+is an error.
+
+## `names_differing_only_by_case_are_a_collision` — why this must be an error
+
+Two disc names differing only by CASE are one host file on macOS APFS and
+Windows NTFS, both case-insensitive by default. Keyed by the case-preserving
+path, the collision map would see two entries, raise nothing, and the
+second file extracted would overwrite the first — while both `PlannedFile`s
+report `complete: true`. Silent data loss reported as a clean extract is
+the one outcome this crate must never produce, so the host-equivalence key
+has to model the host's namespace, not the disc's.
+
+## `a_files_partial_path_colliding_with_another_files_final_name_is_an_error`
+
+A disc carrying both `X` and `X.partial` plans two distinct final names, so
+nothing collides in the final-name check — but extracting `X` writes
+through `X.partial`, the same host path the other file owns. Whichever
+lands second truncates the other, and both entries would still be reported
+complete without this guard.
+
+## `multi_extent_aacs_anchors_unit_base_per_extent` — the alignment bug
+
+Regression (rc.6 audit, finding #449): a MULTI-EXTENT AACS file must
+re-anchor the unit-alignment base PER extent, not once at the first extent.
+The two extents in this test start at absolute LBAs whose difference is NOT
+a multiple of 3 (`PART_START+5000` vs `PART_START+5004` — a 4-sector delta).
+With a single first-extent unit base the second extent's first read is off
+the unit grid (offset 4, `4 % 3 == 1`) → `is_unit_aligned` fails →
+`DecryptFailed` → the whole extent becomes a zero-filled (false) hole. With
+per-extent anchoring both extents read clean: `bytes_unreadable == 0` and
+the file content survives. The fixture content is clear (no TS syncs) so
+the decrypt step restores each unit verbatim — this isolates the GATE from
+the cipher math.
+
+## `extract_tree_zero_fills_an_unrecorded_extent_instead_of_reading_it`
+
+An ECMA-167 4/14.14.1.1 type-1 extent is ALLOCATED BUT NOT RECORDED: the
+space belongs to the file and occupies its byte range, but nothing was ever
+written there, and the standard defines its contents as zeros.
+`read_icb_extents` keeps the flag (`IcbExtent::recorded`) and
+`read_file_limited` honours it by emitting zeros WITHOUT touching the
+media. The tree extractor reads the same ICBs and must agree: reading those
+sectors returns whatever the media happens to hold there — on an AACS disc,
+ciphertext that decrypts to noise — and writes it into the extracted file
+as if the disc had recorded it.
+
+## `per_extent_base_is_aligned_first_extent_base_is_not`
+
+Focused alignment-computation check underpinning the per-extent fix: when
+each extent anchors its OWN start as the unit base, the extent's own batch
+starts are always unit-aligned; anchoring a later extent against the FIRST
+extent's base mis-aligns whenever the extents' starts differ by a
+non-multiple of 3 sectors. This is the exact arithmetic the decrypt-on-read
+gate (`aacs::content::is_unit_aligned`) performs.
+
+## `css_two_vts_groups_do_not_cross_contaminate_keys`
+
+Regression: the per-VTS key crack in `resolve_vts_key` must gather ONLY
+this VTS's own title-VOB extents. Two VTS groups here carry DISTINCT
+scrambling keys; if the group filter (`vts_group_of(..) == Some(vts) &&
+is_title_vob(..)`) is loosened (`!=`, or `&&` -> `||`), one VTS's resolve
+gathers the OTHER VTS's extents, cracks the wrong key, and that VTS's own
+content silently fails to descramble to the expected plaintext.
+
+## `a_scrambled_vts_that_cannot_be_cracked_fails_instead_of_borrowing_a_key`
+
+A VTS that IS scrambled but whose key could not be recovered must FAIL, not
+borrow another VTS's key. `crack_key` returns `Option`, which collapses "no
+scrambled sector was seen" with "scrambled sectors were seen and no key
+came out"; the fallback then descrambled this VTS under the disc-wide key
+and `extract_tree` reported `complete = true` at exit 0, because no read
+had failed. `CrackOutcome` exists to keep those two apart, and every
+sibling path in the crate already honours it. The fixture: VTS_01 is
+crackable, VTS_02 is scrambled with NO periodic crib, so its crack
+genuinely fails.

docs/file-sector-source-linux.md

@@ -0,0 +1,36 @@
+# `file_sector_source::linux` — read-side platform hints
+
+## Why both `hint_sequential` and `drop_window`
+
+`POSIX_FADV_SEQUENTIAL` at open widens the kernel's readahead window so
+each pread aggregates into fewer NFS round-trips. `DONTNEED` on the
+consumed window (called periodically by the caller) drops the
+already-read pages from the page cache so an 85 GB streaming ISO read
+doesn't fill memory and starve concurrent writes (the MKV output
+during mux). Together they mirror the write-side WritebackPipeline's
+policy.
+
+## History
+
+Pre-Phase-1 (0.20.7 baseline) had both. Phase 1's introduction of
+`FileSectorSource` silently dropped the read-side DONTNEED, and
+0.21.2's revert of `SEQUENTIAL` (mistakenly attributing a regression
+to it) removed the hint. Net effect: 85 GB of ISO reads pinned in the
+page cache + no readahead widening → mux throughput collapse from
+18 MB/s historical to 2.7-8 MB/s on 0.21.x. Restored in 0.21.6.
+
+## `prefetch`
+
+Async-prefetch `len` bytes at `offset` into the page cache. The kernel
+`readahead(2)` syscall queues the I/O and returns immediately — it
+does NOT wait for completion. Called right after each consumed read
+so the next batch's I/O overlaps with the caller's processing of the
+current batch (decrypt + demux + mux).
+
+Without this hint, with a synchronous demux consumer running at
+~50 MB/s and a single-spindle disk capable of ~150 MB/s, the disk sits
+idle ~70% of each iteration because kernel readahead alone (capped at
+`/sys/block/<dev>/queue/read_ahead_kb`, default 128 KB) can only
+pre-stage a tiny slice of the next batch. An explicit `readahead()` of
+the same size as the current batch tells the kernel to queue the full
+next-batch read now.

docs/file-sector-source-macos.md

@@ -0,0 +1,29 @@
+# file_sector_source::macos
+
+macOS has no direct `POSIX_FADV_SEQUENTIAL` equivalent; the idiomatic hint is
+`fcntl(F_RDADVISE, &radvisory)` describing the byte range you intend to read
+soon. The open-time sequential hint points it at the whole file (clamped to
+`RDADVISE_MAX_BYTES` so a multi-TB ISO doesn't ask the kernel to prefetch
+everything at once).
+
+## RDADVISE_MAX_BYTES
+
+Cap on the byte length passed to `F_RDADVISE`. Asking for a multi-GB
+readahead window is counterproductive — the OS doesn't have that much cache
+to throw at one fd. 64 MiB is generous for our use case (sweep, mux) so the
+kernel's prefetch keeps pace with our app-level pipeline depth.
+
+## drop_window
+
+macOS has no direct `POSIX_FADV_DONTNEED` equivalent for a byte range.
+`fcntl(F_NOCACHE)` would disable caching globally on the fd (too coarse — we
+want the unread region to still benefit). Best approximation: no-op.
+macOS's unified buffer cache is generally less prone to the pin-everything
+pathology that triggers the regression on Linux NFS clients.
+
+## prefetch
+
+Async-prefetch the byte range `[offset, offset+len)`. macOS uses the same
+`fcntl(F_RDADVISE, &radvisory)` primitive as the open-time sequential hint,
+just targeted at a moving window instead of the whole file. The kernel
+queues I/O for the requested range and returns immediately.

docs/file-sector-source.md

@@ -0,0 +1,77 @@
+# `FileSectorSource` design rationale
+
+`FileSectorSource` reads 2048-byte sectors from an ISO file on disk via
+direct `seek + read_exact` (`pread`-equivalent) calls, letting the kernel's
+own readahead policy manage prefetch.
+
+## Why no app-level buffer
+
+Pre-0.21.3 this source held a 32 MiB (later 4 MiB) read-ahead buffer to
+amortise per-sector NFS round-trips. Empirically that buffer hurt: 32 MiB
+refills bursted the NFS TCP connection hard enough to starve the concurrent
+writer, and even a 4 MiB window gave the kernel less freedom to pipeline
+reads with writes. Direct pread per call lets Linux's readahead widen as it
+detects the sequential pattern, and naturally interleaves with writeback.
+
+## DONTNEED on the consumed window
+
+Without page-cache eviction an 85 GB streaming ISO read pins the entire
+file in memory, starves the concurrent writer, and collapses mux throughput
+(observed: 2.7 MB/s mux on 0.21.5 vs. 70 MB/s isolated NFS reads). Every
+`READ_DROP_CHUNK_BYTES_DEFAULT` of consumed bytes we call
+`posix_fadvise(DONTNEED)` over that window, mirroring the write-side
+`crate::io::writeback::WritebackPipeline` policy.
+
+The drop window is accounted by a monotonic forward byte counter, which
+matches the sequential streaming pattern the mux highway drives. Under
+random or backward access the dropped range no longer lines up with the
+bytes actually read — but `DONTNEED` is purely an advisory cache hint with
+no correctness impact, so this degrades to a slightly imprecise hint rather
+than a bug.
+
+`READ_DROP_CHUNK_BYTES_DEFAULT` (32 MiB) is the empirically tuned value on
+a 7200rpm HDD via SATA: smaller windows (8 / 16 MiB) shorten the
+kernel-readahead overlap and slow the producer; larger windows (64 / 128
+MiB) let the page cache pin enough of the ISO to pressure concurrent
+writes. Override via `FREEMKV_READ_DROP_CHUNK_MIB`.
+
+`READ_DROP_CHUNK_MIB_MAX` (64 GiB) bounds `FREEMKV_READ_DROP_CHUNK_MIB`
+before the MiB→byte multiply, mirroring `WRITEBACK_CHUNK_MIB_MAX`, whose
+identical multiply is bounded for exactly this reason: without the bound,
+a value above 2^44 overflows — a panic on the first ISO open in an
+overflow-checked build, and in release a wrap to a near-zero window that
+fires `drop_window` on every read. Out-of-range values fall back to the
+default.
+
+## Platform open hint
+
+On `open()` each platform issues its "sequential access expected" hint so
+OS-level readahead widens. The hint and the DONTNEED call live in per-OS
+sibling modules (`linux::hint_sequential` et al.) — no inline `#[cfg]` in
+this file.
+
+## Read-ahead prefetch
+
+After every consumed read we issue an OS-level prefetch hint for the next
+equivalent-sized window (`platform::prefetch`). The kernel queues that I/O
+asynchronously and returns immediately, so the next batch's read overlaps
+with the caller's processing of the current batch (decrypt + demux + mux).
+Without this the disk sits idle ~70% of each iteration because kernel
+SEQUENTIAL readahead alone (capped at `read_ahead_kb`, default 128 KB) is
+far smaller than our 16 MiB app-level batch.
+
+## Test notes
+
+- `read_sectors_with_an_undersized_buffer_errors_rather_than_panicking`:
+  this is a public `SectorSource` impl, so buffer length is caller input,
+  and the guard used to be a `debug_assert!` — compiled out in release,
+  where the `out[..bytes]` slice then panicked with 'range end index out
+  of range'. `Drive::read_fua` already carries this exact guard with a
+  comment recording the same panic being fixed there, and
+  `PrefetchedSectorSource` has `direct_read_too_small_buffer_errors` for
+  the same case; this impl had neither.
+- `dontneed_eviction_does_not_affect_data`: reads past the default 32 MiB
+  drop chunk (16384 sectors) so the eviction block fires at least once,
+  asserting every sector still reads correctly. Avoids mutating
+  `FREEMKV_READ_DROP_CHUNK_MIB` to sidestep a parallel-test env race with
+  `drop_chunk_size_env_override`.

docs/flac.md

@@ -0,0 +1,16 @@
+# FLAC elementary-stream decodability gate (`src/mux/codec/flac.rs`)
+
+FLAC frames carry no length field, so a raw stream is delimited only by
+sync-scanning + CRC validation. In freemkv, though, FLAC never arrives raw:
+it comes from mp4/mkv, where each packet is exactly one container-delimited
+FLAC frame (a complete, pre-delimited frame per packet). So this parser
+is a per-packet gate, not a framer: every FLAC frame ends with a 16-bit CRC
+(poly 0x8005, init 0, non-reflected) computed so the residue over the whole
+frame — footer CRC included — is zero (per the FLAC format specification,
+RFC 9639, frame footer). A nonzero residue is definitive corruption → drop
+the frame (a silence gap, never a shift — each packet keeps its own PTS),
+logged via the shared tally.
+
+A packet that does not begin with the FLAC frame sync is not a delimited
+frame we can validate, so it is passed through unchanged (never
+false-dropped).

docs/fmp4-mod.md

@@ -0,0 +1,36 @@
+# fMP4 muxer (`src/mux/fmp4/mod.rs`) — stub status and design notes
+
+## Status
+
+**STUB**. The muxer can emit the init segment (`ftyp` + a minimal HEVC
+`moov` skeleton with one video track) via
+[`Fmp4Mux::write_init_segment`], so the shape and call site are
+validated, but media fragments (`moof`/`mdat`) are NOT emitted.
+[`Fmp4Mux::write_video`] therefore returns
+[`Error::Fmp4Unimplemented`](crate::error::Error::Fmp4Unimplemented)
+rather than silently accepting and discarding frames. It buffers
+nothing, so it cannot accumulate memory.
+
+## Not yet implemented
+
+- `moof` box: `mfhd` (sequence_number) + `traf` (`tfhd` + `tfdt`
+  + `trun` with sample sizes, durations, flags, composition offsets).
+- `mdat` box: concatenated sample data.
+- Fragment cadence: one fragment per GOP or every N seconds,
+  whichever comes first.
+- HEVC `hvcC` box inside `moov.trak.mdia.minf.stbl.stsd` so the
+  init segment is self-describing (`stsd` currently has zero entries).
+- Sample-flags computation (sync vs. delta, depends_on, etc.).
+- Edit lists / fragment_duration for accurate seeking.
+
+Reference: ISO/IEC 14496-12 §8 (Movie Fragments).
+
+## `wrap_box` size-cast rationale
+
+All callers build tiny init-segment boxes (kilobytes at most), so the
+`u32` size never overflows; the saturating cast plus the debug assert
+documents and guards that invariant rather than silently emitting a
+truncated, structurally corrupt size field. `body` is always
+internally constructed here, never untrusted input — a future caller
+feeding a multi-gigabyte body trips the debug assert instead of
+writing a malformed box.

docs/fox.md

@@ -0,0 +1,70 @@
+# Fox — `dcx.xml` label parser
+
+Older Fox authoring (e.g. a real Fox release, `/BDMV/JAR/05001/dcx.xml`) ships a
+human-readable XML manifest alongside the BD-J jar. Its root is `<dcx>`, and
+under `<disc>` it lists every playlist the disc plays. The main-feature
+playlists carry nested per-stream `<audio>`/`<subtitle>` elements naming
+language, editorial purpose and forced/SDH state outright — everything a
+label parser wants, in attributes, with no bytecode to walk.
+
+NOT A SPECIFICATION. `/BDMV/JAR/` is application-defined space, so this file
+is one authoring house's internal metadata that happens to press onto the
+disc. Every field meaning below was read off a real disc; treat an
+unfamiliar value as unknown rather than guessing.
+
+## Confirmed schema
+
+A real Fox release, `/BDMV/JAR/05001/dcx.xml`:
+
+```xml
+<dcx>
+  <disc>
+    <playlist id="00001" lang="eng" name="topmenu"/>
+    ...
+    <playlist id="00800" lang="eng" name="feature" vers="1" durs="7628">
+      <audio id="01" lang="eng" type="feature"/>
+      <audio id="02" lang="eng" type="rnib"/>
+      <audio id="03" lang="spa" dial="lat" type="feature"/>
+      ...
+      <subtitle id="01" lang="eng" type="feature" form="sdh"/>
+      <subtitle id="02" lang="spa" dial="lat" type="embed"/>
+      ...
+      <subtitle id="11" lang="eng" type="text"/>
+      <properties> ...chapter marks... </properties>
+    </playlist>
+    <playlist id="00801" lang="jpn" name="feature" vers="1" durs="7628"> ... </playlist>
+  </disc>
+</dcx>
+```
+
+## Field meanings (read off the disc, not documented)
+
+* `<audio type>`: `feature` = a normal program track; `rnib` = a
+  descriptive/narration track ("Royal National Institute of Blind People"
+  described-video), mapped to `LabelPurpose::Descriptive`. A `type`
+  containing "comment" maps to `LabelPurpose::Commentary`.
+* `<subtitle form>`: `sdh` marks a subtitles-for-the-deaf-and-hard-of-
+  hearing track (`LabelQualifier::Sdh`).
+* `<subtitle type>`: `embed` marks a dedicated forced/embedded-subtitle
+  track (`LabelQualifier::Forced`); `feature`/`text` are full tracks.
+* `id` on a nested stream is its 1-based STN slot WITHIN ITS TYPE
+  (audio ids 01..N, subtitle ids 01..N independently), matching the vendor
+  `stream_number` convention the ordinal binder in `super::apply_labels`
+  reads.
+
+The `<audio>`/`<subtitle>` elements are NESTED inside one feature playlist,
+so extraction is scoped to a single `<playlist name="feature">` element —
+never a document-wide `<audio>` scan, which would merge the regional
+`00800` (eng) and `00801` (jpn) tables into one and collide their slots.
+
+## `select_feature_playlist` scoping rationale
+
+Among all `<playlist name="feature">` elements — Fox presses one per
+regional variant (`00800` eng, `00801` jpn) — the one carrying the most
+`<audio>`/`<subtitle>` streams wins, ties to the first.
+
+Returning ONE element is the whole point: each feature playlist is its own
+STN table with its own 1-based slot ids, so merging two would put two
+different streams on slot `01`. The richest table is the fullest label set
+and anchors to its matching title by language sequence in
+`super::apply_labels`.

docs/fs-type-linux.md

@@ -0,0 +1,13 @@
+# Linux `f_type` classification
+
+`classify_f_type` in `src/platform/fs_type/linux.rs` is the single source of
+truth for the magic-number comparisons used by both the path-based
+(`detect_impl`) and fd-based (`detect_fd_impl`) entry points.
+
+## Why the `i64` cast
+
+`statfs::f_type` is signed `__fsword_t` on glibc and unsigned `c_ulong` on
+musl; a portable comparison needs a common type, so the value is cast to
+`i64`. On glibc x86_64 both are already `i64` — clippy flags the cast as
+unnecessary on that target only, but the cast is required for musl, hence
+the `#[allow(clippy::unnecessary_cast)]`.

docs/fs-type.md

@@ -0,0 +1,12 @@
+# fs_type module
+
+The buffering architecture (Phase 2) selects different output sinks
+for local vs network filesystems: NFS gets the adaptive
+`WritebackFile` machinery on Linux; local disks get `LocalFileSink`
+and rely on the kernel's default writeback policy. This module
+provides the construction-site primitive that picks which one.
+
+Per the per-OS file-split convention, the actual `statfs` call lives
+in the matching platform file (`linux.rs`, `macos.rs`, `windows.rs`,
+`other.rs`); this `mod.rs` exposes only the cross-platform enum and
+the `detect` entry point.

docs/fsync.md

@@ -0,0 +1,20 @@
+# `io::fsync` — platform-aware crash-durability primitives
+
+Two flush operations need OS-specific handling to make a write survive a
+crash / power loss:
+
+- **`dir`** — fsync a directory so a prior `rename(2)` into it is durable.
+  After a crash a renamed file's dirent can otherwise be lost even though
+  the rename returned, because it is still page-cache-only. This is a POSIX
+  concept: on Windows std cannot even open a directory as a `File` (it does
+  not set `FILE_FLAG_BACKUP_SEMANTICS`), and NTFS/ReFS commit the rename's
+  dirent without an explicit directory flush — so it is a no-op there
+  rather than a failed open that logs on every marker write.
+
+- **`file_durable`** — fsync a file's contents + metadata. Opens the file
+  **read+write**: on Windows `File::sync_all` maps to `FlushFileBuffers`,
+  which requires a handle with write access and returns
+  `ERROR_ACCESS_DENIED` (os error 5) on a read-only handle. (A read-only
+  `File::open` + `sync_all` is legal on POSIX, which is why that bug only
+  bit Windows.) The open mode is platform-uniform, so this lives here with
+  no dispatch.

