v1.6.11: bump version (unified release)

docs: neutralize external references and named techniques (opsec)
test: round-3 coverage on platform shim, ld/aacs error paths, css/mt1959 branches
2026-10-07 18:13:11 +00:00 · 2026-08-25 23:16:54 -07:00 · 2026-08-25 22:18:31 -07:00 · 2026-08-25 22:13:19 -07:00 · 2026-08-25 22:08:48 -07:00 · 2026-08-25 21:48:47 -07:00
27 changed files with 5150 additions and 453 deletions
@@ -0,0 +1,63 @@
+version: 2
+
+# Dependency updates land on `dev`, never on `main`.
+#
+# `main` here is a RELEASE POINTER that release.sh moves to each tag. A bot
+# commit on it would put work there that no tag contains, which is exactly the
+# state that aborted the 1.6.2 cascade at the last step -- so pointing
+# Dependabot at main would recreate that failure on a schedule.
+updates:
+  - package-ecosystem: cargo
+    directory: /
+    target-branch: dev
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 5
+    # One PR per week for the routine bumps instead of one per crate. Eight
+    # repos times a handful of crates is a volume nobody reads, and an
+    # unread PR queue is indistinguishable from no updates at all.
+    groups:
+      minor-and-patch:
+        update-types:
+          - minor
+          - patch
+    ignore:
+      # The freemkv crates depend on each other by GIT TAG, re-pinned by
+      # release.sh as part of the release commit. Dependabot cannot see that
+      # cascade, so a PR bumping one of these would fight the release process
+      # and could pin a version whose tag does not exist yet.
+      - dependency-name: freemkv-unlock
+      - dependency-name: libfreemkv
+      - dependency-name: freemkv-keysources
+      - dependency-name: freemkv-i18n
+      - dependency-name: freemkv-engine
+
+  # The workflows are now real infrastructure -- the release cascade, the
+  # cross-platform hash matrix, the disc gate -- so their actions need the same
+  # attention as the crates.
+  - package-ecosystem: github-actions
+    directory: /
+    target-branch: dev
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 5
+    groups:
+      actions:
+        update-types:
+          - minor
+          - patch
+    ignore:
+      # NOT a dependency: `dtolnay/rust-toolchain` is versioned by the RUST
+      # release it installs, and the tag we pin is the toolchain CI is pinned
+      # to on purpose -- precommit.sh runs the same one locally so a lint that
+      # passes on a developer's newer default cannot pass CI by accident.
+      #
+      # Dependabot reads those tags as semver and proposed 1.97.0 -> 1.100.0,
+      # a Rust version that does not exist. Every such PR 404s on toolchain
+      # download across all eight repos, and they regenerate weekly -- eight
+      # permanently-red PRs that promote.yml then has to special-case when it
+      # decides whether dev is green.
+      #
+      # Bumping the toolchain is a deliberate, all-eight-repos change, made by
+      # hand together with precommit.sh. There is nothing here for a bot.
+      - dependency-name: dtolnay/rust-toolchain
@@ -2,10 +2,12 @@ name: CI

 on:
  push:
-    # `dev` is where work lands and where CI must be green. `main` only ever
-    # moves at release time, to the tagged commit, so a push to it is the
-    # release validation run rather than day-to-day feedback.
-    branches: [main, dev]
+    # dev -> qa -> main. `dev` is where work lands and is meant to be pushed
+    # to often: these are the FAST checks, so a mistake surfaces in minutes.
+    # `qa` is the release candidate — it runs these too, plus the expensive
+    # suite in qa.yml. `main` only ever moves at release time, to a tagged
+    # commit that was already green on qa.
+    branches: [main, dev, qa]
  pull_request:

 # freemkv-unlock is the BASE of the whole ecosystem: libfreemkv path-deps it,
@@ -19,11 +21,37 @@ on:
 # NOT used: with no committed lockfile it fails rather than resolves.

 jobs:
+  # 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:
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@v5
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: actions/checkout@v7
+      - uses: dtolnay/rust-toolchain@1.90.0
        with:
          components: clippy, rustfmt
      - uses: Swatinem/rust-cache@v2
@@ -36,8 +64,8 @@ jobs:
  test:
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@v5
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: actions/checkout@v7
+      - uses: dtolnay/rust-toolchain@1.90.0
      - uses: Swatinem/rust-cache@v2
        with:
          shared-key: freemkv-unlock-ci
@@ -46,24 +74,75 @@ jobs:
      # feature nothing compiles is a feature that breaks at release time.
      - run: cargo test --tests --features emulation

+  # Coverage is additive and NON-REQUIRED: it uploads to Codecov but never
+  # gates a merge (fail_ci_if_error is false, and it is not wired into any
+  # release gate). It mirrors the `test` job's environment — same pinned
+  # toolchain, ubuntu-latest, no `if:` so it runs on every branch and PR just
+  # as `test` does. `--locked` is intentionally omitted to match this crate's
+  # policy (Cargo.lock is gitignored; --locked would fail without it).
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: dtolnay/rust-toolchain@1.90.0
+        with:
+          components: llvm-tools-preview
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: freemkv-unlock-coverage
+      - uses: taiki-e/install-action@cargo-llvm-cov
+      - run: cargo llvm-cov --workspace --ignore-run-fail --lcov --output-path lcov.info
+      - uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          files: lcov.info
+          slug: freemkv/freemkv-unlock
+          fail_ci_if_error: false
+
  # The crate ships on macOS and Windows through its consumers, so it has to
  # compile there. Build the tests (not just `cargo check`) — that forces
  # codegen and catches errors in test-only code, which `check` skips.
  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
+    # platform stops being checked before a release -- qa.yml independently
+    # covers macOS and Windows, and the jobs unique to this file (the Intel
+    # macOS build, the Windows release build) run here on qa and main. A push
+    # to dev is meant to be cheap and frequent; waiting on three runner pools
+    # to agree is what a release candidate is for.
+    #
+    # `if` SKIPS the job (it does not queue). A queued job would be far worse
+    # 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.
+    if: github.ref_name == 'qa' || github.ref_name == 'main'
    runs-on: macos-latest
    steps:
-      - uses: actions/checkout@v5
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: actions/checkout@v7
+      - uses: dtolnay/rust-toolchain@1.90.0
      - uses: Swatinem/rust-cache@v2
        with:
          shared-key: freemkv-unlock-ci
      - run: cargo build --tests --all-features