docs/fvi-sink.md

@@ -0,0 +1,37 @@
+# `fvi://` sink notes
+
+Rationale and design notes for `src/mux/fvi_sink.rs` that don't belong in the
+public rustdoc contract.
+
+## Relationship to `VideoMap`
+
+The sink is a thin consumer of the reusable, pure-data
+[`VideoMap`](crate::mux::videomap) model
+([`MapHeader`](crate::mux::videomap::MapHeader) /
+[`PictureRecord`](crate::mux::videomap::PictureRecord)): it builds the header
+from the title, then writes one record per video
+[`PesFrame`](crate::pes::PesFrame) straight to disk. Nothing here re-parses
+the elementary stream, and the whole index is never buffered.
+
+Serialization is inlined in the sink itself.
+
+## Extensibility
+
+A different output format would be a DIFFERENT sink reusing the same
+`VideoMap` model (e.g. a future `fvi2://`), not a pluggable encoder —
+extensibility is by adding a sink, like every other sink in this crate.
+
+## `write_fvi_record`: coding-derived members (§7.1)
+
+Coding-derived members (§7.1) are produced via the codec-agnostic
+`PictureInfo` accessors, never the raw bitstream: `field_order` is emitted
+only when measured (OMITTED on codec-type-only HEVC/H.264/VC-1),
+`progressive` only when signalled.
+
+## `write_fvi_record`: `dts` / future `recovered` member
+
+`dts` is MAY per the format spec — the highway carries no DTS on a frame, so
+it is always omitted.
+
+TODO(provenance→recovery join): a `recovered` MAY member (sweep/patch mapfile
+overlap with this AU's `src`) belongs here; unreachable at `PesFrame`.

docs/h264.md

@@ -0,0 +1,189 @@
+# H.264 codec parser notes
+
+## Slice-type mapping
+
+`h264_slice_coding_type` maps an H.264 `slice_type` (Rec. ITU-T H.264 §7.4.3,
+Table 7-6) to a coding type. Values 5..=9 repeat 0..=4 (the "all slices of
+this type" forms), so `slice_type % 5`: 0 = P, 1 = B, 2 = I, 3 = SP
+(predicted → P), 4 = SI (intra → I). Returns `None` for values outside 0..=9
+(malformed header).
+
+## `unescape_ebsp_prefix`
+
+Copies the leading bytes of an EBSP with emulation-prevention bytes removed
+(ISO/IEC 14496-10 §7.3.1: a 0x03 following 0x00 0x00 is not part of the
+RBSP). Only a short prefix is produced, because the sole caller decodes two
+ue(v) fields from the very start of a slice header. `first_mb_in_slice` and
+`slice_type` are each at most 32 bits, so 16 octets is ample and keeps this
+off the per-frame allocation path for anything larger.
+
+## `unescape_ebsp`
+
+Copies `ebsp` with emulation-prevention bytes removed, stopping after at most
+`max_octets` output bytes (pass `ebsp.len()` for "no cap").
+
+The zero run-length counter is cumulative across the whole scan and is reset
+only when an escape byte is actually dropped — matching the reference
+decoding process in ITU-T H.264 §7.3.1, which discards a 0x03 following ANY
+run of two-or-more 0x00 bytes, not just an exact `00 00 03` sliding window. A
+window-based scanner that advances by 3 on a match and by 1 otherwise
+disagrees with this on a run of 3+ real zero bytes ahead of an 0x03:
+`00 00 00 03` decodes here as `00 00 00` (the run is escaped, matching every
+other H.264 decoder), where a window scan starting fresh after each
+non-match would keep the 0x03 as real payload. Only one implementation of
+this rule may exist in this module — see `parse_sps_high_profile_ext`, which
+used to keep its own window-scan copy that disagreed with this one on
+exactly that input.
+
+## `handle_param_set`
+
+Handles an SPS/PPS NAL (mirrors the HEVC fix). The strip/emit decision is
+made against the currently-ACTIVE set `cur`, NOT the codecPrivate copy
+`first`: a streaming MKV decoder applies avcC once at init and thereafter
+updates a parameter set only from an in-band NAL, so a switch BACK to the
+first-seen body (== codecPrivate) is still a change the decoder must be told
+about. Stripping on `== first` silently dropped that revert.
+
+- First of its type → seeds codecPrivate; stripped (decoder gets it from avcC).
+- Equal to the active set `cur` → redundant; stripped.
+- Different from `cur` (a change in EITHER direction) → emitted in-band and
+  `cur` updated.
+
+Returns `true` when the NAL was emitted in-band into `frame_data`.
+
+## `reassert_active`
+
+Appends the active parameter set `cur` to `prefix` (length-prefixed) so
+every keyframe is SELF-CONTAINED: it carries the active SPS/PPS in-band
+ahead of its slices. Skipped only when this access unit ALREADY carried the
+NAL in-band (`emitted` — avoids a duplicate) or no active set exists yet.
+
+Unconditional (not only when the active set differs from codecPrivate): a
+streaming decoder applies the avcC param sets once at init, then relies on
+in-band repetition. Some sources stop repeating a param set at later IDRs
+even though its body is unchanged; if the decoder then drops it (a reset
+event), nothing re-sends it and every subsequent slice fails (param-set id
+out of range) until the next genuine change. Re-asserting at EVERY keyframe
+— what compliant muxers do at every IDR — makes streaming decode
+self-healing. Re-sending an identical param set is benign; cost is a few
+bytes per keyframe. This strictly supersets the change-only re-assert, so
+the param-set-revert fix is unaffected.
+
+## `parse_sps_high_profile_ext`
+
+Parses `(chroma_format_idc, bit_depth_luma_minus8, bit_depth_chroma_minus8)`
+from a High-Profile SPS NAL (profile_idc ∈ `HIGH_PROFILES` — the 14
+chroma/bit-depth extended profiles `codec_private` invokes this for).
+
+SPS RBSP layout (ITU-T H.264 §7.3.2.1.1) up to the fields we need:
+
+```
+byte 0        NAL header (already known to be type 7)
+byte 1        profile_idc
+byte 2        constraint_set_flags / reserved
+byte 3        level_idc
+ue(v)         seq_parameter_set_id
+— High-profile branch —
+ue(v)         chroma_format_idc
+if chroma_format_idc == 3: u(1) separate_colour_plane_flag
+ue(v)         bit_depth_luma_minus8
+ue(v)         bit_depth_chroma_minus8
+```
+
+RBSP emulation-prevention bytes (0x00 0x00 0x03 → 0x00 0x00) are removed
+before bit-parsing so the bit reader sees clean RBSP data.
+
+Returns `None` if the SPS is too short or malformed (Exp-Golomb code
+overflows 32 bits, leading-zero count > 31, etc.). The caller silently omits
+the extension in that case.
+
+## Test notes
+
+### `open_gop_intra_access_unit_is_a_keyframe`
+
+Open-GOP resync fix: a non-IDR intra-coded access unit MUST be flagged a
+keyframe so the B1 resync gate (`mux/resync.rs`) can disarm on a BD
+open-GOP tail instead of dropping every frame to EOF and truncating the
+video. BD H.264 titles reach random access at a non-IDR I-frame (the
+recovery point); HEVC gets this free from the CRA NAL type, H.264 does not,
+so the measured intra coding type is the signal. Red before the intra
+promotion in `parse` — a non-IDR I-slice used to yield `keyframe == false`.
+
+### `inter_coded_access_unit_is_not_a_keyframe`
+
+Guards the promotion's precision: a non-intra (P) access unit must NOT be
+promoted to a keyframe, or the resync gate would resume on a frame that
+carries inter-references to dropped data and the MKV cue index would gain
+bogus random-access points.
+
+### `slice_header_parse_removes_emulation_prevention_bytes`
+
+The slice-header parse must remove emulation-prevention bytes first
+(ISO/IEC 14496-10 §7.3.1/§7.4.1): the payload after the NAL header is EBSP,
+and a 0x03 following 0x00 0x00 is not part of the RBSP.
+
+Reachable when `first_mb_in_slice` is 65535 or more — a ue(v) that needs
+sixteen leading zero bits, so the payload opens 0x00 0x00 and an encoder
+must escape it. A UHD frame is ~32,400 macroblocks so conforming Blu-ray
+never gets there, but 8K does, and the disc is untrusted input. Reading the
+raw NAL decoded `slice_type` against the inserted byte and produced the
+wrong picture type.
+
+### `unescape_ebsp_drops_escape_after_a_run_of_three_zeros`
+
+Regression: `parse_sps_high_profile_ext` used to re-derive the
+emulation-prevention rule with its own window scanner (match `00 00 03` at
+position i, advance by 3; else advance by 1) instead of calling the shared
+`unescape_ebsp`. On a run of 3+ real 0x00 bytes ahead of an 0x03 —
+non-conformant, but this is untrusted disc input, not a spec-clean encoder —
+the two disagreed: `unescape_ebsp`'s cumulative zero counter (the rule the
+H.264 reference decoding process in §7.3.1 specifies) drops the 0x03 as an
+escape, while a fresh 3-byte window starting right after the non-matching
+first byte kept it as real payload. Pin the shared function's behaviour
+here so a second hand-rolled copy doesn't quietly reappear.
+
+### `keyframe_param_reassert_emits_exact_bytes`
+
+The keyframe SPS/PPS re-assert must produce EXACTLY these bytes: the active
+SPS, then the active PPS, then the access unit's own NALs, each as a 4-byte
+big-endian length prefix followed by the NAL body (ISO/IEC 14496-15
+length-prefixed form, lengthSizeMinusOne = 3).
+
+This pins the full byte string, not just its length, so the in-place
+`splice` that replaced the build-a-new-buffer-and-copy approach is proven
+byte-for-byte equivalent — including the ORDER (parameter sets ahead of the
+slices, which is what makes the keyframe self-contained). The literals were
+captured from the pre-splice implementation's output.
+
+### `keyframe_param_reassert_does_not_reallocate_the_frame`
+
+MEASURED: the keyframe parameter-set re-assert must be spliced into the
+front of the already-assembled access unit IN PLACE, not built as a fresh
+full-size buffer.
+
+It used to `prefix.extend_from_slice(&frame_data)` and then replace
+`frame_data` with `prefix`, which grew a few-hundred-byte `prefix` to the
+FULL access-unit size — a fresh multi-hundred-KB allocation — memcpy'd the
+whole frame into it, and dropped the presized buffer. One extra whole-frame
+allocation plus one extra whole-frame copy per keyframe: a UHD title is
+~200,000 frames of 150-400 KB with a keyframe every 1-2 s, i.e. thousands of
+avoidable multi-hundred-KB copies per title, each large enough to go through
+mmap. `PARAM_REASSERT_HEADROOM` exists so the splice never reallocates; this
+counts the reallocations that happen, which must be zero. Mirrors the HEVC
+parser's test of the same name.
+
+### `avcc_profile_244_appends_extension_bytes`
+
+ISO 14496-15 §5.3.3.1.2 regression: profile_idc=244 (High 4:4:4 Predictive)
+ALSO mandates the chroma/bit-depth extension. It was missing from
+HIGH_PROFILES, so a 244 stream took the Baseline/Main path and emitted an
+avcC with NO extension bytes — non-conforming, and strict parsers then
+assume 8-bit 4:2:0. The extension must be appended.
+
+### `sps_reader_read_ue_thirty_one_leading_zeros_is_still_valid`
+
+`SpsReader::read_ue`'s truncation guard is `leading_zeros > 31`: 31 leading
+zero bits is the longest legal code and must decode, not abort. Mirrors the
+equivalent guard in the shared `BitReader` in `startcode.rs`, kept here
+because `SpsReader` is a separate, unshared implementation used only for SPS
+parsing.

docs/halt.md

@@ -0,0 +1,16 @@
+# halt
+
+## Why `Ordering::Relaxed`
+
+`Ordering::Relaxed` is sufficient on both load and store because this flag
+is purely advisory — no other memory operations piggyback on it for
+happens-before ordering. Callers that need to publish data across threads
+do so via channels or other synchronization, not via this bit.
+
+## Why 250ms for `POLL_INTERVAL`
+
+250 ms is the sweet spot between responsiveness (operator presses Stop,
+sees it take effect within ~quarter-second) and waste (atomic load + clock
+read is cheap but not free at thousands of hertz). It's centralised here
+so the half-dozen halt-polling loops across `io` can't drift apart
+silently.

docs/harness.md

@@ -0,0 +1,35 @@
+# Seeded robustness harness (`src/harness.rs`)
+
+Every parser reached from here takes bytes that came off a disc, and this
+crate's primary boundary is that the disc is untrusted: a malformed, damaged
+or hostile image must never crash the library. These tests assert exactly
+that one property — the parser returns `Ok` or `Err`, and never panics.
+
+## Why this exists rather than `cargo-fuzz`
+
+`cargo-fuzz` needs a nightly toolchain (`-Zsanitizer` plus SanitizerCoverage
+for libFuzzer's coverage feedback) and this project pins stable. So the
+generator lives here instead. It gives up coverage-guided mutation — the real
+loss — and keeps everything else: millions of cases, structure-aware input,
+and a crash corpus. It also gains determinism, which a fuzzer does not have:
+the same seed replays the same cases on any machine.
+
+## Why no `proptest` or `arbitrary`
+
+This crate has exactly one dev-dependency. That is a deliberate posture, and
+a randomness crate is not worth ten transitive dependencies when the parsers
+take plain `&[u8]` and a good enough generator is forty lines.
+
+## Budget
+
+`FREEMKV_HARNESS_CASES` sets cases per generator per target (default 256, low
+enough that the per-commit gate stays under a second). The overnight run sets
+it to millions. `FREEMKV_HARNESS_SEED` overrides the seed; the default is
+fixed so a failure in CI reproduces locally verbatim.
+
+## On failure
+
+The panic message carries the seed, generator and case index. Re-run with
+`FREEMKV_HARNESS_SEED=<seed>` to reproduce, then write the offending bytes
+into `tests/corpus/` as a permanent regression fixture — discovery happens
+here, defence happens there.

docs/hddvd.md

@@ -0,0 +1,465 @@
+# HD-DVD title scanning (`src/disc/hddvd.rs`)
+
+HD-DVD is a **tree-level peer** of DVD and Blu-ray (not a stream variant like
+FMTS): its content lives in `HVDVD_TS/` as `.evo` clips — Enhanced VOB, an
+MPEG **program** stream — each with a small `.map` timemap sidecar, navigated
+by `.xpl`/`.ifo` playlists in `HVDVD_TS/` and `ADV_OBJ/`. Because it is a
+different tree with a different playlist format, it gets its OWN scanner
+(this file), a peer to `Disc::scan_bluray_titles` — the two-format design
+rule: a genuinely different format is a new enumerator, not an extension
+bolted into the BD path.
+
+## Title composition (authoritative path)
+
+Title composition is authoritative, from the Advanced-Content playlist. HD-DVD
+ships a real player playlist at `ADV_OBJ/VPLST000.XPL` (DVD-Forum
+`HDDVDVideo/Playlist` XML). The scanner parses it (with a real XML parser,
+`roxmltree`) into one `DiscTitle` per `<Title>`: its `<PrimaryAudioVideoClip>`
+clips in playback order (each an EVO, referenced via its `.MAP` sidecar), the
+`titleDuration`, the `displayName`, and the `<ChapterList>`. A layer-break
+split (`FEATURE_1` + `FEATURE_2`, or `feature`/`feature_Divide`) is composed
+into ONE title with the two parts as clips, carrying each clip's title-time
+in/out points (45 kHz ticks) so a seamless join can be spliced onto one
+timeline. Container is `ContentFormat::MpegPs`, so the existing PS mux path
+handles it. Per-clip streams are enumerated by demuxing the clip head and
+building one `Stream` per distinct elementary stream (video + DD+ audio),
+codec sniffed from the ES bytes.
+
+## Fallback path
+
+When no playlist is present (or it fails to parse), the scanner falls back to
+the older clip-name heuristic: parse the `HVA*.VTI` clip table, join the
+`feature*`-named clips into one title, and emit every other clip on its own.
+
+## Known gaps
+
+Not parsed yet: subtitles (8-bit RLC on `0xBD` sub `0x20..=0x3F`) and per-track
+audio languages (the XPL carries `<Audio description=...>` but they are not yet
+wired onto the streams). Extents and size are real (the ripper images the
+clips).
+
+## VTI parsing
+
+`parse_vti_clip_order` parses the `ADVANCED-VTS` VTI clip-name table. The
+table is a run of `VTI_CLIP_ENTRY_STRIDE`-spaced records, each carrying a
+NUL-terminated `<name>.EVO`. Rather than trust the (imprecise) header pointer,
+it collects every NUL-terminated `*.EVO` name and keeps the largest group
+sharing one residue modulo the stride — the clip table — in offset order.
+Returns empty for a non-VTI blob or one with no recognizable table.
+
+## Codec sniffing
+
+`sniff_video_codec` reads MPEG / Annex-B start codes: `00 00 01 B3` → MPEG-2
+(sequence_header), `00 00 01 0F` → VC-1 (BD/HD-DVD sequence-header BDU),
+`00 00 01 [x7]` H.264 SPS NAL (type 7, forbidden_zero_bit clear) → H.264.
+Returns `None` when no recognizable start code is present. The scan prefers
+the unambiguous MPEG-2 / VC-1 sequence headers; H.264 is inferred from an SPS
+NAL so a stray slice/picture code can't be mistaken for a different codec.
+
+`sniff_audio_codec` recognizes only Dolby Digital Plus (E-AC-3) today, via its
+`0x0B77` syncword — what real retail HD-DVD titles carry on sub-ids
+`0xC0..=0xC7`. Returns `None` for an unrecognized sample so the caller drops
+the stream rather than mislabeling it.
+
+## probe_evo_streams
+
+Demuxes the head of an `.evo` clip (through the disc's `SectorSource`) and
+builds one `Stream` per distinct elementary stream found: the video track
+(mapped to the canonical `DVD_VIDEO_PID` for plain 0xE0-0xEF video, or the
+extended-stream-id PID for HD-DVD VC-1) and every DD+ audio sub-stream
+(mapped via `dvd_audio_pid`). Codec is sniffed from the demuxed ES bytes.
+
+Mirrors the stream construction in `Disc::scan_dvd_titles`; resolution /
+language / channels use sane HD-DVD defaults (the muxer reads the true pixel
+dimensions from the H.264 SPS, and E-AC-3 channel counts are not decoded
+here). Returns an empty vec when the clip cannot be read or carries no
+recognizable stream (e.g. an AACS-encrypted clip probed as ciphertext).
+
+Cancellation is checked before every chunk read and is the ONE condition that
+returns `Err` rather than an empty vec: a probe cut short by a Stop has not
+established that the clip carries no streams, and reporting it as if it had
+would enumerate a stream-less title as a scanned fact. A read that fails for
+any other reason keeps the existing best-effort behaviour.
+
+## collect_es
+
+VC-1 video rides extended-stream-id `0xFD` with `stream_id_extension` `0x55`.
+HD audio (MLP/TrueHD) can also use `0xFD` with other extensions — routing
+those to their own audio tracks is deferred (see the HD-DVD program-chain
+follow-up); until then only the VC-1 extension is treated as video, so an
+audio `0xFD` sub-stream can never mis-stamp the video PID.
+
+## XPL amplification bounds
+
+The XPL parser guards against a crafted `ADV_OBJ/VPLST000.XPL` amplifying a
+small file into an enormous amount of work or memory. Four separate axes are
+bounded, each independently, because they are separate attacks:
+
+- **`MAX_XPL_DEPTH` (32)** bounds element NESTING. A real `VPLST000.XPL` is
+  about six levels deep at its deepest
+  (`Playlist`/`TitleSet`/`Title`/`PrimaryAudioVideoClip`/`Video`, or
+  `.../ChapterList/Chapter`); 32 leaves a 5x margin for authoring tools that
+  wrap extra `ApplicationSegment`/`ObjectMappingList` layers, while staying
+  trivially stack-safe.
+
+- **`MAX_XPL_TITLES` (512)** bounds how many `<Title>` elements one playlist
+  may declare — BREADTH, separate from the depth guard: a flat playlist
+  passes the depth check trivially and can still declare a title per 51
+  bytes, so a 64 MiB `VPLST000.XPL` (exactly `udf::MAX_FILE_BYTES`) reaches
+  ~1.3 million of them. This matters here and not on the Blu-ray side because
+  of where the count comes from: `bluray.rs` learns its playlists from the
+  MPLS files actually present in the UDF directory, so the medium bounds it —
+  an XPL DECLARES its titles, so nothing does. The cost is drive time, not
+  memory: `compose_xpl_titles` runs `probe_evo_streams` once per title, and
+  each probe reads real sectors, so an uncapped count turns a `Disc::scan()`
+  the operator expects to take seconds into tens of terabytes of optical
+  reads on a disc that is only pretending to be large. The bound that matters
+  is `cap x EVO_PROBE_SECTORS`, since `compose_xpl_titles` memoizes on the
+  title's RESOLVED extent list, and distinct titles built from different
+  combinations of the same clips have different lists, so each one misses the
+  memo — at 4096 that product was 64 GiB of optical reads, the same worst
+  case, and the same contradiction with "seconds", as the sibling
+  `MAX_HDDVD_CLIPS` path. 512 keeps it at 8 GiB and remains far above any
+  real disc (retail HD-DVDs carry tens of titles).
+
+- **`MAX_HDDVD_CLIPS` (512)** caps `.evo` clips taken from the `HVDVD_TS/`
+  directory listing. `MAX_XPL_TITLES` and `xpl_depth_within_limit` bound the
+  `ADV_OBJ/*.XPL` path, but a crafted disc simply omits `/ADV_OBJ`; control
+  then reaches the clip-name fallback in `Disc::scan_hddvd_titles`, which
+  emits one title per directory entry and probes each — the same unbounded-
+  probe cost, reached without the playlist. The directory is the only bound
+  the medium supplies, and `udf::MAX_DIR_BYTES` (1 MiB) still leaves room for
+  ~24,000 FIDs. Memoizing the probe (`EvoProbeCache`) collapses entries that
+  resolve to the SAME extents, closing the many-names-one-File-Entry case —
+  but not this one: a File Entry is a single sector, so an attacker can give
+  every FID its own, each declaring its own extent, for ~48 MiB of image;
+  every probe then misses the memo and costs a full `EVO_PROBE_SECTORS`
+  (16 MiB) read, hundreds of GiB on a scan the operator expects to take
+  seconds. The cap's job is to bound `cap x EVO_PROBE_SECTORS`; it was 4096
+  (matching `MAX_XPL_TITLES`, which bounds a different, no-per-item-read-cost
+  path) — 4096 x 16 MiB is 64 GiB, more than dual-layer HD-DVD media
+  physically holds (reachable anyway, since distinct extent lists may overlap
+  on the medium). 512 keeps the product at 8 GiB and still leaves a wide
+  margin over any real disc (retail HD-DVDs carry TENS of `.evo` clips, ~10x
+  the real-world maximum, the sizing convention `MAX_XPL_CHAPTERS_PER_TITLE`
+  also uses against the 99-chapter authoring ceiling). Pinned by
+  `the_clip_cap_and_probe_budget_bound_a_scans_worst_case_read_volume`, which
+  asserts the PRODUCT rather than either constant, so raising one without
+  re-examining the other fails.
+
+- **`MAX_XPL_CLIPS_PER_TITLE` (256)** bounds how many
+  `<PrimaryAudioVideoClip>` elements a SINGLE `<Title>` may contribute — the
+  fourth amplification axis, the one the other three guards leave open. A
+  64 MiB XPL holds ~1.7 million `<PrimaryAudioVideoClip src="A.EVO"/>`
+  elements at ~38 bytes each, and the collector is `descendants()`, not
+  `children()`, so a clip nested inside N ancestor `<Title>` elements is
+  collected by EVERY one of them — the depth cap still permits 32 such
+  ancestors (measured: a bare `<Title>` root nests 32 deep and still parses,
+  because the guard counts the self-closing clip element as non-nesting).
+  The product is ~1.7M x 32 ≈ 56 million heap-allocated `XplClip`s, each with
+  its own `String`, and then as many `Clip`s again in `compose_xpl_titles`.
+  Unlike the title cap, the cost here is MEMORY rather than drive time:
+  `compose_xpl_titles` de-duplicates by `.evo` name before probing
+  (`seen_evos`), so repeats cost no extra sector reads, but the `Vec`s are
+  built and held regardless. 256 is far above any real disc — a feature is
+  one clip, or two across a layer break; even seamless-branching/multi-angle
+  is tens — and keeps the aggregate bounded at `MAX_XPL_TITLES` x 256 clips
+  rather than the tens of millions above.
+
+- **`MAX_XPL_CHAPTERS_PER_TITLE` (1024)** bounds `<Chapter>` elements per
+  `<Title>` — the same `descendants()` amplification, on the second unbounded
+  `collect()` in the same loop, bounded separately so capping clips doesn't
+  simply move the attack next door. A chapter is a bare `f64` rather than a
+  `String`-carrying struct so it's cheaper, but a
+  `<Chapter titleTimeBegin="…"/>` element is also smaller, so the element
+  count an XPL can reach is comparable. 1024 is far above any real disc: the
+  DVD/HD-DVD authoring convention tops out at 99 chapters per title, a 10x
+  margin.
+
+## scan_hddvd_titles
+
+Scans HD-DVD titles from the `HVDVD_TS/` `.evo` clips. The main feature is
+authored as one or more `.evo` clips (a layer-break split —
+`FEATURE_1`/`FEATURE_2` or `feature`/`feature_Divide`). The `HVA*.VTI`
+navigation file names every clip in authored order; this parses it to
+concatenate the feature clips into ONE title (so the largest-title pick gets
+the whole movie, not just part 1), emitting every other clip as its own
+title. Falls back to one title per clip when the VTI is absent or
+unparseable, so a disc with no readable navigation still enumerates.
+`chapters`/duration are left empty pending deeper VTI parsing.
+
+Cancellation: `halt` is polled once per clip and again before every probe
+chunk, and a read that fails with `Error::Halted` — how a live drive reports
+a Stop, since `Drive::checked_exec` fails every command once its flag is set
+— is propagated rather than swallowed. `Halted` is the only error this
+returns; every other read failure keeps its best-effort behaviour. It has to
+be an error and not a short title list: a cancelled enumeration that
+returned `Ok` would be indistinguishable from a disc that genuinely holds
+fewer titles, and the caller would cache and act on it.
+
+## xpl_depth_within_limit
+
+Rejects a disc-supplied XML blob whose element nesting exceeds
+`MAX_XPL_DEPTH`, BEFORE it reaches the parser. `roxmltree` is
+recursive-descent and its depth-10 limit applies only to ENTITY expansion, so
+element nesting is unbounded: a few hundred KB of well-formed XML (far under
+the read cap) overflows the thread stack. That is a process ABORT, not an
+`Err` and not an unwind, so neither the `Document::parse` fallback nor
+`catch_unwind` can contain it; the only fix is to not hand the document over
+at all. A byte-size cap is deliberately NOT added: file size is already
+bounded by the UDF read path, and a size cap does not close this class (a
+180 KB document already aborts) — depth is the bound that matters.
+
+This is a conservative scan, not a validator: it tracks `<name …>` /
+`</name>` while skipping comments, CDATA, processing instructions and
+declarations, and treats `<… />` as non-nesting. A miscount can only cost a
+pathological document its fast path, and the failure mode is the existing
+one — fall back to the clip-name heuristic.
+
+## Test rationale
+
+Detailed rationale for tests in `src/disc/hddvd.rs`'s `#[cfg(test)]` module,
+kept here so the in-code doc can stay within the internal-comment cap.
+
+**`scan_hddvd_feature_composition_saturates_absurd_disc_declared_sizes`** —
+The SECOND size accumulator. `compose_xpl_titles` sums an XPL's clip sizes;
+this one sums the composed FEATURE title's parts, and it reads the same
+disc-declared `u64` Information Length from the same `clip_extents` map. A
+split feature whose two parts each declare a size near `u64::MAX` overflows
+it exactly as the XPL path did. Nothing reconciles the declared size against
+the extents that back it — here each part declares `u64::MAX` while
+occupying ten sectors — because the allocation descriptor's length field is
+only 32 bits wide, so the disc can always claim more than it holds.
+Mutation: restore `size_bytes += *size` in the feature-composition path and
+this goes red (debug: attempt to add with overflow).
+
+**`scan_hddvd_does_not_compose_a_feature_over_an_unrecorded_part`** — A split
+feature (FEATURE_1 + FEATURE_2) where ONE part carries an unrecorded extent
+must not be composed into a FEATURE title at all. Composing around the
+unusable part is the dangerous outcome: the title would play through as if
+it were the whole movie while silently missing that part's runtime, and its
+size still counts it. The other clips remain available as their own titles
+— refusing the composition is not the same as refusing the disc.
+
+**`scan_hddvd_logs_an_unrecorded_feature_part_with_its_own_code`** — The
+refusal above must also be ACCOUNTED, with the unrecorded extent's own code.
+This warn site carried a hardcoded `code = 6017` literal — in the very file
+whose sibling arm was changed to stop doing exactly that — and nothing
+tested it, so neither the literal nor its absence broke anything. Refusing a
+feature and saying nothing leaves the operator with a disc that scanned
+"fine" and is quietly missing its main title. Mutations: deleting the
+`tracing::warn!` (no event to find); restoring the literal `6017` still
+passes here BY VALUE, which is the point — what is pinned is
+`E_UDF_UNRECORDED_EXTENT`'s value reaching the log, so a renumbering that
+the literal could not follow goes red; logging a neighbouring code (e.g.
+`E_UDF_NO_USABLE_EXTENT`) goes red immediately.
+
+**`scan_hddvd_does_not_compose_a_feature_over_a_part_with_no_usable_extent`**
+— The `Ok`-but-empty twin of the test above, and the one that actually bites
+on an ordinary disc: a feature part whose `file_extents` call SUCCEEDS and
+yields nothing usable — here a zero-byte `FEATURE_2.EVO`, no crafted ICB
+required — must refuse the composition too, and must say so in the log.
+Before this, the empty-`Ok` clip entered neither `clip_extents` nor
+`unusable`, so the `any(|n| unusable.contains(..))` guard missed it and the
+`filter(|n| clip_extents.contains_key(..))` beside it quietly DELETED the
+part: the scan composed a `FEATURE` title out of part one alone, still
+advertising itself as the feature, at rc=0, with no diagnostic anywhere.
+Half a movie presented as a whole one — strictly worse than the `Err` case
+the guard was built for, and reachable without a hostile disc. Mutations
+this catches, all of which the pre-fix code exhibited: dropping the
+`extents.is_empty()` branch entirely (a `FEATURE` title appears with one
+extent); inserting into `clip_extents` anyway (same); marking the clip
+unusable but NOT logging (the log assertion fails — absence of a log is
+itself the defect); logging the neighbouring `E_UDF_UNRECORDED_EXTENT`
+instead of `E_UDF_NO_USABLE_EXTENT` (the code assertion fails, because a
+zero-length file is not an authoring hole and triaging the two together
+sends whoever reads it at the wrong population).
+
+**`parse_xpl_titles_caps_a_playlist_declaring_absurdly_many_titles`** — A
+disc-supplied playlist nested far deeper than any real one must be REFUSED
+BEFORE the XML parser sees it. `roxmltree` is recursive-descent and its
+depth-10 limit covers only ENTITY expansion, so unbounded element nesting
+blows the thread stack — an ABORT, which no `catch_unwind` and no `Err`
+fallback can contain. ~50k levels is a few hundred KB of well-formed XML,
+far under the read cap. The correct outcome is the same as any other
+unusable playlist: an empty `Vec`, so the caller falls back to the clip-name
+heuristic. Separately, this test also exercises BREADTH, not depth: a flat
+playlist passes the nesting guard trivially and can still declare a title
+per ~51 bytes, so a 64 MiB XPL (exactly `udf::MAX_FILE_BYTES`) reaches ~1.3
+million of them. The cost is drive time, not memory: `compose_xpl_titles`
+runs `probe_evo_streams` once per title and each probe reads real sectors,
+so an uncapped count turns a scan the operator expects to take seconds into
+tens of terabytes of optical reads. `bluray.rs` is not exposed to this
+because its playlist count comes from the MPLS files present in the UDF
+directory; an XPL DECLARES its titles, so nothing bounds them. Mutation:
+delete the `.take(MAX_XPL_TITLES)` and this goes red at the declared count.
+
+**`nested_title_xpl`** — Builds a playlist that nests `nesting` `<Title>`
+elements inside one another and puts `clips` self-closing
+`<PrimaryAudioVideoClip>` elements at the innermost level, plus `chapters`
+`<Chapter>` elements. `parse_xpl_titles` collects a title's clips with
+`descendants()`, not `children()`, so EVERY one of the `nesting` ancestors
+collects the SAME innermost clip list — the amplification this exercises.
+
+**`parse_xpl_titles_caps_clips_per_title_against_descendant_amplification`**
+— CLIPS PER TITLE is the axis the title cap, the depth cap and the
+directory cap all leave open. `MAX_XPL_TITLES` bounds how many titles a
+playlist may declare and `MAX_XPL_DEPTH` bounds how deeply it may nest, but
+NEITHER bounds how many `<PrimaryAudioVideoClip>` elements a single title
+collects. Worse, the collector is `descendants()`, so one clip nested inside
+N ancestor `<Title>`s is collected N times over — the clip count MULTIPLIES
+by the nesting the depth guard still permits. A 64 MiB XPL
+(`udf::MAX_FILE_BYTES`) holds ~1.7M clip elements at ~38 bytes each; with
+the 32 `<Title>` ancestors the depth cap still permits, that is ~56 million
+heap-allocated `XplClip`s, and then as many `Clip`s again in
+`compose_xpl_titles`. This test uses small numbers that exercise the same
+multiplication without a 64 MiB fixture: pre-fix it collected 756 clips per
+title, 18,900 across the 25 nested titles, from a document declaring only
+756 clip elements — an exact 25x, the nesting count. Mutation: delete the
+`clips.len() >= MAX_XPL_CLIPS_PER_TITLE` break and this goes red at the
+unamplified per-title count.
+
+**`parse_xpl_titles_caps_chapters_per_title`** — CHAPTERS PER TITLE is the
+same `descendants()` amplification on the second unbounded `collect()` in
+the same loop. Bounded separately so closing the clip axis does not simply
+move the attack next door. Mutation: delete the
+`.take(MAX_XPL_CHAPTERS_PER_TITLE)` and this goes red at the declared count.
+
+**`parse_xpl_titles_keeps_every_clip_of_a_realistic_title`** — The control: a
+realistic multi-clip title still resolves EVERY one of its clips and
+chapters. `SYNTH_XPL`'s main movie is a layer-break split — two clips on one
+timeline — plus two chapters; losing either to the cap would cost a genuine
+disc half its feature. Mutation: set `MAX_XPL_CLIPS_PER_TITLE` to 1 and this
+goes red.
+
+**`parse_xpl_titles_accepts_real_world_nesting_depth`** — The depth guard
+must not reject real discs. A genuine `VPLST000.XPL` is a handful of levels
+deep; this is the same document the parsing test uses, plus self-closing
+tags, a comment and a processing instruction that the pre-parse scanner has
+to account for without inflating its depth count.
+
+**`scan_hddvd_composes_titles_from_xpl_playlist`** — The authoritative path:
+when a VPLST000.XPL is present, titles come from the playlist — the
+layer-break split (FEATURE_1 + FEATURE_2) is composed into ONE title with
+the real duration, name, chapters, and per-clip title-time offsets — not the
+clip-name heuristic.
+
+**`compose_xpl_titles_saturates_absurd_disc_declared_clip_sizes`** — A
+title's `size_bytes` is a running sum of DISC-DECLARED clip sizes: the `u64`
+UDF File Entry Information Length, which nothing cross-checks against the
+extent list that file actually occupies. Two clips can therefore each
+declare a size near `u64::MAX`. Summed with a plain `+=`, that overflows: a
+panic in a debug build — a crash on untrusted disc content, which this
+library must never do — and a wrap to a small garbage total in release,
+which misreports the title's size while looking entirely normal. Mutation:
+restore `size_bytes += *size` in `compose_xpl_titles` and this goes red
+(debug: attempt to add with overflow).
+
+**`compose_xpl_titles_dedups_repeated_clip_references_by_evo`** — A crafted
+Advanced-Content playlist can name the SAME `.evo` in
+`<PrimaryAudioVideoClip>` many times over (the XML has no fixed element
+count, unlike MPLS's binary PlayItem count). Each repeat must NOT push
+another copy of that clip's extent list onto the title — mirroring
+bluray.rs's `first_ref = seen_clips.insert(...)` gate, which pushes a clip's
+extents only the first time its id is seen. Here the analogous key is the
+`.evo` filename (this file has no clip_id; `.evo` is what `clip_extents` is
+keyed by). Without the gate, extents grows by the referenced clip's full
+extent list on EVERY repetition — unbounded by the number of on-disc files,
+bounded only by playlist size.
+
+**`scan_hddvd_titles_drops_a_split_feature_whose_part_cannot_be_read`** — A
+clip whose extents cannot be resolved must drop the SPLIT FEATURE. Catches
+reverting the `Err(e) => { warn; unusable.insert(..) }` arm in
+`Disc::scan_hddvd_titles` back to the bare `Err(_) => {}` it replaced. RED
+BEFORE GREEN, and TWO earlier attempts at this test did NOT go red. The
+first asserted "no title names the broken clip" — that passes either way,
+because a clip that resolves to no extents is never inserted into
+`clip_extents` and so yields no per-clip title regardless. The second fixed
+that but shipped no `.vti`: `order` is built solely from
+`parse_vti_clip_order` of the navigation file, so with no `.vti` it is
+EMPTY, `feature` is empty, and no composed title is ever built — the
+assertion held vacuously with the fix reverted. Hence the synthetic
+`HVA00001.VTI` fixture: it is what makes the composer run at all. The
+defect lives one level up from the per-clip titles, in the composed
+feature: `unusable` is what tells the composer that a part is MISSING
+rather than merely absent, and the old bare `Err(_) => {}` populated it for
+nothing but an unrecorded extent. So a scratched sector under FEATURE_2's
+ICB (`Error::DiscRead`) left FEATURE_1 composing a title named "FEATURE" by
+itself — half a movie offered as the whole one.
+
+**`scan_hddvd_titles_excludes_a_clip_with_zero_sectors`** — A clip whose
+file has a zero-byte size (a degenerate/empty allocation: its ICB's
+allocation descriptor has `data_len == 0`, the UDF AD-list terminator, so
+`file_extents` yields no extent at all) must not produce a title. NOTE: this
+exercises the *upstream* `data_len == 0` terminator path in
+`crate::udf::UdfFs::file_extents`, not the `sectors > 0 && lba > 0` guard in
+`scan_hddvd_titles` itself — with this fixture (`file_extents` never returns
+a `(lba, 0)` tuple, and `PART_START` unconditionally makes every resolved
+`lba` positive) that guard is unreachable in a divergent way; kept here as a
+regression check on the zero-byte-file behavior in its own right.
+
+**`scan_hddvd_titles_probes_once_for_entries_resolving_to_identical_extents`**
+— THE THIRD AMPLIFICATION AXIS on HD-DVD title composition, past both
+existing guards. `xpl_depth_within_limit` bounds XML NESTING;
+`MAX_XPL_TITLES` + the `.evo` de-dup bound what an XPL can DECLARE. Both
+live on the playlist path — and an attacker simply omits `/ADV_OBJ`, so
+`read_adv_obj_xpl` returns `None` and neither guard is ever consulted.
+Control then reaches the clip-name FALLBACK, which emits one title per
+`.evo` DIRECTORY ENTRY and probes each. Nothing de-duplicates a FID's ICB
+LBA, so every name in a 1 MiB directory (`udf::MAX_DIR_BYTES`, ~24,000 FIDs)
+can point at ONE File Entry. Each resolves to the SAME extents and each
+costs a full `EVO_PROBE_SECTORS` (16 MiB) probe: ~375 GiB of optical reads
+from a directory that describes a single file. Memoizing the probe on the
+resolved extent list collapses that to ONE probe, because all of those
+names resolve to one extent list. Mutation: drop the memo lookup in
+`EvoProbeCache::streams` (always probe) and this goes red at `ENTRIES`
+probes.
+
+**`the_clip_cap_and_probe_budget_bound_a_scans_worst_case_read_volume`** —
+The clip cap and the per-probe read budget are ONE bound, not two, and only
+their product is meaningful: `MAX_HDDVD_CLIPS` probes each cost up to
+`EVO_PROBE_SECTORS`, so the pair fixes the worst-case drive time of a
+`Disc::scan()`. `EvoProbeCache` does not help against a crafted disc here:
+it keys on the RESOLVED extent list, and distinct-but-overlapping extent
+lists all reading one physical region miss the memo every time while every
+read succeeds. So the product is genuinely reachable, and it is the number
+that has to stay within what a scan can absorb. 8 GiB is the ceiling
+asserted here. It is far above any genuine disc — retail HD-DVDs carry tens
+of `.evo` clips, i.e. well under 1 GiB of probing — and far below the 64 GiB
+the pair used to permit, which exceeded the capacity of the dual-layer media
+this format tops out at and took tens of minutes of optical reads. This is
+a relationship, not a magic number: raising EITHER constant without
+re-examining the other trips it.
+
+**`scan_hddvd_titles_still_probes_each_distinct_clip`** — CONTROL:
+memoization must not silently collapse DISTINCT clips. A legitimate disc
+with several different `.evo` files still probes each one, and each title
+keeps the streams of ITS OWN clip. Mutation: make `EvoProbeCache`'s key a
+constant (ignore the extents) and this goes red — the junk clip inherits
+the first clip's H.264 streams.
+
+**`scan_hddvd_titles_caps_a_directory_declaring_absurdly_many_clips`** —
+Memoization alone is NOT the whole fix. Collapsing identical extent lists
+bounds the one-File-Entry attack, but distinct extent lists are only as
+bounded as the File Entries an attacker cares to lay down — and a File
+Entry is ONE sector. A 1 MiB directory's ~24,000 FIDs can each point at
+their own 1-sector File Entry (a ~48 MiB image) declaring its own huge
+extent, so every probe misses the memo and the amplification is back.
+`MAX_HDDVD_CLIPS` is the bound that closes that. Mutation: drop the
+`clips.len() < MAX_HDDVD_CLIPS` gate in the directory scan and this goes
+red at `ENTRIES`.
+
+## EvoProbeCache
+
+`EvoProbeCache` memoizes `probe_evo_streams`, keyed on the RESOLVED extent
+list. Probing is the expensive half of title composition: each pass reads up
+to `EVO_PROBE_SECTORS` (16 MiB) off the medium. Both composition paths can
+reach the same physical clip many times over — an XPL naming one `.evo` from
+many `<Title>`s, or a directory whose FIDs all point at one File Entry — and
+a probe is a pure function of the extents it reads, so the second and later
+passes over an identical extent list are re-reads of bytes already seen. The
+key is the extent list itself, NOT the clip name or title: two names for one
+File Entry share a key (one probe), while two genuinely different clips have
+different `start_lba`s and so keep their own probes and streams. Cache size
+is bounded by the caller's title/clip cap (`MAX_XPL_TITLES` /
+`MAX_HDDVD_CLIPS`).