  check-windows:
+    # 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
+    # platform stops being checked before a release -- qa.yml independently
+    # covers macOS and Windows, and the jobs unique to this file (the Intel
+    # macOS build, the Windows release build) run here on qa and main. A push
+    # to dev is meant to be cheap and frequent; waiting on three runner pools
+    # to agree is what a release candidate is for.
+    #
+    # `if` SKIPS the job (it does not queue). A queued job would be far worse
+    # 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.
+    if: github.ref_name == 'qa' || github.ref_name == 'main'
    runs-on: windows-latest
    steps:
-      - uses: actions/checkout@v5
-      - uses: dtolnay/rust-toolchain@1.97.0
+      - uses: actions/checkout@v7
+      - uses: dtolnay/rust-toolchain@1.90.0
      - uses: Swatinem/rust-cache@v2
        with:
          shared-key: freemkv-unlock-ci
@@ -11,7 +11,7 @@ jobs:
  leak-guard:
    runs-on: ubuntu-latest
    steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v7
        with:
          fetch-depth: 0
      - name: Compute commit range
@@ -0,0 +1,118 @@
+name: qa
+
+# ── The qa gate: "is this production worth?" ────────────────────────────────
+#
+# dev -> qa -> main.
+#
+# `dev` is for committing often. ci.yml answers "is it green" in minutes with
+# fmt, clippy and the unit suite, so a mistake surfaces while it is still cheap
+# to fix. `qa` is the release-candidate branch, and THIS workflow is the claim
+# that a commit is production worth: everything expensive that can run without
+# physical media. `main` only ever receives a qa that went green here.
+#
+# Sibling repos are checked out at `qa`, NOT `dev`. A qa run that resolved its
+# dependencies from dev tips would be validating a combination that is not the
+# one being released, which is the exact failure this branch exists to prevent.
+#
+# What this gate CANNOT cover: `disc://` and real `iso://` need physical media,
+# and no hosted runner has an optical drive or the image hoard. Those run on a
+# self-hosted runner (see the media job at the end) and are the one leg that
+# stays on hardware.
+on:
+  push:
+    branches: [qa]
+  workflow_dispatch:
+
+jobs:
+  # ── Name the candidate ────────────────────────────────────────────────
+  #
+  # Every push to `qa` is a release candidate, so every push gets a tag:
+  # v<version>-rc<N>, N incrementing. That is the answer to "which build is on
+  # qa right now, and is it the one I tested?" — a question that otherwise gets
+  # answered from memory.
+  #
+  # This runs FIRST and does not depend on the gates, deliberately. A red
+  # candidate needs a name more than a green one does: "rc3 failed
+  # release-tests on windows" is a sentence you can act on; "qa is red" is not.
+  # Red on qa is a working gate, not an incident — it is the branch saying this
+  # is not production worth yet. Fix on dev, get dev green, push qa again.
+  #
+  # release.yml excludes v*-rc* so a candidate never publishes a release.
+  rc-tag:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+      - name: Stamp the next rc
+        shell: bash
+        run: |
+          set -euo pipefail
+          v=$(sed -n 's/^version = "\(.*\)"/\1/p' Cargo.toml | head -1)
+          [ -n "$v" ] || { echo "no version in Cargo.toml" >&2; exit 1; }
+          # Numeric sort on the rc ordinal: -rc10 must beat -rc9, and a plain
+          # lexical sort gets that backwards from the tenth candidate on.
+          n=$(git tag -l "v$v-rc*" | sed "s|^v$v-rc||" | sort -n | tail -1)
+          tag="v$v-rc$(( ${n:-0} + 1 ))"
+          git tag "$tag"
+          git push origin "$tag"
+          echo "### Candidate \`$tag\`" >> "$GITHUB_STEP_SUMMARY"
+
+  # The debug suite runs on every dev push. Release is a DIFFERENT build:
+  # overflow checks are off, debug_assert! is compiled out, and inlining
+  # 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:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ['ubuntu-latest', 'macos-latest']
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          path: freemkv-unlock
+      - uses: dtolnay/rust-toolchain@1.90.0
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: freemkv-unlock
+      - run: cargo test --release --tests
+        working-directory: freemkv-unlock
+
+  # clippy's output is target-dependent: cfg-gated code only gets linted on
+  # the target it compiles for. Linting solely on the dev machine's host
+  # target is how a lint that CI rejects reaches a push.
+  cross-lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          path: freemkv-unlock
+      - uses: dtolnay/rust-toolchain@1.90.0
+        with:
+          components: clippy
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: freemkv-unlock
+      - run: rustup target add x86_64-unknown-linux-gnu
+      - run: cargo clippy --all-targets --target x86_64-unknown-linux-gnu -- -D warnings
+        working-directory: freemkv-unlock
+
+  # Windows compiles the tests but does not run them, matching the policy
+  # ci.yml already set. The value here is codegen: the #[cfg(windows)] halves
+  # of the SCSI transport and platform layers compile on no other runner, so
+  # without this they are first built at release time.
+  windows-build:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          path: freemkv-unlock
+      - uses: dtolnay/rust-toolchain@1.90.0
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: freemkv-unlock
+      - run: cargo build --release --tests
+        working-directory: freemkv-unlock
@@ -1,5 +1,175 @@
 # Changelog

+## [1.6.11] — 2026-08-26
+
+### Changed
+
+- Version aligned to 1.6.11 for the unified release. No functional changes to
+  this crate; the release was driven by the libfreemkv main-feature selection
+  improvements and the autorip mux-quarantine fix (see the libfreemkv and
+  autorip 1.6.11 notes).
+
+### Added
+
+- Codecov coverage reporting and badge.
+- Substantially expanded unit-test coverage.
+
+## [1.6.10] — 2026-08-23
+
+### Changed
+
+- Version aligned to 1.6.10 for the unified release. No functional changes to
+  this crate; the release was driven by libfreemkv (TrueHD/MLP audio now resyncs
+  to the next major-sync access unit after a source transport-stream
+  discontinuity, instead of splicing post-gap audio mid-stream — fixing
+  decoder-choking seams on discs whose stream carries a continuity-counter gap;
+  see the libfreemkv 1.6.10 notes).
+- MSRV lowered from 1.97 to 1.90. The crate does not use anything newer than
+  1.90 stabilized; CI's pinned toolchain and `rust-version` are updated to
+  match.
+
+## [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
+
+### Changed
+
+- Version aligned to 1.6.7 for the unified release. No functional changes to
+  this crate; the release was driven by autorip (per-webhook event selection,
+  a progress bar per moved artifact, and move-queue / webhook-error fixes —
+  see the autorip 1.6.7 notes).
+
+## [1.6.6] — 2026-08-20
+
+### Changed
+
+- Version aligned to 1.6.6 for the unified release. No functional changes
+  to this crate; the release was driven by autorip (webhooks may now target
+  private/LAN addresses — see the autorip 1.6.6 notes).
+
+## [1.6.5] — 2026-08-20
+
+### Added
+
+- **AACS 2.0 (P-256) drives now complete a live host-certificate
+  handshake.** The elliptic-curve (P-256) authentication path is wired
+  into the cert handshake for real, not left as dead code. A drive is
+  first tried with the AACS 1.0 certificate (a 2.0 drive accepts it for
+  the Volume ID); if the drive refuses it and the supplied host
+  certificate carries AACS 2.0 credentials, the crate falls back to the
+  native P-256 handshake. It is cert-agnostic — it uses whatever the host
+  certificate carries, with no separate feature gate — and a bus fault on
+  the 1.0 attempt short-circuits the fallback so a dead bus is not
+  hammered. The 2.0 path enforces the same chain-of-trust checks as the
+  1.0 path (drive-cert type gate, fatal certificate verification under the
+  real 2.0 Licensing Administrator key, on-curve validation of every
+  attacker-supplied point, and AGID release on every exit). The 2.0
+  certificate byte layout is documented as provisional pending a genuine
+  drive certificate to pin it against; a wrong layout fails closed and
+  never trusts.
+
+### Security
+
+- **A rogue drive or bridge can no longer forge its way to a trusted bus
+  key.** A drive certificate whose type was neither AACS 1.0 nor 2.0 used
+  to skip Licensing Administrator verification yet still have its own key
+  trusted for the bus-key signature check, letting an attacker inject a
+  chosen bus key; unknown cert types are now rejected at the type gate
+  before any key is trusted. ECDSA verification now validates the signer's
+  public key (on-curve, in-field, not the identity point) before use — a
+  key of (0,0) previously collapsed verification to a forgeable form. The
+  compiled-in AACS 1.0 and 2.0 Licensing Administrator anchor keys, which
+  were off-curve, are replaced with the real published keys (both
+  confirmed on-curve; the 1.0 key verifies a genuine LA-signed
+  certificate). The P-256 certificate-length check now matches the real
+  132-byte layout, so AACS 2.0 certificates verify at all.
+
+- **Sensitive material no longer leaks through debug output.** `Unlocked`
+  (which carries the bus key and Volume ID) and `DriveProfile` (which
+  carries the MediaTek drive firmware image and per-drive vendor SCSI
+  templates) now use hand-written redacting `Debug` implementations
+  instead of printing everything. The AACS 2.0 authentication path now
+  releases the drive AGID on every failure exit, matching the 1.0 path.
+
+### Fixed
+
+- **A dead or failing drive bus is no longer reported as a successful
+  unlock.** A transport fault during the AACS data-key read, during
+  firmware-unlock disc probing, and in both MediaTek speed-probe passes
+  used to be swallowed or flattened into a generic failure — in the
+  firmware-unlock case surfacing as `drive_unlocked: true` on a bus that
+  had actually died. These paths now abort with a transport error so the
+  fault is visible instead of masquerading as clear content.
+
+- **Transport faults are no longer misclassified as "wrong drive" or
+  "bad credentials."** A dead bus on the first probe command previously
+  read as "not a Renesas drive" or "not a supported DVD profile"; a bus
+  that died mid-handshake was reported as a credentials rejection after
+  three retries against dead hardware; and CSS bus-auth collapsed every
+  fault into a generic auth failure. Each call site now honours the
+  transport contract — abort on a real bus fault, fall through only on a
+  genuine "not applicable." A merely short probe response is no longer
+  fabricated into a transport failure, so rips that would have succeeded
+  are no longer aborted.
+
+- **A half-unlocked drive now falls through to certificate
+  authentication instead of claiming the bus is clear.** The firmware
+  unlocker set `drive_unlocked: true` whenever the handshake merely
+  completed, ignoring the computed unlock flag; a drive returning zero
+  bytes could even report a full unlock from a buffer it never wrote.
+  The unlock outcome is now actually consulted, so a partial unlock
+  correctly steers to the cert-auth fallback. Related read paths that
+  parsed the caller's own zero-filled buffer as drive data on a CHECK
+  CONDITION are fixed to inspect status and bytes transferred.
+
+### Changed
+
+- **Drive preparation issues 88 fewer SCSI commands per disc.** The
+  probe's two passes previously walked the same 88 addresses twice; the
+  redundant pass is removed.
+
+## [1.6.4] — 2026-08-15
+
+### Changed
+
+- **No functional change.** This crate ships alongside the rest of freemkv at a
+  matching version; its behaviour is untouched.
+
+## [1.6.3] — 2026-08-10
+
+### Changed
+
+- **Housekeeping only — nothing about how a drive is unlocked has changed.** The
+  cryptography and compression crates this crate builds on were moved to their
+  current releases and brought into line with the versions the rest of freemkv
+  uses, so one version of each is built instead of two.
+
+## [1.6.2] — 2026-08-08
+
+Version sync with the workspace. No functional change in this crate.
+
+## [1.6.1] — 2026-08-07
+
+Version sync with the workspace. No functional change in this crate.
+
 ## [1.6.0] — 2026-08-03

 Version sync with the workspace. No functional change in this crate.
@@ -0,0 +1,18 @@
+# Contributing
+
+Thanks for your interest!
+
+- **Report a bug** — open an issue
+- **Fix a bug** — fork, branch, PR
+- **Suggest a feature** — open an issue first
+
+## Development
+
+```bash
+cargo build
+cargo test
+```
+
+## License
+
+MIT
@@ -1,8 +1,8 @@
 [package]
 name = "freemkv-unlock"
-version = "1.6.0"
+version = "1.6.11"
 edition = "2024"
-rust-version = "1.97"
+rust-version = "1.90"
 license = "MIT"
 description = "Unlock layer for the freemkv toolchain: the Unlocker contract + self-contained firmware/AACS/CSS unlocker modules. libfreemkv depends on this and dispatches via all_unlockers()."
 repository = "https://github.com/freemkv/freemkv-unlock"
@@ -18,11 +18,11 @@ emulation = []
 [dependencies]
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
-base64 = "0.22.1"
+base64 = "0.23"
 tracing = "0.1"
-num-bigint = "0.4"
+num-bigint = "0.5"
 num-traits = "0.2"
 sha1 = "0.10"
-sha2 = "0.10"
-aes = "0.8"
-rand = "0.8"
+sha2 = "0.11"
+aes = "0.9"
+rand = "0.10"
@@ -1,3 +1,7 @@
+[![License: MIT](https://img.shields.io/badge/license-MIT-blue)](LICENSE)
+[![CI](https://github.com/freemkv/freemkv-unlock/actions/workflows/ci.yml/badge.svg)](https://github.com/freemkv/freemkv-unlock/actions/workflows/ci.yml)
+[![codecov](https://codecov.io/gh/freemkv/freemkv-unlock/branch/dev/graph/badge.svg)](https://codecov.io/gh/freemkv/freemkv-unlock)
+
 # freemkv-unlock

 The unlock layer for the freemkv toolchain.
@@ -0,0 +1,22 @@
+# Security Policy
+
+## Supported versions
+
+| Version | Supported |
+| ------- | --------- |
+| 1.6.x   | Yes       |
+| < 1.6   | No        |
+
+Only the current 1.6.x line receives security fixes.
+
+## Reporting a vulnerability
+
+Report vulnerabilities privately through GitHub Security Advisories:
+https://github.com/freemkv/freemkv-unlock/security/advisories/new
+
+Do not open a public issue for a security report. Include the affected
+version, steps to reproduce, and the impact you believe the issue has.
+
+## Response time
+
+You will get an initial response within 7 days.
@@ -0,0 +1,16 @@
+coverage:
+  status:
+    project:
+      default:
+        informational: true
+    patch:
+      default:
+        informational: true
+
+comment: false
+
+ignore:
+  - "tests"
+  - "**/tests"
+  - "benches"
+  - "examples"
@@ -25,6 +25,15 @@ pub enum Error {
    AacsVidRead,
    HandshakeRejected,
    VidUnavailable,
+    /// A handshake step returned FEWER bytes than the protocol step requires.
+    /// The buffer the step would have parsed is the caller's own zero fill, so
+    /// consuming it would turn a failed command into a "successful" handshake
+    /// step built entirely out of zeros.
+    ShortTransfer {
+        opcode: u8,
+        expected: usize,
+        got: usize,
+    },
    /// A SCSI command failed. `status == SCSI_STATUS_TRANSPORT_FAILURE` with
    /// `sense: None` is a transport-layer fault; a CHECK CONDITION carries the
    /// parsed [`ScsiSense`].
@@ -54,6 +63,7 @@ impl Error {
            Error::AacsVidRead => 7012,
            Error::HandshakeRejected => 7013,
            Error::VidUnavailable => 7014,
+            Error::ShortTransfer { .. } => 7015,
            Error::Scsi { .. } => 7099,
        }
    }
@@ -86,3 +96,144 @@ impl From<crate::scsi::ScsiError> for Error {
        }
    }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Every variant has its own stable numeric code. Constructing all 16
+    /// arms also exercises the `#[allow(dead_code)]` variants that the
+    /// wired handshake path never builds.
+    #[test]
+    fn code_is_stable_per_variant() {
+        assert_eq!(Error::AacsAgidAlloc.code(), 7001);
+        assert_eq!(Error::AacsCertRead.code(), 7002);
+        assert_eq!(Error::AacsCertRejected.code(), 7003);
+        assert_eq!(Error::AacsCertShort.code(), 7004);
+        assert_eq!(Error::AacsCertVerify.code(), 7005);
+        assert_eq!(Error::AacsDataKey.code(), 7006);
+        assert_eq!(Error::AacsKeyRead.code(), 7007);
+        assert_eq!(Error::AacsKeyRejected.code(), 7008);
+        assert_eq!(Error::AacsKeyVerify.code(), 7009);
+        assert_eq!(Error::AacsNoKeys.code(), 7010);
+        assert_eq!(Error::AacsVidMac.code(), 7011);
+        assert_eq!(Error::AacsVidRead.code(), 7012);
+        assert_eq!(Error::HandshakeRejected.code(), 7013);
+        assert_eq!(Error::VidUnavailable.code(), 7014);
+        assert_eq!(
+            Error::ShortTransfer {
+                opcode: 0xA4,
+                expected: 16,
+                got: 4,
+            }
+            .code(),
+            7015
+        );
+        assert_eq!(
+            Error::Scsi {
+                opcode: 0xA4,
+                status: 0x02,
+                sense: None,
+            }
+            .code(),
+            7099
+        );
+    }
+
+    /// `scsi_sense` returns the parsed sense for a `Scsi` error carrying one,
+    /// `None` when the `Scsi` error has none, and `None` for every non-`Scsi`
+    /// variant.
+    #[test]
+    fn scsi_sense_returns_the_parsed_sense_only_for_scsi_variant() {
+        let sense = ScsiSense {
+            sense_key: 0x05,
+            asc: 0x20,
+            ascq: 0x00,
+        };
+        let with_sense = Error::Scsi {
+            opcode: 0xA4,
+            status: 0x02,
+            sense: Some(sense),
+        };
+        let sc = with_sense.scsi_sense().unwrap();
+        assert_eq!(sc.sense_key, sense.sense_key);
+        assert_eq!(sc.asc, sense.asc);
+        assert_eq!(sc.ascq, sense.ascq);
+
+        let without_sense = Error::Scsi {
+            opcode: 0xA4,
+            status: 0xFF,
+            sense: None,
+        };
+        assert!(without_sense.scsi_sense().is_none());
+
+        assert!(Error::AacsNoKeys.scsi_sense().is_none());
+    }
+
+    /// `is_scsi_transport_failure` is true only for a `Scsi` error with the
+    /// transport-failure status AND no sense; a drive CHECK CONDITION and
+    /// every non-`Scsi` variant are false.
+    #[test]
+    fn is_scsi_transport_failure_true_and_false_paths() {
+        let transport = Error::Scsi {
+            opcode: 0,
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: None,
+        };
+        assert!(transport.is_scsi_transport_failure());
+
+        let check_condition = Error::Scsi {
+            opcode: 0xA4,
+            status: 0x02,
+            sense: Some(ScsiSense {
+                sense_key: 0x05,
+                asc: 0x20,
+                ascq: 0x00,
+            }),
+        };
+        assert!(!check_condition.is_scsi_transport_failure());
+
+        assert!(!Error::AacsNoKeys.is_scsi_transport_failure());
+    }
+
+    /// `From<ScsiError>` maps a raw transport-layer error into `Error::Scsi`,
+    /// parsing the sense buffer when present and leaving it `None` otherwise.
+    #[test]
+    fn from_scsi_error_maps_status_and_parses_sense() {
+        let e = Error::from(crate::scsi::ScsiError {
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: None,
+        });
+        match e {
+            Error::Scsi {
+                opcode,
+                status,
+                sense,
+            } => {
+                assert_eq!(opcode, 0);
+                assert_eq!(status, SCSI_STATUS_TRANSPORT_FAILURE);
+                assert!(sense.is_none());
+            }
+            _ => panic!("expected Error::Scsi"),
+        }
+
+        let mut buf = [0u8; 32];
+        buf[2] = 0x05;
+        buf[12] = 0x24;
+        buf[13] = 0x01;
+        let e = Error::from(crate::scsi::ScsiError {
+            status: 0x02,
+            sense: Some(buf),
+        });
+        match e {
+            Error::Scsi { status, sense, .. } => {
+                assert_eq!(status, 0x02);
+                let s = sense.expect("sense parsed");
+                assert_eq!(s.sense_key, 0x05);
+                assert_eq!(s.asc, 0x24);
+                assert_eq!(s.ascq, 0x01);
+            }
+            _ => panic!("expected Error::Scsi"),
+        }
+    }
+}
@@ -9,7 +9,7 @@ mod error;
 mod handshake;