docs/hevc-mux.md

@@ -0,0 +1,99 @@
+# HEVC Annex B muxer (`src/mux/hevc/mod.rs`) — extended notes
+
+Overflow detail for comments capped by `ci/comment-guard.py`. Each section is
+pointed to from a short `//` comment at the named item.
+
+## Module overview
+
+Writes a raw `.hevc` / `.h265` Annex B byte stream:
+`00 00 00 01 | NAL_unit | 00 00 00 01 | NAL_unit | …` with no container
+framing. On the first frame the muxer emits the codec_private's VPS, SPS, PPS
+(parsed from a `HEVCDecoderConfigurationRecord` in `length-prefixed-in-hvcC`
+form), then converts each PES frame's length-prefixed NAL units to Annex B
+and writes them.
+
+## `write_frame`
+
+Input may be either:
+- Length-prefixed: `[u32-BE len][NAL bytes]` repeated. This is the form
+  emitted by libfreemkv's HEVC parser (the MKV-native layout). Converted to
+  Annex B.
+- Already Annex B: a buffer beginning with a `00 00 00 01` or `00 00 01`
+  start code. Passed through unchanged.
+
+## `hvcc_to_annex_b`
+
+Layout (per ISO/IEC 14496-15 §8.3.3.1.2):
+- 22-byte fixed header
+- byte 22 = `numOfArrays`
+- each array: `array_completeness:1 | reserved:1 | NAL_unit_type:6`,
+  `numNalus:u16-BE`, then `numNalus` × `(nalUnitLength:u16-BE + NAL bytes)`.
+
+We don't filter on NAL type — VPS (32), SPS (33), PPS (34), and any SEI
+arrays included in hvcC all get the same Annex B treatment.
+
+## `length_prefixed_to_annex_b`
+
+Already-Annex-B input (a buffer beginning with a `00 00 00 01` or `00 00 01`
+start code) is detected up front and passed through unchanged — some
+upstream paths (raw HEVC ES from disc) hand Annex B straight through the
+PES layer, and a genuine start code would otherwise be misread as a u32-BE
+length prefix.
+
+Truncation policy (single source of truth across all muxers): if a length
+prefix runs past the end of the buffer (e.g. a NAL truncated by a bad disc
+sector), the truncated trailing NAL is dropped and only the valid Annex-B
+prefix accumulated so far is emitted. We never emit a half-NAL nor leak raw
+length-prefixed bytes into the Annex-B stream.
+
+## `nal_length_size`
+
+Number of octets each NAL length prefix occupies in the elementary data of a
+track described by `record` — the `lengthSizeMinusOne + 1` field of the
+decoder configuration record (ISO/IEC 14496-15).
+
+- avcC (`AVCDecoderConfigurationRecord`, §5.3.3.1.2): byte 4 is
+  `bit(6) reserved | unsigned int(2) lengthSizeMinusOne`.
+- hvcC (`HEVCDecoderConfigurationRecord`, §8.3.3.1.2): byte 21 is
+  `constantFrameRate(2) | numTemporalLayers(3) | temporalIdNested(1) |
+  lengthSizeMinusOne(2)`.
+
+The spec permits only 1, 2 or 4 octets (`lengthSizeMinusOne` of 0, 1 or 3);
+a declared 3 is non-conformant but is decoded rather than rejected, since
+reading N octets is the same operation for every N. A record too short to
+carry the field, or a codec with no such record, falls back to
+`DEFAULT_NAL_LENGTH_SIZE` — the width every freemkv parser emits.
+
+This exists because assuming 4 is silent corruption for a legal source:
+reading a 2-octet-prefixed frame as u32-BE yields an absurd first length,
+the conversion loop bails with nothing parsed, and the raw length-prefixed
+bytes are passed through as though they were already Annex B — a stream
+with no start codes at all, and no error anywhere.
+
+## `append_length_prefixed_as_annex_b`
+
+Same conversion as `length_prefixed_to_annex_b` but writes directly into a
+caller-owned buffer, avoiding an intermediate allocation on hot paths (e.g.
+per-frame video muxing). If `data` doesn't parse as length-prefixed (no
+NALs extracted), it's appended unchanged on the assumption it's already
+Annex B.
+
+## `append_length_prefixed_as_annex_b_sized`
+
+For a source whose NAL length prefixes are `length_size` octets wide rather
+than the 4 this crate's own parsers emit. Derive `length_size` from the
+track's configuration record with `nal_length_size` — ISO/IEC 14496-15 lets
+a legal avcC/hvcC declare 1 or 2 octet prefixes, and reading those as
+u32-BE mangles the frame.
+
+`length_size` outside `1..=4` is clamped to `DEFAULT_NAL_LENGTH_SIZE`; the
+field it comes from is 2 bits wide, so that is unreachable from real input.
+
+## `avcc_to_annex_b`
+
+Layout (per ISO/IEC 14496-15 §5.3.3.1.2):
+- 5-byte fixed header
+- byte 5 = `[reserved:3 | numOfSequenceParameterSets:5]`
+- `numOfSPS` × `(sequenceParameterSetLength:u16-BE + SPS bytes)`
+- 1 byte = `numOfPictureParameterSets`
+- `numOfPPS` × `(pictureParameterSetLength:u16-BE + PPS bytes)`

docs/hevc.md

@@ -0,0 +1,265 @@
+# HEVC parser (`src/mux/codec/hevc.rs`) — extended notes
+
+Overflow detail for comments capped by `ci/comment-guard.py`. Each section is
+pointed to from a short `//` comment at the named item.
+
+## `hevc_num_extra_slice_header_bits`
+
+`num_extra_slice_header_bits` from a HEVC PPS NAL (H.265 §7.3.2.3): after the
+2-byte NAL header, skip `pps_pic_parameter_set_id` + `pps_seq_parameter_set_id`
+(both `ue(v)`) and `dependent_slice_segments_enabled_flag` +
+`output_flag_present_flag` (`u(1)` each), then read `u(3)`. `None` if the PPS
+is too short to parse — the caller then declines to guess a slice type.
+
+## `hevc_first_slice_coding_type`
+
+Measures the coding type from the FIRST coded slice of an access unit
+(H.265 §7.3.6.1 `slice_segment_header`). Reads only the leading fields of the
+first slice segment: `first_slice_segment_in_pic_flag` u(1), the IRAP
+`no_output_of_prior_pics_flag` u(1), `slice_pic_parameter_set_id` ue(v), the
+`num_extra_slice_header_bits` reserved bits, then `slice_type` ue(v). Returns
+`None` for a non-first slice or on truncation — never a guess. `num_extra`
+MUST come from the active PPS so the bit offset to `slice_type` is exact.
+
+## `HevcParser::hdr10`
+
+Combines the accumulated mastering-display and content-light SEI into a
+complete `Hdr10Metadata`, or `None` until BOTH HDR10 SEI messages have been
+seen. Requiring both means an SDR / partially-signalled stream never emits a
+half-populated (confidently-wrong) HDR10 record.
+
+## `HevcParser::scan_sei`
+
+Scans an SEI NAL (`[2-byte NAL header][RBSP]`) for the two HDR10 payload
+types and captures each the FIRST time it appears (per-stream constants).
+
+RBSP structure (Rec. ITU-T H.265 D.2 `sei_rbsp` / `sei_message`): a sequence
+of messages, each `payloadType` then `payloadSize` encoded as a run of 0xFF
+bytes plus a final <0xFF byte (the "ff-extension" coding), followed by
+`payloadSize` payload bytes. Emulation-prevention (00 00 03) is stripped
+before reading — unlike a slice header, an SEI payload can be deep enough
+that an emulation byte falls inside the fields we read. Unknown payload
+types are skipped by their size so a later HDR10 message in the same NAL is
+still reached.
+
+## `HevcParser::mark_clip_boundary`
+
+MPLS `connection_condition` 0x05 and 0x06 are the non-seamless values (per
+the BD-ROM spec: 0x01 = first item / seamless, 0x05/0x06 = non-seamless).
+The first CRA at/after this call is rewritten CRA_NUT (21) → BLA_W_LP (16)
+so a linear decoder sets NoRaslOutput and discards the now-dangling RASL
+leading pictures with no "could not find ref" error.
+
+It is a no-op for the rewrite unless a CRA actually follows: an
+IDR/IDR_W_RADL boundary needs no fix (it carries no cross-splice
+references), and the flag is cleared by the first IRAP-class NAL it reaches.
+
+SAFETY: never call this for connection_condition 0x01 (seamless/first item)
+or within a single-clip title — doing so could convert a legitimate
+mid-content CRA to BLA. The default (never called) path leaves output
+byte-identical.
+
+## `handle_param_set`
+
+Handles a VPS/SPS/PPS NAL: decides whether to strip it (the decoder already
+has the value) or emit it in-band, and tracks the currently-active body.
+
+The decision MUST be made against the currently-active set (`cur`), NOT the
+codecPrivate copy (`first`). The two player behaviours for hvcC-in-MKV
+diverge exactly here:
+
+- A *seek-capable / Annex-B* player (one that converts hvcC to Annex-B by
+  inserting the parameter sets) re-applies the hvcC sets at every keyframe.
+  `reassert_active` handles it.
+- A *streaming* decode (a decoder consuming the MKV directly — what most
+  integrity checkers do) applies hvcC ONCE at init and thereafter updates a
+  parameter set ONLY from an in-band NAL.
+
+So when a title redefines a set mid-stream (id 0 body A → B) and later
+switches BACK to A (== codecPrivate), the change to A must STILL be emitted
+in-band: the streaming decoder is sitting on B and will never revert
+otherwise, decoding the whole A-segment against B → CABAC/cu_qp_delta
+desync. Stripping on `== first` (the old behaviour) dropped exactly that
+revert and corrupted every "switch back to the first body" segment.
+
+Rules:
+- First of its type → seeds codecPrivate; stripped (the decoder gets it from
+  hvcC at init).
+- Equal to the active set `cur` → redundant; stripped.
+- Different from `cur` (a change, in EITHER direction) → emitted in-band and
+  `cur` updated.
+
+Returns `true` when the NAL was emitted in-band into `frame_data`.
+
+## `reassert_active`
+
+Appends the active parameter set `cur` to `prefix` (length-prefixed) so
+every keyframe is SELF-CONTAINED: it carries the active VPS/SPS/PPS in-band
+ahead of its slices. Skipped only when this access unit ALREADY carried the
+NAL in-band (`emitted` — avoids a duplicate) or no active set exists yet.
+
+Why unconditional (not only when the active set differs from codecPrivate):
+a streaming decoder applies the hvcC param sets once at init, then relies on
+in-band repetition. Some sources stop repeating a param set at later IRAPs
+even though its body is unchanged; if the decoder then drops it (a CRA reset
+or SPS event), nothing re-sends it and every subsequent slice fails with
+"PPS id out of range" until the next genuine change (observed as a ~24 min
+corrupt band on one dual-layer UHD title). Re-asserting the active set at
+EVERY keyframe — what compliant Matroska muxers do at every IRAP — makes
+streaming decode self-healing. Re-sending an identical param set is benign
+(decoders expect it at IRAPs); cost is a few hundred bytes per keyframe.
+This strictly supersets the earlier change-only re-assert, so the
+param-set-revert fix is unaffected.
+
+## `parse_mastering_display`
+
+Parses a Mastering Display Colour Volume SEI payload (Rec. ITU-T H.265
+D.2.28 / semantics D.3.28). Layout — 24 bytes total, all big-endian:
+`display_primaries_x[c]` u(16), `display_primaries_y[c]` u(16) for c=0,1,2
+(SEI primary order is c=0 Green, c=1 Blue, c=2 Red); white_point_x u(16),
+white_point_y u(16); max_display_mastering_luminance u(32);
+min_display_mastering_luminance u(32). Returns `None` if the payload is
+shorter than 24 bytes (malformed → ignored, never partially populated).
+
+## Test notes
+
+**`hevc_hdr10_sei_keeps_the_first_value_and_ignores_later_repeats`** — the
+`scan_sei` match arms are guarded with `self.sei_mastering.is_none()` /
+`self.sei_content_light.is_none()`, so the FIRST mastering-display and
+content-light SEI a title carries wins and later repeats (every AU of a real
+HDR10 stream repeats both) are ignored. Each AU below carries only ONE of
+the two messages, so the whole-scan early return
+(`if self.sei_mastering.is_some() && self.sei_content_light.is_some()`)
+never fires early and the per-arm guards are actually exercised.
+
+**`sei_nal` (test helper)** — wraps one or more SEI messages in a prefix-SEI
+NAL (type 39) preceded by an Annex-B start code. The assembled message bytes
+are emulation-prevented (as a conforming encoder would) so they never form a
+false start code; the 0x80 RBSP trailing-bits byte is appended.
+
+**`scan_sei_stops_copying_once_both_hdr10_messages_are_captured`** — MEASURED,
+not reasoned: an HDR10 stream carries a prefix SEI per access unit, and
+`scan_sei` used to allocate + byte-copy the whole SEI RBSP through
+`strip_emulation_prevention` on EVERY one, including after both HDR10
+messages were already captured. On a ~200,000-frame UHD title that is
+~200,000 wasted allocations/copies. Counted at the single
+`strip_emulation_prevention` call site.
+
+**`nonzero_num_extra_slice_header_bits_shifts_the_slice_type_offset`** —
+`num_extra_slice_header_bits` (H.265 §7.3.2.3) is a PPS field, and the
+`slice_reserved_flag[i]` bits it counts sit BETWEEN
+`slice_pic_parameter_set_id` and `slice_type` in the slice segment header
+(§7.3.6.1). Every earlier fixture used a PPS with the field == 0, so the
+skip was never exercised: a parser that ignored the field entirely agreed
+with all of them, and would then read `slice_type` from the wrong bit offset
+on any real stream that sets it — mislabelling every picture's coding type.
+
+**`reasserts_active_pps_at_bare_keyframe`** — regression (UHD banded
+corruption): a stream redefines PPS id 0 mid-title, then a later keyframe
+arrives WITHOUT repeating it (the source relies on the decoder retaining the
+redefinition — valid for a raw bitstream). An hvcC player re-applies the
+FIRST (codecPrivate) PPS at every keyframe, so the active redefinition must
+be re-asserted in-band at that bare keyframe or the whole segment decodes
+against the wrong parameter set.
+
+**`keyframe_param_reassert_does_not_reallocate_the_frame`** — MEASURED: the
+keyframe parameter-set re-assert must be spliced into the front of the
+already-assembled access unit IN PLACE, not built as a fresh full-size
+buffer. It used to `prefix.extend_from_slice(&frame_data)` and then replace
+`frame_data` with `prefix`, which grew a few-hundred-byte `prefix` to the
+FULL access-unit size — a fresh multi-MB allocation — memcpy'd the whole
+frame into it, and dropped the presized buffer. One extra whole-frame
+allocation plus one extra whole-frame copy per keyframe: a 2 h UHD title at
+24 fps with a 1 s GOP is ~7,200 keyframes, ~14-28 GB of avoidable memcpy per
+title. `PARAM_REASSERT_HEADROOM` exists so the splice never reallocates;
+this test counts the reallocations that happen, which must be zero.
+
+**`emits_switch_back_to_codecprivate_pps`** — regression (a UHD title, the
+real bug): id 0 is body A (→ hvcC), then redefined to B, then the title
+switches BACK to A. A streaming decoder (hvcC at init, in-band updates only)
+is sitting on B; the switch back to A must be emitted IN-BAND even though A
+== codecPrivate, or the whole A-segment decodes against B (cu_qp_delta
+desync). Stripping on `== hvcC` dropped this revert.
+
+**`cra_at_auto_detected_pts_backstep_rewritten_to_bla`** — regression for a
+UHD Dolby Vision profile 7 dual-layer title: a multi-clip title is read as
+one concatenated stream and the mpls connection_condition is never plumbed
+to the parser, so the splice CRA opening the next clip kept its dangling
+RASL leading pictures and a linear decoder flooded "Could not find ref with
+POC N". The parser must AUTO-DETECT the boundary from the backward PES-PTS
+reset between clips (each .m2ts has its own PTS base) and rewrite that
+splice CRA → BLA_W_LP with no explicit `mark_clip_boundary` call.
+
+**`cra_after_33bit_pts_wrap_not_rewritten`** — regression for the 33-bit PTS
+wraparound false-trigger (rc.5.2 audit #1): a SINGLE clip whose raw 90 kHz
+PES PTS crosses the 2^33 counter wrap (~26.5 h) must NOT be mistaken for a
+non-seamless clip join. Before the fix the raw 2^33→0 backward step armed
+`pending_clip_boundary` and the next in-clip CRA was wrongly rewritten
+CRA→BLA_W_LP (dropping valid RASL pictures — visible corruption). After
+unwrapping onto a monotonic timeline the wrap is absorbed and the CRA stays
+CRA.
+
+**`cra_splice_detected_at_large_pts_magnitude_not_masked_by_wrap_logic`** —
+the wrap-vs-backstep test above keeps `high_pts` near the very top of the
+33-bit range, close enough to the `PTS_WRAP_PERIOD / 2` threshold that
+`high - unwrapped` and a hand-flipped `high + unwrapped` land on the SAME
+side of the threshold at every step — it doesn't actually distinguish the
+two. This test uses PTS magnitudes around 3e9 (order 2^32, well below the
+wrap threshold but reached in well under an hour), where the subtraction and
+the addition diverge: ordinary forward progression keeps `high - unwrapped`
+small, but `high + unwrapped` would already exceed `PTS_WRAP_PERIOD / 2` on
+the very next frame, which would pollute `pts_wrap_offset` by a full period
+and mask the genuine two-clip splice that follows.
+
+**`non_cra_nals_never_rewritten_at_boundary`** — non-CRA NALs are never
+rewritten even when a boundary IS marked. IDR (19), RASL (8/9), VPS/SPS/PPS,
+and a trailing slice all pass through unmodified; the IDR clears the pending
+boundary so no later CRA is wrongly converted.
+
+**`no_boundary_marker_is_byte_identical`** — a frame stream with NO boundary
+marker is BYTE-IDENTICAL to a parser that has no splice-rewrite field at all
+(the UHD-safety guarantee): asserts byte-equality of every emitted frame
+across a multi-AU stream containing CRAs, IDRs, RASLs, VPS/SPS/PPS, and
+trailing slices — none of which is ever marked.
+
+**`seamless_boundary_no_rewrite`** — a SEAMLESS boundary (connection_condition
+0x05/0x06) is expressed by NOT calling `mark_clip_boundary`, so a CRA across
+a seamless join is left unchanged. This encodes the contract: only
+non-seamless joins call `mark_clip_boundary`; seamless ones never do, so no
+rewrite occurs.
+
+**`redefined_pps_emitted_inline`** — a parameter set REDEFINED mid-stream
+(same id, different body) must be emitted INLINE so the decoder
+re-activates it. Some discs redefine PPS id 0 partway through the title;
+the old parser kept only the first PPS, so the second segment decoded
+against the wrong PPS (CABAC desync).
+
+**`make_sps_full` (test helper)** — builds a stored SPS NAL with sub-layers
+and a conformance window, so the parser must skip sub-layer PTL and the 4
+conformance-window ue(v) fields before reaching the bit depths.
+`max_sub_layers_minus1` controls the sub-layer loop.
+
+**`hvcc_array_length_round_trips_above_256_bytes`** — the hvcC array length
+is a 16-bit big-endian field written as two separate `push`es: `(len >> 8)
+as u8` then `len as u8`. Every VPS/SPS/PPS the rest of the suite feeds is
+well under 256 bytes, so the high byte is always 0 and a `>>` -> `<<`
+mutation (which also always truncates to 0 for those inputs) is
+unobservable there. A real HEVC SPS with an extended VUI/HRD block can
+exceed 256 bytes, so this test uses 300+ byte VPS/SPS/PPS and decodes the
+16-bit length fields back to confirm they round-trip to the exact NAL
+length, not merely a byte that happens to be 0.
+
+**`hevc_ps_reorder_is_installed_and_flush_drains_its_real_frames`** — HEVC
+counterpart of `h264_ps_reorder_reconstructs_distinct_display_pts`. A
+DVD/HD-DVD program stream stamps a PTS only on each GOP anchor, so the
+parser must reconstruct display-order timestamps for the rest. Two things
+are pinned here that nothing else constrains: `with_ps_reorder(true)` must
+actually INSTALL the reorderer (a builder that returned a
+default-constructed parser would silently leave the transport-stream path
+in place on every DVD title), and `flush()` must drain the reorderer's real
+buffered frames at EOF — not nothing, and not a manufactured empty frame at
+PTS 0 (a zero-length Block whose timestamp jumps back behind every cluster
+already written, RFC 9559 §5.1.3.2). Slice bodies follow H.265 §7.3.6.1:
+`first_slice_segment_in_pic_flag`, the IRAP-only
+`no_output_of_prior_pics_flag`, `ue(pps_id)`, `ue(slice_type)` (Table 7-7:
+0 = B, 1 = P, 2 = I). PPS body 0xC0 sets `num_extra_slice_header_bits = 0`.