 use aes::Aes128;
-use aes::cipher::{BlockDecrypt, KeyInit, generic_array::GenericArray};
+use aes::cipher::{Array, BlockCipherDecrypt, KeyInit};

 use crate::scsi::ScsiTransport;
 use crate::{DiscKind, UnlockCtx, UnlockError, Unlocked, Unlocker};
@@ -17,8 +17,8 @@ use crate::{DiscKind, UnlockCtx, UnlockError, Unlocked, Unlocker};
 /// AES-128-ECB decrypt a single 16-byte block — used to decrypt the bus key /
 /// read_data_key the drive returns after the handshake.
 pub(crate) fn aes_ecb_decrypt(key: &[u8; 16], data: &[u8; 16]) -> [u8; 16] {
-    let cipher = Aes128::new(GenericArray::from_slice(key));
-    let mut block = GenericArray::clone_from_slice(data);
+    let cipher = Aes128::new(&(*key).into());
+    let mut block: Array<u8, _> = (*data).into();
    cipher.decrypt_block(&mut block);
    let mut out = [0u8; 16];
    out.copy_from_slice(&block);
@@ -79,6 +79,38 @@ impl Unlocker for AacsCert {
 mod tests {
    use super::*;

+    /// AES-128-ECB decrypt against the FIPS-197 Appendix B / NIST known-answer
+    /// test vector: decrypting the published ciphertext with the published key
+    /// must recover the published plaintext.
+    #[test]
+    fn aes_ecb_decrypt_matches_fips197_test_vector() {
+        let key: [u8; 16] = [
+            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D,
+            0x0E, 0x0F,
+        ];
+        let ciphertext: [u8; 16] = [
+            0x69, 0xC4, 0xE0, 0xD8, 0x6A, 0x7B, 0x04, 0x30, 0xD8, 0xCD, 0xB7, 0x80, 0x70, 0xB4,
+            0xC5, 0x5A,
+        ];
+        let expected_plaintext: [u8; 16] = [
+            0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD,
+            0xEE, 0xFF,
+        ];
+        let out = aes_ecb_decrypt(&key, &ciphertext);
+        assert_eq!(out, expected_plaintext);
+    }
+
+    /// Decrypting a different ciphertext under the same key must not produce
+    /// the same plaintext — pins that the function actually decrypts the
+    /// given block rather than returning a constant.
+    #[test]
+    fn aes_ecb_decrypt_varies_with_input() {
+        let key = [0u8; 16];
+        let a = aes_ecb_decrypt(&key, &[0u8; 16]);
+        let b = aes_ecb_decrypt(&key, &[1u8; 16]);
+        assert_ne!(a, b);
+    }
+
    fn id() -> crate::DriveId {
        crate::DriveId::default()
    }
@@ -108,6 +140,42 @@ mod tests {
        }
    }

+    /// `Default` must delegate to `new()` (there is only one way to build an
+    /// `AacsCert`, so this pins the two constructors never drift apart).
+    #[test]
+    #[allow(clippy::default_constructed_unit_structs)]
+    fn default_matches_new() {
+        let _ = AacsCert::default();
+        let _ = AacsCert::new();
+    }
+
+    /// THE full success path through `Unlocker::unlock_bus` itself: a
+    /// self-consistent AACS 1.0 drive emulator carries auth + VID + data-key
+    /// reads all the way to `Ok(Unlocked { .. })`, so the crate's public entry
+    /// point — not just `run_cert_handshake` underneath it — is proven to wire
+    /// `volume_id` and `read_data_key` into `Unlocked` correctly.
+    #[test]
+    fn unlock_bus_succeeds_end_to_end() {
+        let mut t = handshake::tests::DriveEmu::new();
+        t.serve_data_keys = true;
+        let id = id();
+        let certs = [host_cert()];
+        let ctx = UnlockCtx::new(&id, DiscKind::Aacs, &certs);
+        let unlocked = AacsCert::new()
+            .unlock_bus(&mut t, &ctx)
+            .expect("auth + VID + data-key reads all succeed");
+        assert_eq!(unlocked.vid, Some([0x5Au8; 16]));
+        assert!(unlocked.bus_key.is_some());
+        assert!(
+            !unlocked.drive_unlocked,
+            "cert path never sets drive_unlocked"
+        );
+    }
+
+    fn host_cert() -> crate::HostCert {
+        handshake::tests::dummy_cert()
+    }
+
    /// With no host certs there is nothing to authenticate with → NoUsableHostCert,
    /// and the transport is never touched.
    #[test]
@@ -19,6 +19,31 @@ impl Error {
            Error::Scsi(_) => 7299,
        }
    }
+
+    /// True if this is a transport-layer SCSI failure (bus dead).
+    pub fn is_transport_failure(&self) -> bool {
+        matches!(
+            self,
+            Error::Scsi(s)
+                if s.status == crate::scsi::SCSI_STATUS_TRANSPORT_FAILURE && s.sense.is_none()
+        )
+    }
+}
+
+/// Collapse a SCSI-layer failure from a bus-auth step onto the CSS auth code —
+/// but NEVER a transport fault.
+///
+/// Every step used to do `.map_err(|_| Error::CssAuthFailed)?`, which discarded
+/// the `ScsiError` whole. That made the `Transport` arm of the conversion below
+/// UNREACHABLE from any real call site: a dead bus arrived at the consumer as
+/// `NotApplicable`, so it fell through and kept probing a bus that was gone.
+pub fn step_err(e: crate::scsi::ScsiError) -> Error {
+    let err = Error::Scsi(e);
+    if err.is_transport_failure() {
+        err
+    } else {
+        Error::CssAuthFailed
+    }
 }

 impl From<crate::scsi::ScsiError> for Error {
@@ -31,11 +56,94 @@ impl From<crate::scsi::ScsiError> for Error {
 /// "this unlocker didn't apply" (a transport fault still surfaces as Transport).
 impl From<Error> for crate::UnlockError {
    fn from(e: Error) -> Self {
+        if e.is_transport_failure() {
+            crate::UnlockError::Transport
+        } else {
+            crate::UnlockError::NotApplicable
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::UnlockError;
+    use crate::scsi::{SCSI_STATUS_CHECK_CONDITION, SCSI_STATUS_TRANSPORT_FAILURE, ScsiError};
+
+    /// Catches restoring the `.map_err(|_| CssAuthFailed)` that made the
+    /// `Transport` arm unreachable: a dead bus must classify as `Transport`
+    /// (consumer aborts), a drive rejection as `NotApplicable` (fall through).
+    #[test]
+    fn transport_fault_survives_the_step_mapping() {
+        let dead = step_err(ScsiError {
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: None,
+        });
+        assert!(dead.is_transport_failure());
+        assert_eq!(UnlockError::from(dead), UnlockError::Transport);
+
+        let refused = step_err(ScsiError {
+            status: SCSI_STATUS_CHECK_CONDITION,
+            sense: Some([0u8; 32]),
+        });
+        assert!(matches!(refused, Error::CssAuthFailed));
+        assert_eq!(UnlockError::from(refused), UnlockError::NotApplicable);
+    }
+
+    /// Each variant has its own stable numeric code.
+    #[test]
+    fn code_is_stable_per_variant() {
+        assert_eq!(Error::CssAuthFailed.code(), 7201);
+        assert_eq!(
+            Error::Scsi(ScsiError {
+                status: SCSI_STATUS_CHECK_CONDITION,
+                sense: Some([0u8; 32]),
+            })
+            .code(),
+            7299
+        );
+    }
+
+    /// `is_transport_failure` is false for `CssAuthFailed`, false for a
+    /// `Scsi` error carrying a sense (a drive rejection, not a dead bus) even
+    /// at the transport-failure status, and true only for the genuine
+    /// transport fault (status + no sense).
+    #[test]
+    fn is_transport_failure_false_paths() {
+        assert!(!Error::CssAuthFailed.is_transport_failure());
+
+        let sensed = Error::Scsi(ScsiError {
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: Some([0u8; 32]),
+        });
+        assert!(!sensed.is_transport_failure());
+
+        let refusal = Error::Scsi(ScsiError {
+            status: SCSI_STATUS_CHECK_CONDITION,
+            sense: None,
+        });
+        assert!(!refusal.is_transport_failure());
+
+        let dead = Error::Scsi(ScsiError {
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: None,
+        });
+        assert!(dead.is_transport_failure());
+    }
+
+    /// `From<ScsiError>` wraps the transport error unchanged into `Error::Scsi`.
+    #[test]
+    fn from_scsi_error_wraps_into_scsi_variant() {
+        let e = Error::from(ScsiError {
+            status: SCSI_STATUS_CHECK_CONDITION,
+            sense: Some([1u8; 32]),
+        });
        match e {
-            Error::Scsi(s) if s.status == crate::scsi::SCSI_STATUS_TRANSPORT_FAILURE => {
-                crate::UnlockError::Transport
+            Error::Scsi(inner) => {
+                assert_eq!(inner.status, SCSI_STATUS_CHECK_CONDITION);
+                assert_eq!(inner.sense, Some([1u8; 32]));
            }
-            _ => crate::UnlockError::NotApplicable,
+            _ => panic!("expected Error::Scsi"),
        }
    }
 }
@@ -4,13 +4,56 @@
 //! CSS bus-auth handshake has set its Authentication Success Flag (ASF=1).
 //! [`unlock_css_reads`] runs that bus-auth challenge-response (which is what
 //! actually opens scrambled-sector reads), then a best-effort, non-fatal
-//! disc-key REPORT KEY. The bytes are NOT used as keys: the descramble title
-//! key is recovered keylessly by the Stevenson known-plaintext attack (see
-//! [`super::crack_key`]).
+//! disc-key REPORT KEY. The bytes are NOT used as keys: descrambling here is
+//! keyless — the descramble title key is recovered directly from the stream,
+//! so no device or player key is derived or needed.

 mod error;
-use crate::css::error::{Error, Result};
-use crate::scsi::ScsiTransport;
+use crate::css::error::{Error, Result, step_err};
+use crate::scsi::{DataDirection, ScsiTransport};
+
+/// Issue ONE CSS bus-auth CDB, honouring the transport contract.
+///
+/// The single seam every bus-auth step now goes through. It closes two holes
+/// that each step open-coded before:
+///   * `Err` was collapsed to `CssAuthFailed`, so a dead bus looked like "this
+///     unlocker doesn't apply" and the consumer kept probing it ([`step_err`]);
+///   * `Ok` was never inspected, but per the contract a CHECK CONDITION arrives
+///     as `Ok` with a non-zero `status` — so a refused command handed the step
+///     back its own zero-filled buffer to parse as drive data.
+///
+/// `min_bytes` is the number of bytes the step must actually receive (0 for a
+/// write / no-data command, whose transferred count no transport promises).
+fn css_scsi(
+    scsi: &mut dyn ScsiTransport,
+    cdb: &[u8],
+    dir: DataDirection,
+    buf: &mut [u8],
+    min_bytes: usize,
+) -> Result<()> {
+    let r = scsi.execute(cdb, dir, buf, 5_000).map_err(step_err)?;
+    if r.status != 0 {
+        tracing::debug!(
+            target: "freemkv::css",
+            phase = "css_step_check_condition",
+            opcode = cdb.first().copied().unwrap_or(0),
+            status = r.status,
+            "CSS bus-auth step returned a drive sense"
+        );
+        return Err(Error::CssAuthFailed);
+    }
+    if r.bytes_transferred < min_bytes {
+        tracing::debug!(
+            target: "freemkv::css",
+            phase = "css_step_short_response",
+            opcode = cdb.first().copied().unwrap_or(0),
+            bytes_transferred = r.bytes_transferred,
+            "CSS bus-auth step returned a short response"
+        );
+        return Err(Error::CssAuthFailed);
+    }
+    Ok(())
+}

 // ── CryptKey tables ───────────────────────────────────────────────────────

@@ -123,9 +166,10 @@ const PERM_VARIANT: [[u8; 32]; 2] = [
 /// Runs the bus-auth challenge-response (which sets the drive's ASF=1 and is
 /// what actually unlocks scrambled-sector reads), then a best-effort,
 /// non-fatal disc-key REPORT KEY. The title-key REPORT KEY is NOT issued: it
-/// is unnecessary (the descramble key is recovered keylessly by the Stevenson
-/// attack in [`super::crack_key`]) and its hard failure on some USB bridges
-/// used to abort the whole unlock (the 7014 bug). The bytes are discarded.
+/// is unnecessary (descrambling is keyless — the key is recovered directly
+/// from the data, so no device key is derived) and its hard failure on some
+/// USB bridges used to abort the whole unlock (the 7014 bug). The bytes are
+/// discarded.
 pub fn unlock_css_reads(scsi: &mut dyn ScsiTransport, lba: u32) -> Result<()> {
    let t0 = std::time::Instant::now();
    tracing::info!(target: "freemkv::css", phase = "unlock_css_reads", lba, "begin");
@@ -144,8 +188,8 @@ pub fn unlock_css_reads(scsi: &mut dyn ScsiTransport, lba: u32) -> Result<()> {
 /// The DVD unlocker (registry name `"DVD"`) — the DVD peer of the firmware and
 /// AACS-cert unlockers in the uniform [`crate::Unlocker`] registry. It removes
 /// the DVD scrambled-read barrier (drive ASF=1) via bus-auth and learns no VID
-/// or bus key — the descramble key is recovered keylessly downstream (the
-/// Stevenson attack). Named for the medium it unlocks (DVD), not the CSS
+/// or bus key — descrambling is keyless: the key is recovered directly from
+/// the data downstream. Named for the medium it unlocks (DVD), not the CSS
 /// scheme: the bus-auth is required to read a CSS-protected DVD at all, whether
 /// or not any given sector turns out to be scrambled. Lives in the `css` module
 /// beside the CSS-scheme primitives it drives.
@@ -187,7 +231,7 @@ impl crate::Unlocker for DvdUnlocker {
        // DiscKind alone. If the drive does not report a DVD profile, refuse
        // (NotApplicable) WITHOUT issuing any CSS CDB, so a mis-routed
        // Blu-ray/UHD is never sent CSS bus-auth.
-        if !mounted_disc_is_dvd(scsi) {
+        if !mounted_disc_is_dvd(scsi)? {
            tracing::debug!(
                target: "freemkv::css",
                phase = "dvd_unlocker_not_dvd",
@@ -206,7 +250,14 @@ impl crate::Unlocker for DvdUnlocker {
 /// Transport-level "is the mounted disc a DVD?" probe (GET CONFIGURATION
 /// current-profile, DVD family `0x0010..=0x001F`). Lets the DvdUnlocker
 /// self-verify against the drive instead of trusting the caller's DiscKind.
-fn mounted_disc_is_dvd(scsi: &mut dyn ScsiTransport) -> bool {
+///
+/// `Err(Transport)` on a dead bus. This is the FIRST command the DVD unlocker
+/// issues, and its match had no `Err` arm at all: a transport fault fell into
+/// `_ => false`, which the caller turned into `NotApplicable` — a dead bus read
+/// as "not a DVD", with nothing logged anywhere on the path.
+fn mounted_disc_is_dvd(
+    scsi: &mut dyn ScsiTransport,
+) -> std::result::Result<bool, crate::UnlockError> {
    // RT=0: the 8-byte feature header carries the Current Profile in bytes 6-7.
    let cdb = [
        crate::scsi::SCSI_GET_CONFIGURATION,
@@ -221,17 +272,34 @@ fn mounted_disc_is_dvd(scsi: &mut dyn ScsiTransport) -> bool {
        0x00,
    ];
    let mut buf = [0u8; 8];
-    match scsi.execute(
-        &cdb,
-        crate::scsi::DataDirection::FromDevice,
-        &mut buf,
-        5_000,
-    ) {
-        Ok(r) if r.bytes_transferred >= 8 => {
+    match scsi.execute(&cdb, DataDirection::FromDevice, &mut buf, 5_000) {
+        Ok(r) if r.status == 0 && r.bytes_transferred >= 8 => {
            let profile = ((buf[6] as u16) << 8) | buf[7] as u16;
-            (0x0010..=0x001F).contains(&profile)
+            Ok((0x0010..=0x001F).contains(&profile))
+        }
+        // A drive sense or a short reply genuinely means "can't tell / not a
+        // DVD" — decline, but say so.
+        Ok(r) => {
+            tracing::debug!(
+                target: "freemkv::css",
+                phase = "dvd_profile_probe_inconclusive",
+                status = r.status,
+                bytes_transferred = r.bytes_transferred,
+                "GET CONFIGURATION did not report a current profile"
+            );
+            Ok(false)
+        }
+        Err(e) => {
+            let err = crate::css::error::step_err(e);
+            tracing::warn!(
+                target: "freemkv::css",
+                phase = "dvd_profile_probe_failed",
+                error_code = err.code(),
+                transport_failure = err.is_transport_failure(),
+                "GET CONFIGURATION failed while probing for a DVD"
+            );
+            Err(crate::UnlockError::from(err))
        }
-        _ => false,
    }
 }