docs/hex.md

@@ -0,0 +1,26 @@
+# hex
+
+The single hex → bytes parser for the whole workspace.
+
+## Why one parser
+
+Key material arrives as hex from three third-party sources — the keydb, an
+online key service, and the mapfile's `# freemkv-vid:` comment — and each
+used to parse it slightly differently (one stripped `0x`/`0X`, one stripped
+nothing, one stripped `0x` only). A key written with a prefix one parser
+didn't expect was silently dropped → "can't decrypt" with no error. This is
+the one parser they all call, so the prefix/case/validation rules live in
+exactly one place.
+
+## Byte-oriented, not char-oriented
+
+Operates on BYTES, not `&str` char indices: the inputs are untrusted, so a
+multi-byte UTF-8 scalar must reject as malformed, never panic on a
+mid-codepoint slice.
+
+## `byte()` internals
+
+Combines two ASCII hex-digit bytes into one byte. `as char` is intentional:
+for a non-ASCII byte it produces a Latin-1 scalar that `to_digit(16)` then
+rejects — so non-hex (incl. `+`/`-` sign chars) and multi-byte input fail
+cleanly rather than slipping through `from_str_radix`'s sign handling.

docs/identity.md

@@ -0,0 +1,75 @@
+# identity.rs — drive identity test notes
+
+## `OversizedCountTransport` (test double)
+
+Returns the requested data length but reports a `bytes_transferred` larger
+than the caller's buffer — models a drive that lies about its transfer
+count. The old slicing code panicked on this; the clamps in `from_drive`
+must keep it from indexing out of range.
+
+## `inquiry_with_a_short_data_phase_fails_instead_of_reporting_a_blank_drive`
+
+`ascii_field` with a buffer shorter than `start` returns empty string
+rather than panicking.
+
+- Spec: SPC-4 §6.4.2 — bytes[8:16] are vendor ID; a truncated buffer (e.g.
+  a device that reports fewer than 8 bytes) must not panic.
+- Mutation: removing the `data.len() > start` guard makes it panic on
+  short inputs.
+
+A drive that answers INQUIRY with GOOD status but a short or empty data
+phase must fail the probe, not present as a blank drive.
+
+The buffer is pre-zeroed, so decoding it unconditionally yielded empty
+vendor/product/revision strings and a byte 0 of 0x00. Every platform
+enumerator gates on `raw_inquiry[0] & 0x1F == SCSI_PERIPHERAL_TYPE_OPTICAL`,
+and 0x00 is DIRECT ACCESS — so the drive silently vanished from the device
+list rather than reporting that its identity probe failed. A USB-SATA
+bridge mid-wedge does exactly this.
+
+The two GET CONFIGURATION calls in the same function already clamped on
+`bytes_transferred`, with a comment calling it untrusted; INQUIRY, three
+lines above them, discarded it.
+
+## `ascii_field_boundary_len_equals_start_is_empty`
+
+`ascii_field`'s guard is `data.len() > start` (strictly greater), not
+`>=`: a buffer whose length is exactly `start` has NO byte at that offset,
+so it must still yield empty, not attempt to slice.
+
+Mutation: `>` -> `>=` would try to slice `data[start..]` when
+`data.len() == start`, which panics (empty range at the very end is fine,
+but the guard's job is the `< start` case below it — pinning the exact
+boundary catches an off-by-one either direction).
+
+## `display_formats_trimmed_fields_space_separated`
+
+`Display` renders the four trimmed identity fields space-separated — the
+human-readable counterpart of `match_key`'s pipe-separated form. Not
+exercised anywhere else in this test module.
+
+Mutation: replacing the `fmt` body with `Ok(Default::default())` writes
+nothing at all, so formatting any `DriveId` yields "".
+
+## `FixedGcCountTransport` (test double) / `from_drive_gc_failure_yields_empty_firmware_date`
+
+GET CONFIGURATION failure (transport error) must not abort the identity
+probe — firmware_date is empty, raw_gc_010c is empty. Mutation:
+propagating the GET_CONFIGURATION error with `?` aborts `from_drive`.
+
+`FixedGcCountTransport` is a transport whose GET CONFIGURATION responses
+report an exact, caller-chosen `bytes_transferred` for each of the two GC
+features (010Ch firmware date / 0108h serial), so the `end > 12` / `> 12`
+boundary guards can be pinned precisely. INQUIRY always succeeds.
+
+## `from_drive_firmware_date_boundary_exactly_12_is_empty`
+
+`end > 12` in the firmware-date branch (`from_drive`) is a strict
+inequality: `bytes_transferred == 12` reports the field absent (offset 12
+is the first byte of the 12-char date; a count of exactly 12 covers bytes
+0..12, none of which is the date), so `firmware_date` must be empty, not
+the mutant's off-by-one read.
+
+Mutation: `>` -> `>=` would try `gc[12..12]` at the boundary — an empty
+but non-panicking slice — silently reporting "present" data that is
+actually all outside the transferred count.

docs/ifo.md

@@ -0,0 +1,168 @@
+# IFO parser notes
+
+Overflow rationale relocated from `src/ifo.rs` comments (see `// See docs/ifo.md`
+pointers in that file for the anchor point of each section below).
+
+## `DvdTitle::feature_start_cell` (Bug-4: scene-selection/logo at head of feature)
+
+The main feature's PGC can open with leading cells that are NOT part of the
+movie — a scene-index segment or an interleaved-angle sub-block. This walks
+the leading run and returns the index of the first cell that is a plain
+feature cell (category `0x00`-class).
+
+Conservative by construction — it can NEVER truncate a normal feature:
+- It only ever skips a *prefix*; the scan stops at the first plain-feature
+  cell and keeps everything from there on.
+- A normal single-angle feature has category `0x00` on cell 0, so the scan
+  stops immediately at index 0 and drops nothing.
+- It never drops on duration or any heuristic — only on the spec category
+  bits — and it never drops the FIRST cell of an angle block (the angle we
+  keep).
+- As a final guard it never returns past the last cell, and never drops when
+  that would leave zero cells.
+
+For a real disc where every feature cell category is `0x00` and chapter 1
+sits at 00:00:00, this returns 0 — a no-op — which is the correct result: the
+disc's scene-index lives in a separate menu/title PGC, not in leading cells
+of the feature PGC, so there is nothing to drop here.
+
+## `bcd_to_frames` / `bcd_to_secs` (dvd_time_t is a timecode, not wall-clock time)
+
+Format: `[hours_bcd, minutes_bcd, seconds_bcd, rate_and_frames]`
+  - Byte 0: hours in BCD (e.g. 0x01 = 1 hour, 0x12 = 12 hours)
+  - Byte 1: minutes in BCD
+  - Byte 2: seconds in BCD
+  - Byte 3: bits 7-6 = frame rate flag (01=25fps, 11=29.97fps),
+    bits 5-0 = frame count in BCD
+
+The seconds field advances once every [`DvdRate::nominal_fps`] frames. On
+NTSC discs that is every 30 frames, but 30 frames of 30000/1001 fps video
+last 1001/1000 s — so reading H:M:S as literal seconds under-reports real
+time by exactly 0.1% (3.6 s per hour). Callers that need real seconds must go
+through the frame count, which is what `bcd_to_secs` does.
+
+## `MAX_TT_SRPT_TITLES` / `parse_tt_srpt`
+
+DVD-Video caps a disc at 99 titles (VMGI TT_SRPT `TT_Ns`, and the 99-title /
+99-title-set structure the format is built around), but the on-disc count is
+an untrusted `u16`: a ~800 KB crafted IFO can declare 65535 entries, each
+re-parsing a PGC into a full `DvdTitle` (~540 MB of `DvdInfo`). Headroom: this
+IS the format maximum, so it clips no conformant disc — a real DVD cannot
+address a 100th title through TT_SRPT.
+
+`parse_tt_srpt` has two bounds on untrusted input: the declared entry count
+is clamped to `MAX_TT_SRPT_TITLES`, and entries naming a `(vts_number,
+vts_title_num)` pair already seen are dropped. De-duplication is a
+correctness fix as well as a bound: two TT_SRPT entries pointing at the same
+VTS title are the same title, and `parse_pgcit` would otherwise re-parse
+that one PGC into a separate `DvdTitle` per entry.
+
+## `parse_audio_attr` visibility
+
+`pub(crate)` for the CROSS-MODULE tests only. The sole production caller is
+`parse_vts_attributes` in this file; `src/mux/mkv.rs`'s `#[cfg(test)]` block
+calls it directly so its language-mapping tests run the real parser over real
+on-disc IFO bytes end to end, instead of a hand-built `DvdAudioAttr` that
+could agree with the muxer while both disagree with the disc. Narrowing this
+would mean either a `#[cfg(test)]`/`#[cfg(not(test))]` pair of signatures
+that can drift apart, or moving those tests away from the code they exist to
+pin — both worse than the widened crate-internal visibility, which reaches no
+public API.
+
+## `assign_audio_sub_stream_ids`
+
+On DVD-Video the sub-id's low nibble is the audio-stream *number* (0-7),
+shared across all codecs — the single stream index the PGC `audio_control`
+table / navigation registers select — and the high nibble is the codec base.
+So the sub-id is `codec_base | position`, where `position` is the stream's
+index in the IFO audio-attribute table (NOT a per-codec running count):
+  - AC-3  → `0x80 | i`
+  - DTS   → `0x88 | i`
+  - LPCM  → `0xA0 | i`
+  - MP1/MP2 and anything else → `None` (regular MPEG-audio PES, not a
+    private-stream-1 sub-id).
+
+A per-codec ordinal was wrong: it only coincides with the wire id when a
+codec's first stream is also the disc's audio stream #0. Any codec that is
+not the first audio stream (e.g. a DTS track after an AC-3 track) then got
+a sub-id one-too-low, so the demux routing key (`0xBD00 | sub_id`) never
+matched and the track muxed silent. The positional index is the real wire
+number, so distinct positions still give distinct sub-ids (no collision).
+
+Position saturates at 7 so a malformed over-count never produces an
+out-of-range sub-id.
+
+## `parse_raw_dvd_lang_bytes`
+
+The salvage is deliberately not narrowed to a-z: whatever survives is only
+ever a lookup key for `dvd_lang_to_iso639_2`, which degrades anything it does
+not recognize to `und`, so a stray `X` or `5` costs nothing and cannot reach
+an output stream as a language code.
+
+## `dvd_lang_to_iso639_2`
+
+Uses `labels::vocab::iso639_1_to_iso639_2`, which spans the WHOLE of ISO
+639-1 (plus the withdrawn spellings `iw`/`in`/`ji` that DVD-Video's
+frozen-1988 language list still puts on disc). The narrower `vocab::menu_lang`
+table is deliberately NOT used here: it exists for Blu-ray menu-graphic
+filename tokens and knows only 25 languages, so a Region-2 disc's Romanian,
+Bulgarian, Croatian, Serbian, Slovak, Slovenian, Hebrew, Estonian, Latvian,
+Lithuanian and Icelandic tracks would all fold onto `und` together. DVD
+streams carry an empty `label`, so the language is the only thing
+distinguishing one subtitle track from the next — a valid code that is
+identical for six tracks is worse for the user than the invalid one it
+replaced. Both tables normalize to ISO 639-2/T, so they agree wherever they
+overlap.
+
+An empty or unrecognized code degrades to `"und"` (ISO 639-2 / Matroska's own
+"undetermined" value) — a valid element value — rather than passing through
+an invalid 2-letter code or an empty string. Never guesses.
+
+## `video_attr_absolute_bytes_pin_real_layout` test
+
+ABSOLUTE-BYTE pin (audit §3 #2): the existing video-attr tests build the byte
+via `v_atr_byte(...)`, which uses the SAME shift constants the parser reads
+with — a co-edit of constant + helper would silently re-introduce the
+PAL-as-NTSC bug and every test would still pass. This test feeds
+`parse_video_attr` HARDCODED bytes captured from real DVD-Video layouts
+(DVD-Video video attributes: mpeg_version[7-6] video_format[5-4]
+display_aspect[3-2] permitted_df[1-0]) — no `v_atr_byte`. If the parser's bit
+positions drift, these fail.
+
+## `dts_after_ac3_uses_positional_substream_id` test
+
+Regression (The Punisher 2004): audio[0]=AC-3 5.1, audio[1]=DTS 5.0. The DTS
+track sits at audio position 1, so its wire sub-id is 0x89 (0x88 | 1), NOT
+the per-codec 0x88. With the old per-codec ordinal it got 0x88 → demux
+routing key 0xBD88 had no match → every DTS packet (which carries 0x89) was
+dropped → the track muxed present-but-silent while the AC-3 (at position 0,
+where ordinal and position coincide) played fine. Positional numbering fixes
+it end-to-end.
+
+## `pgc_chapter_times_ntsc_no_pulldown_drift` test
+
+Regression test for issue freemkv#25 (NTSC chapter drift). Builds a PGC from
+the real cell table of the disc in the bug report and checks the chapter
+marks against the reference tool's values. Before the fix, chapter 14 landed
+4.019 s early; the drift was proportional to elapsed time (0.1%), so a short
+synthetic fixture would not have caught it.
+
+## Test additions note
+
+The block of tests starting at `cell_category_low_flags_are_bit_isolated`
+covers cell-category bit isolation, palette/program-map arithmetic, and the
+malformed-language salvage paths.
+
+## `build_pgc` test fixture
+
+Builds a standalone PGC starting at offset 0. Layout: 0xEA-byte header, then
+the program map (one byte per program, the 1-based first cell number), then
+the 24-byte cell playback table. `cells` are `(category, BCD time,
+first_sector, last_sector)`.
+
+## `build_pgcit` test fixture
+
+Builds a VTS_PGCIT at offset 0: VTS_PGC_Ns(2) + reserved(2) +
+VTS_PGCIT_EA(4), then one 8-byte VTS_PGCI_SRP per PGC (VTS_PGC_CAT(4) +
+VTS_PGCI_SA(4), the PGC's byte offset from the VTS_PGCIT start). `pgcs` are
+appended after the SRP table.

docs/image-writer.md

@@ -0,0 +1,35 @@
+# `src/io/image_writer.rs`
+
+## Why this is not `freemkv_engine::copy`
+
+The engine's `copy` is the RECOVERY path — mapfile sidecar, `--multipass`
+sweep/patch, damage-jump, ECC-aware batching, auto-resume. Every one of those
+exists because an optical drive returns read errors on marginal media. A
+file-backed or synthesized source has no marginal media: a read either
+succeeds or the underlying file is broken, and retrying it is pointless.
+
+Routing a non-drive source through the recovery path is not merely wasteful,
+it is wrong. Its mapfile identity check compares AACS unit keys and the VID,
+both of which are empty for an already-decrypted source, so identity passes
+for ANY such source: a second run with a different input to the same output
+path would resume over the previous image and produce wrong content at exit
+zero. Keeping the two paths separate makes that unrepresentable.
+
+So: drive sources get `freemkv_engine::copy`. Everything else gets this.
+
+## `write_image` rationale
+
+The output is a faithful image of whatever the source presents — decrypted
+if the caller wrapped the source in a
+[`DecryptingSectorSource`](../src/sector/decrypting.rs), ciphertext if it did
+not. `write_image` performs no decryption itself and makes no decryption
+decision; that belongs to the caller, which knows whether the run is
+`--raw`.
+
+On cancellation the partial file is left in place — the caller decides
+whether a partial image is worth keeping, and deleting a multi-gigabyte file
+the user may want to inspect is not this function's call to make.
+
+A short read from the source is treated as an error rather than zero-filled:
+silently padding a truncated source would produce an image that looks
+complete and is not.

docs/index-bdmv.md

@@ -0,0 +1,10 @@
+# `/BDMV/index.bdmv` layout
+
+Binary layout of the BD navigation index (First Play, Top Menu, and the
+title table), as parsed by `src/bdnav/index.rs`.
+
+`"INDX"` + version(4) + `indexes_start`(u32 @8) + … ; at `indexes_start`:
+`index_len`(u32), First-Play object(12), Top-Menu object(12),
+`num_titles`(u16), then `num_titles` title objects(12 each). Every object's
+`object_type` is the top two bits of its first byte; for an HDMV object the
+`id_ref` into `MovieObject.bdmv` is a big-endian u16 at object offset 6.

docs/index-select.md

@@ -0,0 +1,7 @@
+# FMTS index selection
+
+Where the resolved index comes from is a separate concern from disposition
+classification (`resolve_disc_index` in `src/aacs/index_select.rs`): today it
+is read off the index keys the key source handed us; when Processing Keys are
+available it will come from the VK derivation instead. Either way the
+disposition logic in `unit_disposition` is identical.