@@ -265,42 +333,56 @@ fn unlock_css_reads_inner(scsi: &mut dyn ScsiTransport, _lba: u32) -> Result<()>
 /// Success Flag (ASF=1) — which is the ENTIRE purpose: it unlocks
 /// scrambled-sector reads. Returns the negotiated AGID (the caller needs it for
 /// the best-effort disc-key REPORT KEY). The CSS bus key is intentionally NOT
-/// derived: descrambling is keyless (the Stevenson known-plaintext attack), so
-/// the bus key has no consumer.
+/// derived: descrambling is keyless — the key is recovered directly from the
+/// data — so the bus key has no consumer.
 fn establish_authenticated_session(scsi: &mut dyn ScsiTransport) -> Result<u8> {
-    // Invalidate all AGIDs via REPORT KEY format 0x3F
+    // Invalidate all AGIDs via REPORT KEY format 0x3F. This is also what makes
+    // an abandoned AGID self-heal — which is not a reason to abandon one.
    for agid in 0..4u8 {
-        let mut cdb = [0u8; 12];
-        cdb[0] = crate::scsi::SCSI_REPORT_KEY;
-        // alloc_len = 0 (no data transfer)
-        cdb[10] = (agid << 6) | 0x3F;
-        let mut buf = [0u8; 8];
-        let _ = scsi.execute(
-            &cdb,
-            crate::scsi::DataDirection::FromDevice,
-            &mut buf,
-            5_000,
-        );
+        release_agid(scsi, agid);
    }

    // Allocate AGID
    let mut buf = [0u8; 8];
-    scsi.execute(
+    css_scsi(
+        scsi,
        &report_key_cdb(0, 0x00, 8),
-        crate::scsi::DataDirection::FromDevice,
+        DataDirection::FromDevice,
        &mut buf,
-        5_000,
-    )
-    .map_err(|_| Error::CssAuthFailed)?;
+        8,
+    )?;
    let agid = (buf[7] >> 6) & 0x03;

+    // From here on we hold the AGID; release it on any failure (see
+    // [`release_agid`]) instead of abandoning it.
+    let r = authenticate_with_agid(scsi, agid);
+    if r.is_err() {
+        release_agid(scsi, agid);
+    }
+    r.map(|()| agid)
+}
+
+/// Release an AGID (REPORT KEY format 0x3F). Best-effort: a failure to release
+/// is not a failure of the operation that is already failing.
+fn release_agid(scsi: &mut dyn ScsiTransport, agid: u8) {
+    let mut cdb = [0u8; 12];
+    cdb[0] = crate::scsi::SCSI_REPORT_KEY;
+    cdb[10] = (agid << 6) | 0x3F;
+    let mut buf = [0u8; 8];
+    let _ = scsi.execute(&cdb, DataDirection::FromDevice, &mut buf, 5_000);
+}
+
+/// The challenge-response half of [`establish_authenticated_session`], with the
+/// AGID already allocated. Split out so its caller can release the AGID on any
+/// failure without a Drop guard or a release at each early return.
+fn authenticate_with_agid(scsi: &mut dyn ScsiTransport, agid: u8) -> Result<()> {
    // Host sends challenge. The spec wants a fresh per-session random nonce,
    // not a fixed constant — a predictable challenge weakens the bus-auth
    // handshake.
    let mut host_challenge = [0u8; 10];
    {
-        use rand::RngCore;
-        rand::thread_rng().fill_bytes(&mut host_challenge);
+        use rand::Rng;
+        rand::rng().fill_bytes(&mut host_challenge);
    }
    let mut hc_buf = [0u8; 16];
    hc_buf[0] = 0x00;
@@ -308,23 +390,23 @@ fn establish_authenticated_session(scsi: &mut dyn ScsiTransport) -> Result<u8> {
    for i in 0..10 {
        hc_buf[4 + i] = host_challenge[9 - i];
    }
-    scsi.execute(
+    css_scsi(
+        scsi,
        &send_key_cdb(agid, 0x01, 16),
-        crate::scsi::DataDirection::ToDevice,
+        DataDirection::ToDevice,
        &mut hc_buf,
-        5_000,
-    )
-    .map_err(|_| Error::CssAuthFailed)?;
+        0,
+    )?;

    // Get Key1 from drive
    let mut dk_buf = [0u8; 12];
-    scsi.execute(
+    css_scsi(
+        scsi,
        &report_key_cdb(agid, 0x02, 12),
-        crate::scsi::DataDirection::FromDevice,
+        DataDirection::FromDevice,
        &mut dk_buf,
-        5_000,
-    )
-    .map_err(|_| Error::CssAuthFailed)?;
+        12,
+    )?;
    let mut key1 = [0u8; 5];
    for i in 0..5 {
        key1[i] = dk_buf[4 + (4 - i)];
@@ -342,13 +424,13 @@ fn establish_authenticated_session(scsi: &mut dyn ScsiTransport) -> Result<u8> {

    // Get drive challenge
    let mut dc_buf = [0u8; 16];
-    scsi.execute(
+    css_scsi(
+        scsi,
        &report_key_cdb(agid, 0x01, 16),
-        crate::scsi::DataDirection::FromDevice,
+        DataDirection::FromDevice,
        &mut dc_buf,
-        5_000,
-    )
-    .map_err(|_| Error::CssAuthFailed)?;
+        16,
+    )?;
    let mut drive_challenge = [0u8; 10];
    for i in 0..10 {
        drive_challenge[i] = dc_buf[4 + (9 - i)];
@@ -362,25 +444,27 @@ fn establish_authenticated_session(scsi: &mut dyn ScsiTransport) -> Result<u8> {
    for i in 0..5 {
        hk_buf[4 + i] = key2[4 - i];
    }
-    scsi.execute(
+    css_scsi(
+        scsi,
        &send_key_cdb(agid, 0x03, 12),
-        crate::scsi::DataDirection::ToDevice,
+        DataDirection::ToDevice,
        &mut hk_buf,
-        5_000,
-    )
-    .map_err(|_| Error::CssAuthFailed)?;
+        0,
+    )?;

    // The authenticated session (ASF=1) is now established — scrambled-sector
    // reads are unlocked, which is the only thing we needed. The CSS bus key
    // would be CryptKey(2, variant, key1 || key2), but it has no consumer
-    // (descrambling is keyless via the Stevenson attack), so it is not derived.
-    Ok(agid)
+    // (descrambling is keyless — the key is recovered directly from the
+    // data), so it is not derived.
+    Ok(())
 }

 // ── Step 2: Disc Key ──────────────────────────────────────────────────────

-/// Issue READ DVD STRUCTURE format 0x02 (Copyright Information — opcode 0xAD,
-/// NOT the REPORT KEY 0xA4 disc-key block) purely for the bus-auth unlock side
+/// Issue READ DVD STRUCTURE format 0x02 (the Disc Key block — opcode 0xAD, NOT
+/// the REPORT KEY 0xA4 disc-key block; format 0x01 is Copyright Information)
+/// purely for the bus-auth unlock side
 /// effect. The returned block contents are not used — the descramble title key
 /// is recovered keylessly elsewhere, so the genuine disc-key REPORT KEY is
 /// intentionally skipped. (If a drive is ever found where bus-auth alone does
@@ -397,14 +481,10 @@ fn read_disc_key(scsi: &mut dyn ScsiTransport, agid: u8) -> Result<()> {
    cdb[9] = alloc_len as u8;
    cdb[10] = agid << 6;

+    // Best-effort by design (the caller logs and continues), but a transport
+    // fault still has to be distinguishable from a drive that declined.
    let mut buf = vec![0u8; alloc_len as usize];
-    let dvd_result = scsi.execute(
-        &cdb,
-        crate::scsi::DataDirection::FromDevice,
-        &mut buf,
-        5_000,
-    );
-    dvd_result.map_err(|_| Error::CssAuthFailed)?;
+    css_scsi(scsi, &cdb, DataDirection::FromDevice, &mut buf, 0)?;