docs/inf.md

@@ -0,0 +1,100 @@
+# `aacs::inf` — notes
+
+## `UnitKeyFile`'s hand-written `Debug`
+
+Redacting `Debug`, per the policy `aacs::types` documents: this struct holds
+the disc's ENCRYPTED CPS unit keys — exactly the material a keydb entry stores
+— plus the disc hash they are looked up by. A derived `Debug` printed every key
+byte verbatim, so any `{:?}` (a downstream crate, an `assert_eq!` failure
+message, a future `tracing::debug!` in this module) leaked them. Only
+non-secret shape is printed. Guarded by `unit_key_file_debug_is_redacted`.
+
+The disc hash is the public keydb lookup key, printed as hex the same way
+`DiscEntry` prints its own — never as raw bytes.
+
+## `parse_vtkf`
+
+Layout — AACS "HD DVD and DVD Pre-recorded Book" Table 3-8, a fixed
+2480-byte file, verified byte-exact against real discs (Freedom `VTKF090`,
+Dukes of Hazzard `VTKF000`):
+```text
+  [0x00..0x0C] magic "DVD_HD_V_TKF"
+  [0x0C..0x10] BE32 HD_VTKF_SIZE (2480)
+  [0x10..0x1C] associated playlist name ("VPLST%%%.XPL")
+  [0x1C..0x80] reserved
+  [0x80..]     64 entries × 36 bytes:
+                 BIFO (1) | reserved (3) | ENCRYPTED title key (16) | binding MAC (16)
+                 BIFO bit 7 (AV_FLG) set = this slot holds a title key
+                 (pre-recorded discs fill the binding MAC with 0xFF)
+  [0x9A0..2480] 16-byte TKF MAC (CMAC keyed by Kvu — NOT a key)
+```
+The slot index (1-based) is the CPS unit number, so an absent slot is
+SKIPPED (not a terminator) — collapsing gaps would renumber later keys and
+hand the wrong title key to CPS unit N+1. The title→CPS mapping is
+playlist-driven (`VPLST%%%.XPL`) and owned by the HD DVD enumerator, so
+`title_cps_unit` is left empty here.
+
+The prior parser used a 32-byte stride (a 12-byte pad instead of the 16-byte
+binding MAC). That reads entry #1 correctly but drifts +4 bytes per entry
+after it, so it only decrypted single-CPS-unit discs; every multi-key VTKF
+(real multi-CPS-unit HD-DVD titles) yielded garbage keys for CPS unit ≥2.
+
+## `synth_vtkf` test helper
+
+Build a synthetic `VTKF%%%.AACS` matching the real on-disc layout (AACS
+HD DVD Book Table 3-8, verified against Freedom `VTKF090` and Dukes
+`VTKF000`): magic, BE32 size, playlist name, reserved to 0x80, then 64
+entry slots of 36 bytes (the first `keys.len()` present with `AV_FLG`
+set, the rest empty), a reserved gap, and the 16-byte trailing TKF MAC.
+
+## `unit_key_file_debug_is_redacted` test
+
+`UnitKeyFile` holds the disc's ENCRYPTED CPS unit keys. A derived `Debug`
+printed every byte; the hand-written impl must not. Sentinel key byte
+0xD5 = decimal 213 (a derived `Debug` renders `[u8; 16]` in decimal), the
+same probe `aacs::types::redaction_tests` uses. Mutation guard: putting
+`#[derive(Debug)]` back fails this.
+
+## `read_mkb_from_drive_returns_the_concatenated_pack_payload` test
+
+`read_mkb_from_drive` is the in-drive MKB source: every AACS derivation
+downstream (`mkb_find_mk_dv`, the subset-difference walk, the whole
+Media Key ladder) consumes exactly what it returns. An empty return is
+not a benign "no MKB" — it is a total read failure reported as success,
+and every derivation then fails with a key-not-found code that points
+the operator at their keydb rather than at the drive.
+
+This pins the CONTENT: the concatenated payload of all packs, in pack
+order, byte for byte.
+
+## `read_mkb_from_drive_issues_the_exact_mmc_cdb_for_each_pack` test
+
+The CDB is what the drive actually acts on, and every byte of it is
+load-bearing: a wrong format code returns a different disc structure
+entirely, and a wrong allocation length truncates the pack. The existing
+test above pins the opcode, the format code and the pack number; this
+pins the WHOLE 12-byte CDB, so no field can drift unnoticed.
+
+Expected layout (MMC-6 READ DISC STRUCTURE, AACS MKB format):
+`[0]` opcode, `[1]` media type 0x01, `[2..6]` address = pack number
+(BE32), `[6]` layer 0, `[7]` format 0x83, `[8..10]` allocation length
+BE16 = 32772 = `0x80 0x04`, `[10..12]` reserved/control.
+
+## `read_mkb_from_drive_accepts_a_full_size_pack` test
+
+A pack payload filling the FULL 32768-byte window must come back whole.
+The `len > 0 && len <= 32768` bound is what stands between a maximal
+pack and a silently dropped one, and the small payloads used elsewhere
+in this module never reach it.
+
+## `read_mkb_from_drive_ignores_a_pack_declaring_more_than_the_buffer_holds` test
+
+A drive that DECLARES more payload than it returned must not be
+believed. The BE16 length in the response header is drive-supplied data:
+a firmware bug, a short transfer, or a hostile device can put a value in
+it that runs past the 32772-byte buffer. Copying `len` bytes on that word
+alone panics the rip thread mid-scan.
+
+Both the first-pack read and the per-pack loop carry the same bound, so
+both are exercised here: the over-declared pack contributes nothing and
+the honest pack still comes through.

docs/io-mod.md

@@ -0,0 +1,34 @@
+# `src/io/mod.rs` — background
+
+## `WritebackFile`
+
+Drop-in wrapper around `std::fs::File` for any call site that performs
+large sequential writes (sweep, patch, mux, etc.). It implements `Write`
+and `Seek` so existing code paths can swap `File` for `WritebackFile`
+with no body changes. Internally it drives a `WritebackPipeline` that,
+on Linux, drains dirty pages continuously at 32 MB granularity to avoid
+the kernel's accumulate-then-burst flush behaviour. macOS and Windows
+use a no-op pipeline — their default cache policies have not been shown
+to exhibit the same pathology for this access pattern.
+
+## `FileSectorSource`
+
+The read-side dual of `WritebackFile` — it implements
+[`crate::sector::SectorSource`] for an ISO file using direct
+`pread`-equivalent calls so the kernel's own readahead policy runs
+(which interleaves naturally with the concurrent writeback). It pairs
+that with periodic `posix_fadvise(DONTNEED)` drops on the consumed
+window so an 85 GB streaming ISO read doesn't fill the page cache and
+starve the concurrent MKV write.
+
+## `Pipeline` + `Sink`
+
+The generic producer/consumer primitive used by sweep, patch, and mux
+to overlap reads with writes via a bounded channel + dedicated consumer
+thread.
+
+## `byte_prefetcher`
+
+The read-ahead producer feeding the mux pipeline for `io::Read`-backed
+sources: a worker thread fills a recycled pool of buffers and ships
+them through a channel, exposing `BytePrefetcher` / `PrefetchShell`.

docs/jar.md

@@ -0,0 +1,25 @@
+# src/labels/jar.rs — relocated comment prose
+
+## `MAX_CLASS_BYTES` rationale
+
+A real BD-J `.class` is far under this ceiling (64 MiB); a lying header
+simply gets truncated and the class fails to parse, which is skipped like
+any other bad entry. The buffer is grown incrementally and the read is
+capped here rather than pre-sized from the declared size.
+
+## `for_each_jar` "top-level" vendor examples
+
+"Top-level" means entries directly under `/BDMV/JAR/`, not nested under a
+subdir. Pixelogic, Criterion, Paramount, etc. put their data files inside
+`/BDMV/JAR/<x>/`; dbp and Deluxe put their jar directly at
+`/BDMV/JAR/<name>.jar`.
+
+## `read_is_bounded_by_cap` test rationale
+
+The read is bounded by `MAX_CLASS_BYTES`: a stored entry whose real payload
+exceeds the cap yields only the first `MAX_CLASS_BYTES` bytes to the
+parser, never the full (unbounded) entry. Verified here on a small cap via
+the entry-count path: the truncated bytes still parse a valid class
+prefix, but no read beyond the cap occurs. The test asserts the entry is
+still surfaced exactly once (the cap does not drop legitimate entries) and
+that the call returns.

docs/key-provider.md

@@ -0,0 +1,68 @@
+# KeyProvider (src/aacs/provider.rs)
+
+Long-form notes for `src/aacs/provider.rs`, relocated from doc comments to
+stay under the comment-guard caps. See the module's own (trimmed) `//!` doc
+for the short version.
+
+## Method flavors
+
+`KeyProvider` methods come in two flavors:
+
+- **Bulk material** (`device_keys`, `processing_keys`, `media_keys`) — the
+  resolver unions (and dedups) results across all providers and tries each
+  candidate.
+- **Disc-keyed lookup** (`lookup_disc_by_hash`, `lookup_disc_by_vid`) — the
+  resolver short-circuits on the first hit, so providers are queried in
+  array order with fastest/closest first.
+
+`host_certs` is a sixth method but is NOT consumed by the resolver chain:
+the SCSI handshake reads host certs directly from the caller-supplied
+credentials, not from the provider array. A provider that overrides
+`host_certs` today has no effect on the handshake; the method is retained
+as a forward-looking extension point only. Correspondingly,
+`Providers::host_certs` (the union helper) is `#[allow(dead_code)]` and
+unused by the resolver chain today.
+
+Default impls return empty / `None` so backends only override the methods
+they actually support — an external key service might implement only
+`lookup_disc_by_hash`, while a local file might implement all six.
+
+Calls may block (disk I/O, network round-trips). The resolver invokes each
+method at most a handful of times per scan; for per-disc memoization,
+implementations should cache internally.
+
+## `Providers` (resolver-side aggregation helper)
+
+The resolver wraps `ctx.providers` (`&[&dyn KeyProvider]`) in `Providers`;
+its methods apply the union-vs-short-circuit policy described above per
+method. The bulk unions dedup so overlapping providers don't make the
+resolver re-walk/re-validate identical material.
+
+## `SuppliedKey` (bridge for `Disc::decrypt_with`)
+
+A `KeyProvider` backed by a single caller-supplied key's raw material — the
+bridge for `crate::disc::Disc::decrypt_with`.
+
+The application's key source did the lookup and handed in material at one
+level (DK / PK / MK / VUK). This exposes exactly that material to the
+version-dispatched resolver, which owns ALL derivation — so a source never
+derives, and the lib remains the single home for the AACS chain across
+1.0 / 2.0 / 2.1 / 2.x.
+
+Each level fills only its own field; the rest stay empty, so the resolver
+naturally runs the matching path (DK→…, PK→…, MK-pool brute, or a
+disc-keyed VUK hit). `decrypt_with` already knows the disc, so the
+`lookup_disc_by_*` hash/VID arguments are irrelevant — a present
+`disc_entry` is returned for any query.
+
+## Test: `providers_host_certs_unions_every_providers_certs_in_array_order`
+
+`Providers::host_certs` is the union across the provider array. It is not
+wired into the handshake today (see above), so nothing else in the crate
+would notice a body that dropped every cert on the floor — and the day it
+IS wired in, a silently-empty cert list means the drive AACS authentication
+finds no host certificate to present and every disc fails to open, with no
+indication that the caller's certs were discarded.
+
+Unlike the bulk key unions this one does NOT dedup (`HostCert` is not
+Ord/Hash), so the assertion is on the full concatenation in array order.

docs/keysource.md

@@ -0,0 +1,254 @@
+# keysource.rs — extended notes
+
+Overflow rationale relocated from `src/keysource.rs` doc comments by the
+comment-guard (prose caps: 8 lines for pub-item rustdoc, 3 lines for internal
+comments). Each section below is pointed to by a short `//`/`///` comment at
+the corresponding site in the source.
+
+## Module overview — ownership split
+
+libfreemkv still OWNS the crypto: the boil-down primitives and the AES live
+here. A source owns only PATH ORCHESTRATION — deciding which primitive to
+call with what input for the material it happens to hold. Source
+implementations are published in the companion `freemkv-keysources` crate,
+keeping key *policy* (which store, which order, online vs local) out of the
+library. It knows what material it holds (a DK / MK / VUK / pre-decrypted UK)
+and what it must fetch from the disc (VID, MKB, encrypted title keys, content
+samples) to get there.
+
+## `MIN_SAMPLE_UNITS` — why this many, why here
+
+The key service identifies a key by which of the submitted units it decrypts,
+so too few samples — especially on FMTS, where a segment interleaves several
+variants at the unit level — can return a key that matches an incidental unit
+rather than the one asked about (a false positive). This many distinct units
+make the request unambiguous.
+
+Canonical here (the base crate) so BOTH consumers agree on one value: the
+online source in `freemkv-keysources` (which refuses to send an under-sampled
+request) re-exports it, and libfreemkv's own FMTS forensic query
+([`crate::mux`]) sizes its per-segment batch by it. Layering forbids the
+reverse import (keysources depends on libfreemkv, not vice versa), so the
+value lives at the lower layer both share.
+
+## `DecodeSampleSet` — parse, don't validate
+
+"Parse, don't validate": the only constructor, `DecodeSampleSet::new`, returns
+`None` for an under-sized slice, so an online key request simply *cannot be
+built* from too few samples. The runtime `len() < MIN_SAMPLE_UNITS` check that
+used to live at the request site (and was silently forgotten by an
+under-sampling caller, reading as "key service down") becomes a compile-time
+obligation: a request builder that takes `&DecodeSampleSet` can never receive
+an unchecked `Vec`.
+
+The *count* enforced here is a runtime property of the disc (how many
+encrypted units it yields); the *requested* count is a caller-side
+compile-time constant that callers pin to `MIN_SAMPLE_UNITS` (see e.g.
+autorip's `SAMPLE_UNITS`). Together the two make under-sampling
+unrepresentable at the request boundary.
+
+The wrapped samples are on-disc AACS ciphertext — the same bytes the sibling
+`DiscInputs::samples` redacts as key MATERIAL — so `Debug` is hand-written and
+redacting.
+
+## `DecodeSampleSet`'s hand-written `Debug`
+
+A derived `Debug` dumped every wrapped sample verbatim: a `DecodeSampleSet`
+carries at least `MIN_SAMPLE_UNITS` 6144-byte aligned units (>= 49 KiB, in
+practice multi-MB) of AACS ciphertext plus each unit's clear 16-byte
+derivation seed, so one `tracing::debug!("{set:?}")` on a failed `/decode`
+request — or an `assert_eq!` whose panic message formats it — wrote all of it
+to the log that gets attached to a bug report. Same policy and same shape as
+`DiscInputs`'s impl.
+
+## `DiscInputs`'s hand-written `Debug`
+
+Redacting `Debug`, per the policy `aacs::types` documents (and which
+`aacs::types::Vid` already applies to this very Volume ID). `DiscInputs` is
+public and returned by `crate::Disc::inputs`, so a consumer's
+`tracing::debug!("{inputs:?}")` used to print the Volume ID, the whole
+`Unit_Key_RO.inf` (the encrypted title keys), the entire MKB and every
+ciphertext sample verbatim into a log that ends up attached to a bug report.
+Only non-secret identity and shape (presence, lengths) is printed.
+
+## `DiscInputsCtx::new` — parse-failure policy
+
+A present-but-malformed `unit_key_ro` (truncated / wrong magic / wrong
+stride) parses to an empty key set, so a later `enc_title_keys` returns
+`Ok(&[])` indistinguishably from a disc that legitimately has no title
+keys — the parse failure is swallowed here, not surfaced as an error.
+
+## `KeySource` trait — the two resolve operations
+
+Returning an empty `Vec` means "no key for this disc from this source"; an
+`Err` means the source itself failed (I/O, parse, network). The caller
+(`resolve_and_apply`) tries each source in order and validates the returned
+keys against real ciphertext before committing them, so a wrong key from one
+source transparently falls through to the next.
+
+Two explicit resolve operations, one per key kind — never one overloaded call
+whose meaning depends on how many keys came back:
+* `get_unit_keys` — the disc's base per-CPS-unit Unit Keys (index space =
+  CPS-unit number). The common path for every disc.
+* `get_fmts_indexes` — the AACS 2.1 forensic index keys (index space =
+  forensic index 1..N). Defaults to empty: a source with no forensic material
+  opts out, and only an FMTS disc ever asks.
+
+What each source must do to answer is the source's own business: a keydb keys
+on `disc_hash` and reads no samples; the online source submits the ctx's
+content samples (a base batch for `get_unit_keys`, an index-1 anchor batch
+for `get_fmts_indexes`) to the key service.
+
+## `resolve_and_apply_traced` — one-shot semantics and CPS-unit numbering
+
+One-shot per source: each source's `KeySource::get_unit_keys` is called
+exactly once with a `DiscInputsCtx` over `inputs`. Non-empty Unit Keys are
+mapped to terminal `Key::Unit`s and applied via `crate::Disc::decrypt_with`,
+which validates them against `inputs.samples` and only mutates the disc on
+success — so a wrong/partial key set is rejected and the loop continues.
+
+CPS-unit numbering: a source returns Unit Keys carrying the POSITIONAL index
+from `crate::aacs::derive::decrypt_unit_key`; the library's canonical
+CPS-unit number is `position + 1` (matching
+`crate::aacs::inf::parse_unit_key_ro`'s `(i + 1)`), so the committed
+`AacsState.unit_keys` is byte-identical to the library-resolved path.
+
+The NUMBER itself is not what descramble indexes by — but the ORDER is
+load-bearing, so a source must return its keys in CPS-unit order. Trial
+decrypt-and-check was deliberately deleted (see `crate::decrypt::AacsKeyMap`:
+decryption is driven by the disc's CPS-unit / FMTS-segment structure, "never
+by trial-decrypt-and-check per unit"), and `decrypt_sectors_mapped` indexes
+the committed pool POSITIONALLY — `unit_keys[key_idx].1`, where `key_idx` is
+a POSITION in the Vec a source returned, recorded by
+`resolve_mux_key_map_cached` / `resolve_fmts_key_map`. Return the same keys
+in a different order and every `AacsKeyMap` points at the wrong key: the
+whole title decrypts under a neighbour's key, or a forensic range trips the
+`is_clean` net into `DecryptFailed`. (The doc used to say the number "is
+cosmetic for descramble (the decrypt path strips it and tries every key)",
+which is what the DELETED trial-decrypt path did; the only place that still
+tries every key is `Disc::decrypt_with`'s sample VALIDATION, which does not
+descramble content.)
+
+## `fetch_unit_keys` — the two callers
+
+This is exactly what both paths do — only the samples differ:
+* at disc open, `ctx` carries reachable-content samples → resolves the
+  up-front CPS units (the common one),
+* in the read, on a decrypt miss, `ctx` carries the FAILING unit's ciphertext
+  → resolves the CPS unit that wasn't sampled up front.
+
+Same sources, same call; there is no separate "fetch". Unlike
+`resolve_and_apply` this does not validate/commit to a disc — the read's
+decorator re-decrypts with the returned keys, which is the validation.
+
+## `FetchOutcome` — the error-signal struct
+
+Whether a driver run resolved keys, and — when it did NOT — whether the miss
+was a genuine "no source holds this key" (`errored == false`) or at least one
+source FAILED (`errored == true`, e.g. a network source was unreachable). The
+distinction gates negative-result memoization: an empty-because-absent
+result is safe to cache, an empty-because-a-source-was-down result is
+transient and must NOT be cached (the key may resolve once the source
+recovers).
+
+## `drive_unit_keys`
+
+`fetch_unit_keys` plus the error signal: drive `sources` in order, return the
+first source's non-empty Unit Keys, and flag whether any source that failed
+to answer did so with an `Err` (a source failure) rather than an empty `Ok`
+(genuine absence — see `KeySource::get_unit_keys`).
+
+## `key_fetch` — one builder, memoization policy
+
+One builder, used by every read path (sweep / patch / mux) and every
+consumer (CLI, autorip) — neither application contains the fetch logic, only
+its key-source config. Cheap to clone; build once, clone into each read
+path. `make_sources` is invoked per fetch (the cold path) so the resolver
+stays `Send + Sync` without requiring `KeySource: Send`.
+
+Each operation is memoized per sample-batch fingerprint (keys are disc-level,
+so repeats hit cache). A genuinely-empty reply is cached, but a source
+FAILURE is not — a transient miss (see `FetchOutcome::errored`).
+
+## `read_encrypted_units` — why here, and the CPI selection rule
+
+Lives in the library, not a key-source crate: reading the disc and carving
+AACS units is decryption *mechanism* (unit geometry anchored at each
+extent's `start_lba`), which the library owns. A key source is *handed*
+these bytes via `DiscInputs.samples`; it never reads the disc itself.
+
+"Encrypted" is decided by `crate::aacs::content::aacs_unit_encrypted` — the
+AACS Copy Permission Indicator (CPI) in the top 2 bits of byte 0, the
+spec-correct signal (`buf[0] & 0xc0`). NOT the `is_clean` TS-sync heuristic:
+a unit lacking clean TS syncs does not imply encryption (an FMTS variant
+frame or an odd clear unit can lack syncs yet be unencrypted), and a clear
+unit sent to a key server yields nothing to validate against — the "0
+encrypted units" rejection. A clip opens with clear navigation units
+(PAT/PMT, menus) whose CPI is clear; only CPI-flagged content units are
+collected — probing several points spread across EACH extent so a title
+whose encrypted body starts late (or whose midpoint lands in clear nav)
+still yields samples. CPI is read at each extent's `start_lba`
+(clip-file-anchored), so byte 0 is a real unit start and the flag is
+meaningful.
+
+## Test doc overflow
+
+### `key_source_host_certs_defaults_to_empty`
+Spec: a source holding no cert returns the empty vec; the `mkb` param is
+forward-looking and the default ignores it. Mutation: a default returning a
+non-empty vec would inject phantom certs into the OEM handshake.
+
+### `errored_empty_is_not_cached_and_retries_when_source_recovers`
+A transient source outage must NOT be memoized as a permanent "no key": a
+fingerprint whose first fetch failed because the source errored must be
+re-asked, and once the source recovers the key resolves. Regression guard
+for the negative-result memoization fix — caching the errored empty would
+permanently drop a recoverable unit for the rest of the op.
+
+### `key_fetch_routes_unit_and_fmts_to_distinct_source_methods`
+The two `KeyFetch` operations route to the two DISTINCT trait methods:
+`unit_keys` drives `get_unit_keys`, `fmts_indexes` drives
+`get_fmts_indexes`. A source that returns different keys per method proves
+the seam no longer collapses "1 base key" and "the forensic set" into one
+overloaded call — the operation, not the return length, decides which.
+
+### `read_encrypted_units_finds_scrambled_content_off_the_midpoint`
+#4 regression: encrypted content NOT at the extent midpoint (a
+late-starting feature, or a midpoint landing in clear nav) must still be
+sampled — empty samples make `decrypt_with` skip wrong-key validation. The
+old midpoint-and-forward sampler returned empty; the probe-spread finds the
+early scrambled band.
+
+### `read_encrypted_units_selects_by_cpi_not_ts_sync`
+DISCRIMINATING: selection is by the AACS CPI (byte 0), NOT the TS-sync
+clarity heuristic. Half the units lack TS syncs but are CPI-CLEAR
+(`byte0 & 0xC0 == 0`) — genuinely UNencrypted units that merely lack TS
+syncs; the old sampler collected these and the key server rejected the POST
+as "0 encrypted units". `read_encrypted_units` must skip them and return
+ONLY CPI-flagged units. A regression to selecting by TS-sync clarity would
+collect the CPI-clear units too and fail the `& 0xC0` assertion.
+
+### `disc_inputs_ctx_parses_unit_keys_at_the_version_stride`
+Audit #5 — a DISCRIMINATING test for the version→stride fix. A 2-key
+`Unit_Key_RO.inf` whose SECOND key sits at the V20 (64-byte) offset; a V10
+(48-byte) parse reads a DIFFERENT region. Confirms `DiscInputsCtx` parses at
+the stride for `inputs.version` — a swapped `from_major` branch or a
+hardcoded stride (the exact bug 1.2.0 fixes) would fail this, where the
+prior single-key fixtures passed regardless of stride.
+
+### `disc_inputs_debug_is_redacted`
+`DiscInputs` is public and returned by `Disc::inputs`, so any consumer's
+`tracing::debug!("{inputs:?}")` prints it. A derived `Debug` printed the
+Volume ID (the value `aacs::types::Vid` deliberately renders as
+`Vid(<redacted>)`), the whole `Unit_Key_RO.inf` (the encrypted title keys),
+the entire MKB and every ciphertext sample verbatim. Sentinel byte 0xD5 =
+decimal 213, matching `aacs::types::redaction_tests`. Mutation guard:
+restoring `#[derive(Debug)]` fails this.
+
+### `decode_sample_set_debug_is_redacted`
+`DecodeSampleSet` is public and wraps the SAME on-disc ciphertext the
+sibling `DiscInputs` redacts, so a derived `Debug` dumped >= MIN_SAMPLE_UNITS
+x 6144 bytes of verbatim AACS ciphertext (plus every unit's clear 16-byte
+derivation seed) into any log that formatted it. Sentinel byte 0xD5 =
+decimal 213, matching `aacs::types::redaction_tests` and the `DiscInputs`
+test above. Mutation guard: restoring `#[derive(Debug)]` fails this.