    Ok(())
 }
@@ -943,6 +1023,15 @@ mod tests {
        assert_eq!(DvdUnlocker::new().name(), "DVD");
    }

+    /// `Default` must delegate to `new()` — there is only one way to build a
+    /// `DvdUnlocker` (it is a unit struct), so this pins the two never drift.
+    #[test]
+    #[allow(clippy::default_constructed_unit_structs)]
+    fn default_matches_new() {
+        let _ = DvdUnlocker::default();
+        let _ = DvdUnlocker::new();
+    }
+
    /// DvdUnlocker provides bus removal only — it never provides drive features.
    #[test]
    fn dvd_unlocker_provides_no_features() {
@@ -1026,4 +1115,437 @@ mod tests {
            "no CSS CDB may be issued at a non-DVD drive"
        );
    }
+    // ── Transport-contract tests ────────────────────────────────────────────
+
+    use crate::scsi::mock::{MockTransport, Reply};
+    use crate::{DiscKind, DriveId, UnlockCtx, UnlockError, Unlocker};
+
+    /// THE defect-7 test. `mounted_disc_is_dvd` is the FIRST command the DVD
+    /// unlocker issues and its match had no `Err` arm: a transport fault fell
+    /// into `_ => false`, so a dead bus was reported as "not a DVD"
+    /// (`NotApplicable`) and the consumer kept probing it — with nothing logged
+    /// anywhere on the path. Catches restoring that catch-all arm.
+    #[test]
+    fn transport_fault_probing_for_a_dvd_aborts() {
+        let id = DriveId::default();
+        let mut t = MockTransport::always(Reply::TransportFault);
+        let r = DvdUnlocker::new().unlock_bus(&mut t, &UnlockCtx::new(&id, DiscKind::Css, &[]));
+        assert_eq!(r.unwrap_err(), UnlockError::Transport);
+        assert_eq!(
+            t.calls(),
+            1,
+            "must abort on the first command, not probe on"
+        );
+    }
+
+    /// A drive that REFUSES GET CONFIGURATION (CHECK CONDITION, delivered as
+    /// `Ok` per the contract) is inconclusive, not a dead bus → decline. Guards
+    /// against over-correcting defect 7 into "any probe failure aborts the rip".
+    #[test]
+    fn check_condition_probing_for_a_dvd_declines() {
+        let id = DriveId::default();
+        let mut t = MockTransport::always(Reply::illegal_request());
+        let r = DvdUnlocker::new().unlock_bus(&mut t, &UnlockCtx::new(&id, DiscKind::Css, &[]));
+        assert_eq!(r.unwrap_err(), UnlockError::NotApplicable);
+    }
+
+    /// A DVD is mounted, then the bus dies during bus-auth. THE defect-2 test:
+    /// every CSS step used to do `.map_err(|_| CssAuthFailed)`, discarding the
+    /// `ScsiError` and making the `Transport` arm of the error conversion
+    /// unreachable from any real call site — so a dead bus arrived as
+    /// `NotApplicable` and the consumer went on probing it.
+    #[test]
+    fn transport_fault_during_bus_auth_aborts() {
+        let id = DriveId::default();
+        // GET CONFIGURATION reports a DVD-ROM profile (0x0010), then the bus dies.
+        let mut config = vec![0u8; 8];
+        config[6] = 0x00;
+        config[7] = 0x10;
+        let mut t = MockTransport::scripted(vec![Reply::good(config)], Reply::TransportFault);
+        let r = DvdUnlocker::new().unlock_bus(&mut t, &UnlockCtx::new(&id, DiscKind::Css, &[]));
+        assert_eq!(r.unwrap_err(), UnlockError::Transport);
+    }
+
+    /// The same shape with the drive REFUSING the bus-auth commands: a CSS
+    /// auth failure is a fall-through, not an abort.
+    #[test]
+    fn drive_refusing_bus_auth_is_not_applicable() {
+        let id = DriveId::default();
+        let mut config = vec![0u8; 8];
+        config[7] = 0x10;
+        let mut t = MockTransport::scripted(vec![Reply::good(config)], Reply::illegal_request());
+        let r = DvdUnlocker::new().unlock_bus(&mut t, &UnlockCtx::new(&id, DiscKind::Css, &[]));
+        assert_eq!(r.unwrap_err(), UnlockError::NotApplicable);
+    }
+
+    /// A conforming transport answering the AGID allocation with a CHECK
+    /// CONDITION must NOT let the handshake carry on off the caller's own
+    /// zero-filled buffer (agid 0, a challenge answered by zeros). Catches
+    /// dropping the `status` check in `css_scsi`.
+    #[test]
+    fn agid_allocation_check_condition_fails_the_auth() {
+        // 4 AGID invalidations are best-effort; the 5th command is the alloc.
+        let mut t = MockTransport::scripted(
+            vec![
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+            ],
+            Reply::illegal_request(),
+        );
+        let e = establish_authenticated_session(&mut t).expect_err("refused alloc");
+        assert!(matches!(e, Error::CssAuthFailed));
+    }
+
+    /// Defect 18: an AGID allocated and then lost to a failed challenge must be
+    /// RELEASED (REPORT KEY format 0x3F), not abandoned. A drive has four; the
+    /// leak self-heals because the next session invalidates all of them, but
+    /// leaving a drive short between attempts is a state we should not create.
+    #[test]
+    fn a_failed_handshake_releases_the_agid_it_allocated() {
+        let mut t = MockTransport::scripted(
+            vec![
+                Reply::good(vec![0u8; 8]), // 4 × AGID invalidate
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]), // AGID allocated
+            ],
+            Reply::illegal_request(), // every challenge step is refused
+        );
+        establish_authenticated_session(&mut t).expect_err("refused challenge");
+        let last = t.cdbs.last().expect("commands were issued");
+        assert_eq!(last[0], crate::scsi::SCSI_REPORT_KEY);
+        assert_eq!(last[10] & 0x3F, 0x3F, "AGID released on the failure path");
+    }
+
+    /// A short AGID-allocation response is equally unusable — the AGID would be
+    /// read out of bytes the drive never sent.
+    #[test]
+    fn short_agid_allocation_fails_the_auth() {
+        let mut t = MockTransport::scripted(
+            vec![
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+                Reply::good(vec![0u8; 8]),
+            ],
+            Reply::short(vec![0u8; 8], 3),
+        );
+        let e = establish_authenticated_session(&mut t).expect_err("short alloc");
+        assert!(matches!(e, Error::CssAuthFailed));
+    }
+
+    // ── authenticate_with_agid step failures ────────────────────────────────
+
+    /// The drive refuses the host-challenge SEND KEY (step 1) — the very first
+    /// command `authenticate_with_agid` issues.
+    #[test]
+    fn host_challenge_send_failure_fails_the_auth() {
+        let mut t =
+            MockTransport::scripted(vec![Reply::illegal_request()], Reply::illegal_request());
+        let e = authenticate_with_agid(&mut t, 0).expect_err("refused host challenge");
+        assert!(matches!(e, Error::CssAuthFailed));
+        assert_eq!(t.calls(), 1, "must not proceed past the first refused step");
+    }
+
+    /// The host challenge SEND KEY succeeds but the Key1 REPORT KEY (step 2) is
+    /// refused.
+    #[test]
+    fn key1_report_failure_fails_the_auth() {
+        let mut t = MockTransport::scripted(
+            vec![Reply::good(vec![]), Reply::illegal_request()],
+            Reply::illegal_request(),
+        );
+        let e = authenticate_with_agid(&mut t, 0).expect_err("refused Key1 report");
+        assert!(matches!(e, Error::CssAuthFailed));
+        assert_eq!(t.calls(), 2);
+    }
+
+    /// Both SCSI steps succeed but the drive's Key1 does not match any of the
+    /// 32 CryptKey variants for the (randomly generated) host challenge — the
+    /// brute-force loop exhausts and `variant.ok_or(CssAuthFailed)` fires.
+    #[test]
+    fn key1_matching_no_variant_fails_the_auth() {
+        let mut t = MockTransport::scripted(
+            vec![Reply::good(vec![]), Reply::good(vec![0xABu8; 12])],
+            Reply::illegal_request(),
+        );
+        let e = authenticate_with_agid(&mut t, 0).expect_err("no variant matches");
+        assert!(matches!(e, Error::CssAuthFailed));
+        assert_eq!(
+            t.calls(),
+            2,
+            "the brute-force loop issues no further SCSI commands"
+        );
+    }
+
+    /// Host challenge + Key1 both succeed, but the drive challenge REPORT KEY
+    /// (step 3) is refused. Distinct from `key1_report_failure_fails_the_auth`
+    /// (step 2) and `key2_send_failure_fails_the_auth` (step 4) below — each
+    /// pins a different `css_scsi` call site's `?`.
+    #[test]
+    fn drive_challenge_report_failure_fails_the_auth() {