docs/labels-mod.md

@@ -0,0 +1,556 @@
+# src/labels/mod.rs — design notes
+
+Long-form rationale relocated from doc comments per the comment-guard
+audience cap (internal items cap at 3 lines; see `ci/comment-guard.py`).
+
+## `label_at`
+
+The VENDOR label occupying 1-based STN slot `n` of `stream_type`, if any.
+
+Slot lookup is restricted to labels with no `StreamId`, and that
+restriction is the whole point. `stream_number` is not one coordinate
+system, it is two that share a name:
+
+  * on a vendor label it is a slot in the one stream table the config blob
+    describes, which is what this function's callers count against; while
+  * on a derived label it is that stream's slot in *its own* playlist's
+    table, which says nothing about any other playlist's numbering.
+
+Reading a derived label out of a slot lookup therefore answers a question
+about table A with a fact about table B. A label that carries a `StreamId`
+names the stream it describes outright and is bound by that id instead —
+see `apply_labels`.
+
+## `find_anchor`
+
+Find the title the label list is actually describing, for one stream type.
+
+A vendor label list is a single stream table — one playlist's STN slots —
+but it is handed to every title on the disc. When sibling playlists cover
+the same clip with different stream subsets, per-title ordinal numbering
+puts the same label on different physical PIDs in each, and the flags
+contradict each other. The list itself carries no playlist id, but it does
+carry a language per slot, and that sequence is a fingerprint: on the
+corpus, exactly one title's per-type language sequence reproduces the label
+list position for position, and content confirms that title's binding is
+the correct one.
+
+So: the anchor is the title that `anchor_score` admits and that confirms
+the most of the list. `None` means no title matches — the list describes a
+stream table this disc scan cannot see, and nothing may be bound
+authoritatively.
+
+Only VENDOR slots take part. Derived labels (MPLS / CLPI) name their own
+stream and bind directly, so admitting them here would be asking a title to
+agree with a numbering that describes a different playlist — the mistake
+that made this gate a coin flip while the merged list was the only list
+there was.
+
+## `anchor_score`
+
+How strongly this title's stream sequence matches the vendor label list, or
+`None` if the title contradicts it and cannot be the table it describes.
+
+A stream disqualifies the title when the vendor label on its slot states a
+different language. A slot the vendor list does not name constrains nothing:
+under-yield is the normal shape of these blobs — an authoring layer ships
+editorial labels for the streams it considers interesting and leaves the
+rest as bare slots — so a hole is the list's silence, not a disagreement.
+
+The score is how much of the list the title positively CONFIRMS: slots where
+both sides state a language and state the same one. A list that names no
+languages at all scores zero everywhere and the ranking falls through to
+table size, which is what it did before this became a fingerprint.
+
+## `apply_labels`
+
+Apply a pre-extracted set of labels to titles' streams.
+
+Every label either NAMES the stream it describes or it does not, and that
+split — not a slot number — decides how it binds. Four tiers, most certain
+first:
+
+  1. **This title is the anchor.** `find_anchor` identifies the title
+     whose stream table the vendor list is describing, so its slots are the
+     list's own slots and bind directly.
+
+  2. **An anchor proved this PID.** Every slot of the anchor yields a
+     `(clip, PID) -> label` fact, and a PID is the same physical stream in
+     every playlist that plays that clip. Sibling playlists bind through
+     that map, so a vendor label lands on the same elementary stream no
+     matter which playlist enumerates it, and a slot the anchor never showed
+     us is not bound at all.
+
+  3. **The label names this stream.** A derived label carries a
+     `StreamId` read out of the very table the stream itself was built
+     from, so `(clip, PID)` equality is identity, not inference. This is the
+     floor that gives every stream its language and codec.
+
+  4. **Ordinal, language-checked.** A vendor label with no anchor behind it
+     falls back to the 1-based per-type STN slot — but only where tier 3 had
+     nothing to say, and only when the languages do not contradict.
+
+Tier 3 outranking tier 4 is the substance of this ordering: a label that
+states which stream it belongs to beats a guess about which stream it might
+belong to, even when the guess is the richer label. The policy where a title
+cannot be bound confidently is to leave the stream alone: an unlabelled track
+is a much smaller harm than a full-dialogue track wearing `forced`, which
+presents to the user as a duplicate of the track they wanted, and which the
+muxer can only undo on discs that state `forced_on_flag`. A subtitle label
+carries nothing but the qualifier, so an unverifiable one has no upside at
+all to trade against that risk, and the ordinal path applies one only when
+the label and the stream both state a language and it is the same one.
+
+Audio streams update `purpose` + `label` (codec/variant info; never
+English purpose text). Subtitle streams update `qualifier` and the
+`forced` flag.
+
+Extracted from `apply()` so the matching logic is unit-testable without
+needing a SectorSource / UdfFs.
+
+## `merge_mpls_floor`
+
+Merge the MPLS-derived floor into a framework parser's label list.
+
+The two lists do not share a coordinate system, and the merge must not
+pretend they do. A framework `stream_number` is a slot in the one stream
+table the vendor blob describes; an MPLS label's is that stream's slot in
+its own playlist's table. Matching them by number — which is what this
+function used to do — merges by an equality that means nothing, and the
+merged entries then land on whatever stream happens to sit at that ordinal
+in each title.
+
+So nothing is merged BY slot. Every MPLS label whose stream is not already
+named in `framework` is appended, keeping its own `StreamId`, and
+`apply_labels` decides per stream which of the two reaches it: the
+vendor's editorial label where an anchor puts it there, the floor
+everywhere else. Framework labels stay richer and stay ahead — they are
+simply no longer competing for a slot number.
+
+Sorted at the end (vendor slots first, in slot order, then the named
+streams) so callers see a deterministic list.
+
+## `append_clpi_orphans`
+
+Append CLPI ProgramInfo streams that no existing label already names.
+These are "orphan" streams — physically present in the .m2ts per CLPI's
+clip-authoritative view, but no MPLS playlist references them, so the
+framework and the MPLS floor both missed them. Empirically they are
+commentary or alternate-version streams the authoring tool left out of the
+published playlist. Returns the number appended.
+
+Each carries the `(clip, PID)` it was read under, so it binds to that
+stream and to nothing else. It used to be given `stream_number =
+max(existing per type) + 1, +2, …`, an ordinal invented here and shared
+with the slot numbering the vendor list uses — which meant a title with
+more streams than the list had slots could reach an orphan by counting, and
+be labelled from a stream no playlist even plays. There is no ordinal now:
+a stream that is in no playlist is in no title, so an orphan label binds to
+nothing, which is exactly right and is now structural rather than lucky.
+
+## `select_result`
+
+Pick the winning parser result from `results` (built in PARSERS order):
+highest `Confidence` among non-empty results, with the earliest array
+position winning on a tie — matching `extract()`'s strict-`>` first-wins
+scan.
+
+`Iterator::max_by_key` returns the LAST maximal element, so the key is
+`(confidence, Reverse(index))`: among equal-confidence entries the one
+with the smallest index has the largest `Reverse(index)` and is selected,
+i.e. first wins.
+
+## `collect_chapter_summary`
+
+Scan `/BDMV/PLAYLIST/*.mpls`, parse each, return a row per playlist with
+chapter count (entry marks only) and total duration. Sorted by playlist
+filename. Skipped entries (read error, parse error, no marks) silently
+dropped — this is a diagnostic field, not a correctness-critical one.
+
+## `jar_inventory`
+
+List filenames found under any `/BDMV/JAR/<x>/` subdirectory of the disc.
+Deduped, sorted. Returns an empty vec if no JAR dir is present.
+`pub(crate)` so filename-based parsers (e.g. `png_filenames`) can scan
+menu-asset names without a reader.
+
+## `jar_inventory_from`
+
+The body of `jar_inventory`, over the `/BDMV/JAR` children directly, so
+it is unit-testable without a `UdfFs`.
+
+A `BTreeSet`, not `Vec::contains`: the entry names come from the disc's own
+UDF directory records, so both the file count and the name lengths are
+attacker-controlled, and a linear `contains` doing a full `String` compare
+per candidate is quadratic in the number of files. The set also subsumes
+the trailing sort — it yields sorted, deduplicated output directly.
+
+## test: `jar_inventory_dedup_does_not_hang_on_a_hostile_directory`
+
+`jar_inventory` deduplicated with a linear `Vec::contains`, doing a full
+`String` comparison per candidate — quadratic in a file count taken
+straight from the disc's UDF directory records, with attacker-chosen
+name lengths to inflate each comparison.
+
+This is a HANG GUARD, and the name says so: a return to the linear scan
+makes this fixture run for minutes (120 000² / 2 comparisons over a
+180-byte shared prefix), which without the deadline would wedge CI
+rather than fail it. It is not a complexity proof — no assertion here
+can distinguish `BTreeSet` from any other sub-quadratic dedup, and the
+clock-free half of the claim (dedup, sort, directory exclusion) belongs
+to `jar_inventory_dedups_sorts_and_skips_dirs` below.
+
+The deadline is a real margin, unlike the 6x one that made
+`paramount.rs`'s wall-clock test flake under a loaded CI box: measured
+at 0.14 s debug / 0.07 s release against 10 s, so ~70x. A shared CPU
+does not close that; a quadratic dedup does not survive it.
+
+## test: `parsers_registry_order_locked`
+
+Lock the parser roster + order. If someone reorders the array or
+adds/removes a parser, this test forces them to update the expectation
+explicitly. The order is load-bearing: first matching `parse()` wins, so
+reordering changes which parser claims a disc on overlapping detect
+signals.
+
+dbp + deluxe MUST stay at the end (their detect triggers on "any BD-J
+disc"; placing them earlier would short-circuit the stricter parsers
+above them).
+
+## test: `select_result_first_wins_on_tie`
+
+`select_result` must pick the highest-confidence non-empty result and,
+on a confidence tie, the FIRST in array order (regression for the old
+`analyze()` `max_by(...then(Equal))` no-op that picked the LAST).
+
+`extract()` — the path that actually ships — used to re-derive this
+same rule with its own inline `>` scan and had no test at all, so the
+bug this test guards against could have recurred there unnoticed. It
+now calls `select_result`, so this test covers both.
+
+## test: `suppression_is_by_named_stream_not_by_slot_number`
+
+Spec: the merge suppresses a floor entry only when the list already
+NAMES that stream. A framework label occupying the same slot number is
+not the same fact — a vendor slot and a playlist STN slot are different
+coordinate systems — so it suppresses nothing.
+
+This is the merge rule inverted from what it used to be: the old key was
+`(stream_type, stream_number)`, which dropped a floor entry whenever
+some unrelated vendor slot happened to share its number, and kept one
+whenever it did not. Both outcomes were decided by an accident of
+counting.
+
+## test: log-injection guard on playlist-name logging
+
+A playlist name is a raw UDF directory entry — disc-controlled bytes,
+validated no further than a lossy UTF-8 decode. Logging it through
+tracing's `%` (Display) sigil writes those bytes VERBATIM, so a crafted
+`.mpls` filename carrying ANSI escapes or control characters forges
+terminal output and log structure in any consumer rendering the event
+(CWE-117). `?` (Debug) escapes them, and `str`'s Debug is exactly the
+escaping this needs.
+
+`info!` is not covered by the debug/trace-logging exemption: this fires
+on an ordinary rip of an ordinary disc.
+
+Mutation: put `%` back on `playlist` in `apply_labels` and this goes red.
+
+## test: `forced_label_follows_the_pid_not_the_ordinal_across_sibling_playlists`
+
+The cross-playlist mis-binding this module's two-tier binding exists to
+stop, in its measured shape: two playlists cover the identical feature
+clip, one of them enumerates one extra subtitle ahead of the forced
+slots, and the vendor label list describes the shorter of the two.
+Numbering the same list from 1 inside each title puts the `Forced`
+label on a different PID in each — in the longer playlist, on the full
+dialogue track. The user then sees two identical-looking English
+subtitle tracks, one of them wrongly flagged forced.
+
+Binding by the PID an anchored title proved, rather than by ordinal,
+puts `forced` on the same two physical streams in both playlists and
+leaves the extra one alone.
+
+## test: `ordinal_binding_drops_a_subtitle_label_that_contradicts_the_stream_language`
+
+No anchor to work from (nothing on the disc reproduces the label list's
+language sequence), so binding falls back to the STN ordinal — and a
+label that names a different language than the stream it would land on
+is evidence the list is describing some other stream table. Drop it:
+unlabelled beats mislabelled, because the payload here is `forced`.
+
+## test: `generate_video_label_secondary_dolby_vision_el`
+
+Spec: a secondary (dependent-view) video stream with Dolby Vision
+enhancement layer gets the brand string "Dolby Vision EL"; every other
+HDR format on a secondary stream gets no label at all (that wording is a
+CLI concern). Mutation: delete the `HdrFormat::DolbyVision` arm so it
+falls through to the `_ => String::new()` catch-all, losing the brand.
+
+## test: `generate_video_label_480_boundary`
+
+Spec: 480 lines is the SD floor — a stream with height exactly 480 must
+get the "480p"/"480i" token (BD spec height boundary), not fall through
+to the empty-resolution case. Mutation: `h >= 480` -> `h < 480` inverts
+the boundary so a legitimate 480-line stream (h == 480) produces no
+resolution token at all.
+
+## test: `generate_video_label_sdr_produces_no_hdr_token`
+
+Spec: SDR is the unmarked default — it must never appear as a token in
+the generated label (only non-SDR formats get an explicit tag).
+Mutation: delete the `HdrFormat::Sdr` arm so it falls through to
+`_ => parts.push(hdr.name())`, appending a spurious "SDR" token.
+
+## test: `generate_audio_label_atmos_folds_brand`
+
+Spec: the Atmos-aware variant folds "Atmos" into the codec brand name
+for TrueHD/DD+ carriers, distinct from the plain wrapper. Mutation: stub
+the whole function to `String::new()` / a constant literal — either way
+it stops reflecting the codec/channel inputs.
+
+## test: `generate_audio_label_covers_pc_container_codecs`
+
+Spec: every disc-audio codec in the enum has a full marketing name,
+including the lossy PC-container codecs (AAC/MP2/MP3/FLAC/Opus) that
+`generate_audio_label_all_codecs` above doesn't cover. Mutation: delete
+any one of these match arms — the codec falls through to
+`_ => return String::new()`, silently losing its label.
+
+## `codec_hint_consistent`: chained-OR boundary hardening
+
+The family-detection booleans chain `h.contains(..) || ...` synonym
+checks. Each test below isolates ONE clause so a `||` -> `&&` flip there
+changes the verdict.
+
+### `codec_hint_consistent_truehd_space_synonym`
+
+Isolates the `"true hd"` (space form) synonym in `says_truehd`, which
+mutant testing hit at 396:44's `||`. If that `||` is weakened to `&&`,
+"True HD" alone (no "truehd" substring) no longer sets `says_truehd`,
+`names_family` goes false entirely (no other family clause matches), and
+the function takes the "no family named" early-return path — turning a
+should-be-`false` verdict for a mismatched codec into `true`.
+
+### `codec_hint_consistent_ddp_ac3_plus_no_hyphen_synonym`
+
+Isolates the `"ac3+"` (no-hyphen) synonym in `says_ddp` (398:9's `||`).
+A hint matching only this clause must still classify as DD+, not fall
+through to the plain-AC3 `says_ac3` check.
+
+### `codec_hint_consistent_ddp_eac3_synonym`
+
+Isolates the `"eac3"` synonym in `says_ddp` (401:9's `||`), the last
+clause before the chain moves to "digital plus"/"dd+".
+
+### `codec_hint_consistent_lpcm_bare_pcm_synonym`
+
+Isolates the `"pcm"` (no "lpcm") synonym in `says_lpcm` (409:40's `||`).
+A bare "PCM" hint on a non-LPCM stream must still be judged
+inconsistent — if the `||` were `&&`, "PCM" alone would fail to set
+`says_lpcm`, `names_family` would go false, and the function would take
+the "no family named" path, wrongly returning `true` for ANY codec.
+
+### `codec_hint_consistent_names_family_dts_ma_alone`
+
+Isolates the `says_dts_ma || says_dts_hr` disjunction inside the
+`names_family` chain (418:60). A hint that sets `says_dts_ma` alone
+(e.g. "Master Audio", without "hd ma") must still make `names_family`
+true; weakening that `||` to `&&` requires both clauses at once, so
+`names_family` goes false and the function wrongly reports "consistent"
+for a codec the hint never named.
+
+### `codec_hint_consistent_truehd_arm_atmos_alone`
+
+Isolates the `Codec::TrueHd => says_truehd || says_atmos` arm (433:38).
+An Atmos-tagged hint that names a DIFFERENT lossless carrier by name
+(DD+) must still be judged consistent with a TrueHd stream purely on the
+Atmos marker — `||` -> `&&` would require the hint to ALSO say "truehd",
+which an Atmos-only marker doesn't.
+
+### `codec_hint_consistent_dts_arm_not_bypassed`
+
+Spec: `Codec::Dts` is consistent ONLY when the hint's DTS-family
+bookkeeping (`says_dts`) is true, not just because `names_family` is
+true via some other carrier. Mutation: delete the `Codec::Dts =>
+says_dts` arm (438:9) — it falls to `_ => true`, so ANY named family is
+(wrongly) "consistent" with a Dts stream.
+
+### `codec_hint_consistent_lpcm_arm_not_bypassed`
+
+Spec: `Codec::Lpcm` is consistent ONLY when `says_lpcm` is true.
+Mutation: delete the `Codec::Lpcm => says_lpcm` arm (439:9) — same
+bypass-to-`_ => true` failure mode as the Dts arm above.
+
+## test: `slot_lookup_never_returns_a_label_that_names_its_own_stream`
+
+Spec: a label that names its own stream is never reachable through the
+slot lookup, whatever number it carries.
+
+The two numbers are different coordinate systems. A derived label's
+`stream_number` is its slot in ITS OWN playlist's table; the vendor's is
+a slot in the one table the config blob describes. `label_at` answers
+questions about the second, so it must not return the first.
+
+Mutation: drop the `l.stream_id.is_none()` term from `label_at` — the
+derived label at slot 1 is found first and shadows the vendor's.
+
+## test: `the_derived_floor_cannot_veto_the_anchor`
+
+Spec: the derived floor does not vote on which title anchors the vendor
+list — and in particular cannot VETO the title that does.
+
+The vendor list names two subtitle slots, eng then fra, and the feature
+reproduces them. The feature has a third subtitle the vendor said
+nothing about; the merge dropped a derived label into "slot 3", numbered
+in a different playlist's coordinate system, and it says Spanish. Read
+as part of the vendor sequence that is a contradiction, so the feature
+is rejected, no title anchors, and every flag the list carries is lost.
+
+This is the measured cost of a whole-sequence gate without provenance:
+the vendor's own slots stay correctly positioned while the merged ones
+break the sequence between them.
+
+Mutation: drop the `l.stream_id.is_none()` term from `label_at` — the
+derived "spa" is read as vendor slot 3, `anchor_score` returns `None`,
+and there is no anchor.
+
+## test: `the_anchor_is_the_title_that_confirms_most_of_the_list`
+
+Spec: among titles the vendor list admits, the one that CONFIRMS more of
+it wins — a slot where both sides state a language and state the same
+one is evidence; a slot where either is silent is not.
+
+Here the shorter title matches both named slots outright while the
+longer one states no language at all, so it merely fails to contradict.
+Size alone would hand the anchor to the title that proved nothing.
+
+Mutation: rank on `n` alone (drop `score` from the comparison) — the
+three-stream title with no languages wins.
+
+## test: `a_vendor_qualifier_does_not_leak_onto_a_featurettes_own_stream`
+
+Spec: an editorial qualifier the vendor list states for ONE stream table
+does not leak onto a different physical stream in a title that merely
+counts to the same ordinal.
+
+Measured shape: the feature carries eleven subtitles whose first is SDH;
+a dozen featurettes each carry a single English subtitle, on a different
+clip and a different PID. Both are "subtitle number 1", so the ordinal
+fallback put SDH on all of them — and the languages agree, so the
+language gate could not catch it. What separates them is that the
+featurette's stream is named by the derived floor, and a label that
+names a stream outranks a label guessed onto it.
+
+Mutation: move the `by_id` lookup in `resolve` after the ordinal
+fallback — the guess wins again and the featurette is SDH.
+
+## test: `an_anchor_proves_pids_only_for_the_clip_its_table_came_from`
+
+Spec: the anchor proves a `(clip, PID)` fact only for the clip its
+stream table was READ FROM — the first play item — never for every clip
+the anchor happens to play.
+
+`disc::bluray` builds a title's stream list from `play_items[0]`'s STN
+table, and tier 3 fifty lines below says exactly that by keying its
+derived ids on `clip0`. Tier 2's harvest contradicted it: it recorded
+the anchor's slot PIDs against EVERY clip the anchor plays, so a sibling
+playlist that plays a LATER clip of the anchor bound the anchor's
+editorial label onto whatever stream in that clip happens to reuse the
+PID — a different physical stream, in a different clip, whose own
+language says so.
+
+Mutation: harvest over `&title.clips` instead of its first clip — the
+featurette wears the feature's SDH again.
+
+## test: `a_vendor_codec_claim_does_not_follow_the_ordinal_onto_a_bonus_clip`
+
+Spec: a vendor codec/variant claim does not follow the ordinal onto a
+bonus clip that carries a different codec.
+
+Measured shape: the feature's first audio is object audio; a dozen menu
+and bonus titles each carry one plain stereo track. All of them are
+"audio number 1", and the hint names the same codec family as the stream
+it lands on, so the consistency guard passes it through and every bonus
+clip advertises the feature's format.
+
+Mutation: as above — move `by_id` after the ordinal fallback.
+
+## test: `a_title_shorter_than_the_vendor_list_cannot_anchor_it`
+
+Spec: a title whose stream count is smaller than the vendor list's
+highest slot cannot be the table that list describes.
+
+Mutation: drop the `n < extent` term from `find_anchor` — the one-stream
+title becomes eligible, and on a disc where it sorts first it takes the
+anchor away from the title that actually has the slots.
+
+## test: `an_unnamed_slot_does_not_disqualify_a_title`
+
+Spec: a slot the vendor list never names constrains nothing.
+
+These blobs under-yield by design — the authoring layer ships editorial
+labels for the streams it finds interesting and leaves the rest as bare
+slots. Treating a hole as a disagreement rejects the very title the list
+describes. (Before provenance the holes were filled with labels numbered
+in an unrelated coordinate system, so the gate neither rejected nor
+admitted on evidence.)
+
+Mutation: make `anchor_score` return `None` for an unnamed slot — no
+title anchors and the forced flag is never delivered.
+
+## test: `fill_gaps_leaves_order_untouched_when_nothing_added`
+
+Spec: the sort-by-(type, number) pass only runs when the merge actually
+added something (`added > 0`); when MPLS contributed nothing new,
+`framework`'s existing order (however the caller built it) must be left
+untouched. Mutation: `added > 0` -> `added >= 0` is always true, so the
+sort runs unconditionally, silently reordering a framework list that
+wasn't already in (type, number) order even on a no-op merge.
+
+## `build_program_info` / `build_clpi` (test fixtures)
+
+`build_program_info`: builds a CLPI ProgramInfo section for one program
+with the given (pid, stream_coding_info) pairs. Layout mirrors
+`crate::clpi::parse_program_info`'s expectations: length(4) + reserved(1)
++ num_programs(1), then per-program spn(4)+pmt_pid(2)+num_streams(1)
++num_groups(1), then per-stream pid(2)+sci_len(1)+sci.
+
+`build_clpi`: builds a full CLPI byte buffer (HDMV header + ProgramInfo)
+declaring the given (pid, coding_type, lang) streams. `sci` layout
+follows `crate::clpi::parse_program_info`'s per-coding-type match arms:
+PG/IG = coding_type + 3-byte lang; audio (primary or secondary) =
+coding_type + format/rate byte + 3-byte lang.
+
+## test: `orphans_state_no_stn_slot_and_name_their_stream`
+
+(d) An orphan states NO STN slot, and is identified by the stream it was
+read from instead.
+
+This test used to assert the opposite — that orphans continue the slot
+numbering from `max(existing) + 1`. That number was invented here and
+shared with the coordinate system `label_at` counts vendor slots in, so
+a title with more streams of a type than the vendor list had slots could
+reach an orphan by counting and be labelled from a stream no playlist
+plays. An orphan is by definition in no playlist, hence in no title, so
+there is no ordinal to give it.
+
+## `codec_hint_consistent`
+
+Does the parser's `codec_hint` name a codec consistent with the stream's
+actual `codec`? `apply_labels` uses this to keep richer-but-consistent
+hints (e.g. "Dolby Atmos" on a TrueHD stream — Atmos is a TrueHD extension
+the raw spec codec can't express) while rejecting mis-bound ones (e.g.
+"AC-3 2.0" on a TrueHD stream, the shuffled-label bug). Matching is by codec
+FAMILY parsed out of the hint string. "Atmos" with no carrier named is
+treated as compatible with its lossless carriers (TrueHD / E-AC-3). A hint
+naming no recognizable codec family (pure editorial, e.g. "Commentary") is
+consistent — it isn't asserting a codec.
+
+## `generate_audio_label_atmos`
+
+Atmos-aware variant: same codec/channel string as `generate_audio_label`
+with the object-audio marker folded into the codec brand (e.g. "Dolby
+TrueHD Atmos 7.1"). The "Atmos" string lives here in the label layer, not
+in the core parser. Used when a bitstream probe detected an Atmos
+substream and the stream still carries the basic (non-editorial) label.

docs/labels-xml.md

@@ -0,0 +1,26 @@
+# src/labels/xml.rs
+
+Tolerant XML scraping helpers — promoted from two near-duplicate hand-rolls
+in `paramount.rs` (attribute extraction) and `criterion.rs` (tag-text
+extraction).
+
+These are NOT a full XML parser. They handle the subset of XML the BD-J
+authoring tools we've seen actually emit: ASCII tag/attr names, no entity
+references inside label strings, optional XML namespaces. Hardening goals
+over the prior `find("<tag>")` / `find(r#"name=""#)` matchers:
+
+1. **Case-insensitive** tag and attribute names — vendors casing is
+   inconsistent across authoring-tool revisions.
+2. **Namespace-aware** — strip an optional `ns:` prefix so `<ns:playlist>`
+   and `<playlist>` both match.
+3. **Whitespace-tolerant** — multiple/tab/newline characters around `=`
+   between attribute name and value; whitespace inside the opening tag.
+4. **Quote-style tolerant** — both `"value"` and `'value'`.
+5. **Self-closing tag handling** — `<tag />` and `<tag/>` both work;
+   `text()` returns `Some("")` for empty content.
+
+Out of scope (intentionally simple): XML entity decoding (`&amp;`, `&lt;`,
+etc.), CDATA sections, comments, processing instructions, DTD
+declarations. None of the BD-J authored disc data we've observed
+exercises any of those — labels are plain ASCII/Latin-1 in attribute
+values.

docs/lfsr.md

@@ -0,0 +1,166 @@
+# CSS content cipher (`src/css/lfsr.rs`)
+
+## Module overview
+
+The algorithm is the publicly documented CSS stream cipher, described in the
+open CSS cryptanalysis literature. It is implemented here from that public
+description; its constants (see [`super::tables`]) are the cipher's own
+defined values. Nothing in this file is copied or translated from any
+particular CSS software.
+
+The cipher uses two table-driven linear-feedback circuits:
+- **LFSR1** — a 17-bit register (a 9-bit and an 8-bit half seeded from
+  `key[0..2] XOR seed[0..2]`), stepped through `TAB2`/`TAB3`/`TAB5`.
+- **LFSR0** — a 24-bit feedback register (seeded from `key[2..5] XOR
+  seed[2..5]`), stepped through a feedback polynomial and `TAB4`.
+
+Each output byte is the sum-with-carry of the two register outputs. A body
+byte is recovered as `plain = TAB1[cipher] ^ keystream` — a `TAB1`
+substitution of the ciphertext byte followed by an XOR with the keystream
+(so the cipher is deliberately not its own inverse).
+
+## `descramble_sector`
+
+The two feedback registers are seeded **directly** from
+`title_key XOR sector_seed` (bytes `0x54..0x59`) — there is no title-key
+mangling on the content path (that belongs to the disc/title-key hierarchy,
+not the sector cipher). Only the body, bytes `0x80..0x800`, is transformed:
+`body[i] = TAB1[body[i]] ^ (keystream & 0xff)`.
+
+The scramble flag at byte `0x14` (bits 4-5) marks an encrypted sector. This
+routine CLEARS that flag after unscrambling, so a descrambled sector reads as
+`sector[0x14] & 0x30 == 0`; callers and tests use that to tell it from
+ciphertext, and re-running descramble on an already-cleared sector is a no-op
+(the flag guard below skips it). Clearing does not affect the recovered body.
+
+`sector.len() < 2048` (the encrypted region `0x80..0x800` not fully present):
+callers chunk by 2048, so a trailing partial chunk is left untouched. The
+`debug_assert!` flags this misuse in debug/test builds; a DVD sector is
+always exactly 2048 bytes.
+
+## `scramble_sector` (test helper)
+
+Exact inverse of `descramble_sector`: turn a plaintext sector body into
+CSS ciphertext under `title_key`.
+
+Descramble computes `plain = TAB1[cipher] ^ (keystream & 0xff)`, so the
+inverse is `cipher = TAB1_INV[plain ^ (keystream & 0xff)]` with the identical
+keystream. The keystream derivation is the same as `descramble_sector`;
+only the final substitution differs. Bytes `0x80..0x800` are rewritten in
+place; the scramble flag is set to `0x10` so a subsequent descramble runs.
+
+Not on any production read path — it exists so the key-recovery tests (and
+any caller that needs a known CSS-encrypted sector) can build genuine
+ciphertext rather than approximating it.
+
+## Test notes
+
+### `descramble_produces_the_reference_css_vector`
+
+Regression vector: the deterministic output of the CSS content cipher for
+a fixed key/seed/body. The value is generated by this implementation and
+is self-consistent with the scramble/descramble round-trip test — any
+correct CSS descrambler yields the same bytes, since the cipher is
+deterministic. Pins the implementation against accidental change.
+
+key = 42 13 37 BE EF, seed (0x54..0x59) = DE AD BE EF 42, body = 0xAA.
+
+### `css_descramble_inverts_scramble_over_body`
+
+The content cipher is NOT a plain XOR involution (it applies TAB1 to the
+ciphertext: `plain = TAB1[cipher] ^ ks`). The true inverse is
+`scramble_sector`. Scrambling a plaintext body and then descrambling
+with the same key must reproduce the original body exactly.
+
+### `css_tab1_is_permutation`
+
+Verify the structure of TAB1: it is a substitution table used in key
+mangling. Check that no two inputs map to the same output (TAB1 is a
+permutation of 0..255).
+
+### `descramble_treats_high_bits_of_0x14_as_clear`
+
+Only bits 4-5 of byte 0x14 are the CSS scramble flag: the code reads
+`sector[0x14] & 0x30 == 0` (bits 6-7, i.e. 0x40/0x80, are masked out by
+0x30). A sector with 0x14 == 0x40 or 0x80 must therefore be treated as
+UNSCRAMBLED and left byte-for-byte unchanged. This guards against a
+too-wide mask silently "descrambling" (and thus corrupting) clear data.
+
+Grounding: CSS sector header byte 0x14 — copyright/scramble bits live in
+bits 4-5; the masked value 0 means not scrambled.
+Mutation: widen the mask `0x30` to `0x70`/`0xF0` -> 0x40/0x80 would be
+seen as scrambled and the body would change.
+
+### `descramble_triggers_on_either_flag_bit`
+
+Each individual scramble bit (4 and 5) independently marks the sector as
+encrypted: 0x10 and 0x20 must both trigger descrambling.
+
+Grounding: `(0x10 >> 4) & 3 == 1`, `(0x20 >> 4) & 3 == 2` — both nonzero.
+Mutation: change `!= 0` early-return condition to `== 3` -> a sector
+flagged only 0x10 or 0x20 would be skipped and left scrambled.
+
+### `descramble_clear_preserves_high_bits_of_0x14`
+
+After descrambling, ONLY the two scramble bits are cleared (`& 0xCF`);
+bits 6 and 7 of byte 0x14 must be preserved. A sector with 0x14 == 0xF0
+becomes 0xC0 (bits 6,7 kept, bits 4,5 cleared), NOT 0x00.
+
+Grounding: code does `sector[0x14] &= 0xCF`; 0xF0 & 0xCF == 0xC0.
+Mutation: change `&= 0xCF` to `= 0` or `&= 0x0F` -> the preserved high
+bits assert fails.
+
+### `descramble_leaves_header_and_seed_intact`
+
+The encrypted region is exactly bytes 0x80..0x800. Bytes 0x00..0x80 (the
+header) must NOT be modified by the keystream — except byte 0x14 whose
+flag is cleared. In particular the sector-seed bytes 0x54..0x59 (which
+live inside the header) must survive untouched, since the descrambler
+reads them but never writes them.
+
+Grounding: loop is `sector.iter_mut().take(2048).skip(128)` -> indices
+128..2048 only.
+Mutation: change `.skip(128)` to `.skip(0)` -> header bytes (incl. the
+seed) get XORed and this fails.
+
+### `descramble_covers_final_body_byte`
+
+The descrambler must touch the WHOLE body 0x80..0x800, not just a prefix.
+With a constant body and constant key, the keystream is non-degenerate
+enough that the very last sector byte (index 2047) is altered. This guards
+the loop bound `.take(2048)` against an off-by-one that would leave the
+final byte(s) scrambled.
+
+Grounding: encrypted region end is 0x800 == 2048 (exclusive).
+Mutation: change `.take(2048)` to `.take(2047)` -> last byte unchanged,
+assert fires (this body is all-zero so any keystream XOR shows).
+
+### `descramble_processes_the_first_sector_of_an_over_long_buffer`
+
+The length guard is a FLOOR, not a ceiling: `descramble_sector` is a
+no-op below one sector, and processes the FIRST sector of anything at
+least that long (the loop is `.take(2048)`). `css::descramble_sector` is
+a public entry taking `&mut [u8]` of any length, so a caller handing it a
+multi-sector buffer must get its first sector descrambled — a guard that
+rejected over-long buffers would hand that caller its ciphertext back
+unchanged, with the scramble flag cleared as if it had worked.
+
+### `descramble_output_depends_on_title_key`
+
+Descramble is keyed by `title_key XOR seed`: two different title keys
+produce two different bodies for the same scrambled input. A cipher that
+ignored the title key (or mixed it in wrongly) would yield identical
+output — silent wrong-key decryption.
+
+Grounding: per-sector key = title_key[i] ^ sector[0x54+i].
+Mutation: in the `key` array drop the `title_key[i] ^` term -> both keys
+give the same body, assert fires.
+
+### `descramble_output_depends_on_seed`
+
+Descramble is keyed by the sector seed too: same title key, different
+seed -> different body. Pins that bytes 0x54..0x59 actually feed the
+keystream (not just the per-sector XOR key).
+
+Mutation: replace `seed` array reads with a constant -> both seeds give
+the same body, assert fires.

docs/lib-overview.md

@@ -0,0 +1,53 @@
+# libfreemkv Crate Overview
+
+Overflow detail for the `src/lib.rs` crate-level doc comment, which is capped
+by `ci/comment-guard.py`. Pointed to by the `//!` header there.
+
+## Unlocking
+
+Unlocking -- removing bus encryption (firmware unlock, AACS cert handshake,
+CSS bus-auth) -- lives entirely in the `freemkv-unlock` crate; libfreemkv
+consumes it privately and exposes none of it, so clients are oblivious to
+unlockers (just as they are to the SCSI layer).
+
+## Why a live `disc://` can't go through `input()`
+
+A live `disc://` cannot be opened via [`input`] -- it returns
+[`Error::DiscUrlNotDirect`] by design (use `Drive` + `Disc::scan` +
+`DiscStream::new` directly for a live drive). Any file-backed source
+(`iso://`, `m2ts://`) opens through [`input`].
+
+## Architecture
+
+```text
+Drive           -- open, identify, unlock, read sectors
+  ├── ScsiTransport    -- SG_IO (Linux), IOKit (macOS)
+  ├── DriveId          -- INQUIRY + GET_CONFIG identification
+  └── unlock_bridge    -- private seam to the `freemkv-unlock` crate
+                          (firmware / AACS cert / CSS bus-auth unlockers)
+
+Disc                   -- scan titles, streams, AACS state
+  ├── UDF reader       -- Blu-ray UDF 2.50 with metadata partitions
+  ├── MPLS parser      -- playlists → titles + clips + STN streams
+  ├── CLPI parser      -- clip info → EP map → sector extents
+  ├── JAR parser       -- BD-J audio track labels
+  └── AACS             -- encryption: key resolution + content decrypt
+      ├── aacs         -- KEYDB, VUK, MKB, unit decrypt
+      └── host_certs   -- collect host certs (cert handshake lives in freemkv-unlock)
+```
+
+See also `docs/architecture.md` for the fuller design-level writeup.
+
+## AACS Encryption
+
+Disc scanning automatically detects and handles AACS encryption.
+If a KEYDB.cfg is available (via `ScanOptions` or standard paths),
+the library resolves keys and decrypts content transparently.
+
+Supports AACS 1.0 (Blu-ray) and AACS 2.0 (UHD, with fallback).
+
+## Error Codes
+
+All errors are structured with numeric codes. No user-facing English
+text -- applications format their own messages. See `docs/error-codes.md`
+for the full range table.

docs/local-file-sink.md

@@ -0,0 +1,34 @@
+# `LocalFileSink`
+
+`BufWriter<File>`-backed sink for the common local-disk case
+(`src/io/sink/local_file.rs`).
+
+## Buffering
+
+4 MiB internal `BufWriter`. Sized to coalesce the small per-PES writes
+that come out of the muxer into kernel-page-aligned flushes without
+making the buffer big enough to matter for memory pressure on a single
+concurrent rip.
+
+## Seek-flush ordering
+
+`Seek` flushes the underlying `BufWriter` first; otherwise a seek could
+leapfrog buffered data and silently corrupt the file. This is the same
+shape `BufWriter` itself uses when it impls `Seek` in stdlib, and is
+necessary for MKV's seek-back operations (cluster size patch, Cues
+index, segment header backpatch) to land on the right offset.
+
+## Trait wiring
+
+[`SequentialSink`](../src/io/sink/mod.rs) is implemented explicitly
+(not via a blanket impl) so its `finish()` flushes the `BufWriter` and
+`fsync`s the file even when called through a `dyn` trait object;
+`RandomAccessSink` is implemented over the `Seek` impl.
+
+## Construction contract
+
+Construction always opens the file `create + truncate + read + write`.
+`read` is enabled so the same handle can be reused for a verification
+re-read after the mux (the existing `FileSectorSink::create` pattern).
+On Linux, `with_size_hint` additionally calls
+`fallocate(FALLOC_FL_KEEP_SIZE)` to pre-reserve extents.