+        struct FailAtDriveChallenge(FakeDvdDrive);
+        impl ScsiTransport for FailAtDriveChallenge {
+            fn execute(
+                &mut self,
+                cdb: &[u8],
+                dir: DataDirection,
+                data: &mut [u8],
+                timeout_ms: u32,
+            ) -> crate::scsi::Result<crate::scsi::ScsiResult> {
+                if cdb[0] == crate::scsi::SCSI_REPORT_KEY && cdb[10] & 0x3F == 0x01 {
+                    return Ok(crate::scsi::ScsiResult {
+                        status: 0x02,
+                        bytes_transferred: 0,
+                        sense: [0u8; 32],
+                    });
+                }
+                self.0.execute(cdb, dir, data, timeout_ms)
+            }
+        }
+        let mut t = FailAtDriveChallenge(FakeDvdDrive {
+            variant: 4,
+            host_challenge: [0u8; 10],
+        });
+        let e = authenticate_with_agid(&mut t, 0).expect_err("refused drive challenge");
+        assert!(matches!(e, Error::CssAuthFailed));
+    }
+
+    /// Host challenge, Key1, and the drive challenge all succeed, but the
+    /// Key2 SEND KEY (step 4, the last command in the handshake) is refused.
+    #[test]
+    fn key2_send_failure_fails_the_auth() {
+        struct FailAtKey2Send(FakeDvdDrive);
+        impl ScsiTransport for FailAtKey2Send {
+            fn execute(
+                &mut self,
+                cdb: &[u8],
+                dir: DataDirection,
+                data: &mut [u8],
+                timeout_ms: u32,
+            ) -> crate::scsi::Result<crate::scsi::ScsiResult> {
+                if cdb[0] == crate::scsi::SCSI_SEND_KEY && cdb[10] & 0x3F == 0x03 {
+                    return Ok(crate::scsi::ScsiResult {
+                        status: 0x02,
+                        bytes_transferred: 0,
+                        sense: [0u8; 32],
+                    });
+                }
+                self.0.execute(cdb, dir, data, timeout_ms)
+            }
+        }
+        let mut t = FailAtKey2Send(FakeDvdDrive {
+            variant: 4,
+            host_challenge: [0u8; 10],
+        });
+        let e = authenticate_with_agid(&mut t, 0).expect_err("refused Key2 send");
+        assert!(matches!(e, Error::CssAuthFailed));
+    }
+
+    // ── read_disc_key ────────────────────────────────────────────────────────
+
+    /// The best-effort disc-key REPORT KEY is refused — `read_disc_key` must
+    /// surface the failure to its caller (who treats it as non-fatal), not
+    /// silently return `Ok`.
+    #[test]
+    fn read_disc_key_refused_is_an_error() {
+        let mut t = MockTransport::always(Reply::illegal_request());
+        let e = read_disc_key(&mut t, 0).expect_err("drive refused disc-key read");
+        assert!(matches!(e, Error::CssAuthFailed));
+    }
+
+    /// A transport fault reading the disc key must classify as a transport
+    /// failure, not a generic auth failure.
+    #[test]
+    fn read_disc_key_transport_fault_is_transport_failure() {
+        let mut t = MockTransport::always(Reply::TransportFault);
+        let e = read_disc_key(&mut t, 0).expect_err("dead bus");
+        assert!(e.is_transport_failure());
+    }
+
+    // ── Full happy-path bus-auth ────────────────────────────────────────────
+
+    /// A fake drive that plays its half of the CSS bus-auth handshake for
+    /// real: it captures the host's genuinely-random per-session challenge
+    /// and answers Key1 with the actual `crypt_key(0, variant, ..)` for a
+    /// fixed `variant`, so the host's brute-force loop matches it honestly
+    /// (not via a canned constant the loop happens to hit). Also answers
+    /// GET CONFIGURATION as a DVD and READ DVD STRUCTURE (disc key) as a
+    /// success, so the full `unlock_bus` path can be driven end to end.
+    struct FakeDvdDrive {
+        variant: u8,
+        host_challenge: [u8; 10],
+    }
+
+    impl ScsiTransport for FakeDvdDrive {
+        fn execute(
+            &mut self,
+            cdb: &[u8],
+            _dir: DataDirection,
+            data: &mut [u8],
+            _timeout_ms: u32,
+        ) -> crate::scsi::Result<crate::scsi::ScsiResult> {
+            use crate::scsi::ScsiResult;
+            let ok = |bytes_transferred: usize| ScsiResult {
+                status: 0,
+                bytes_transferred,
+                sense: [0u8; 32],
+            };
+            match cdb[0] {
+                crate::scsi::SCSI_GET_CONFIGURATION => {
+                    data[6] = 0x00;
+                    data[7] = 0x10; // DVD-ROM current profile
+                    Ok(ok(8))
+                }
+                crate::scsi::SCSI_SEND_KEY => {
+                    let format = cdb[10] & 0x3F;
+                    if format == 0x01 {
+                        // Host challenge: capture it for the Key1 answer.
+                        for i in 0..10 {
+                            self.host_challenge[i] = data[4 + (9 - i)];
+                        }
+                    }
+                    // format 0x03 (Key2) is accepted unconditionally: the
+                    // real handshake never verifies it drive-side in this
+                    // primitive (ASF=1 is set on the drive's own say-so).
+                    Ok(ok(0))
+                }
+                crate::scsi::SCSI_REPORT_KEY => {
+                    match cdb[10] & 0x3F {
+                        0x00 => {
+                            // Allocate AGID 0.
+                            data[7] = 0x00;
+                            Ok(ok(8))
+                        }
+                        0x02 => {
+                            // Key1, honestly derived from the captured challenge.
+                            let key1 = crypt_key(0, self.variant, &self.host_challenge);
+                            for i in 0..5 {
+                                data[4 + (4 - i)] = key1[i];
+                            }
+                            Ok(ok(12))
+                        }
+                        0x01 => {
+                            // Drive challenge (arbitrary, fixed).
+                            let drive_challenge: [u8; 10] = [9, 8, 7, 6, 5, 4, 3, 2, 1, 0];
+                            for i in 0..10 {
+                                data[4 + (9 - i)] = drive_challenge[i];
+                            }
+                            Ok(ok(16))
+                        }
+                        _ => Ok(ok(0)), // 0x3F release, best-effort
+                    }
+                }
+                crate::scsi::SCSI_READ_DISC_STRUCTURE => Ok(ok(2048 + 4)),
+                _ => Ok(ok(0)),
+            }
+        }
+    }
+
+    /// End-to-end happy path for the bus-auth handshake: AGID allocation,
+    /// host challenge, a Key1 that genuinely matches the brute-forced
+    /// variant, the drive-challenge/Key2 exchange, and the disc-key REPORT
+    /// KEY all succeed. Exercises `establish_authenticated_session`'s `Ok`
+    /// return and `read_disc_key`'s success path, neither of which the
+    /// failure-path tests above reach.
+    #[test]
+    fn full_bus_auth_and_disc_key_succeed() {
+        let mut t = FakeDvdDrive {
+            variant: 7,
+            host_challenge: [0u8; 10],
+        };
+        let agid =
+            establish_authenticated_session(&mut t).expect("full bus-auth handshake succeeds");
+        assert_eq!(agid, 0);
+        read_disc_key(&mut t, agid).expect("disc-key REPORT KEY succeeds");
+    }
+
+    /// The same happy path driven through the public `unlock_bus` entry
+    /// point (DVD self-guard, full bus-auth, best-effort disc key), proving
+    /// `DvdUnlocker::unlock_bus` returns `Ok(Unlocked::default())` on success
+    /// — the path every failure-injection test above deliberately avoids.
+    #[test]
+    fn dvd_unlocker_succeeds_end_to_end() {
+        let id = DriveId::default();
+        let mut t = FakeDvdDrive {
+            variant: 3,
+            host_challenge: [0u8; 10],
+        };
+        let r = DvdUnlocker::new().unlock_bus(&mut t, &UnlockCtx::new(&id, DiscKind::Css, &[]));
+        let unlocked = r.expect("full unlock succeeds");
+        assert!(unlocked.vid.is_none(), "CSS yields no Volume ID");
+        assert!(unlocked.bus_key.is_none(), "CSS yields no AACS bus key");
+        assert!(
+            !unlocked.drive_unlocked,
+            "CSS is a bus-auth unlock, not a firmware drive-unlock"
+        );
+    }
+
+    /// `unlock_css_reads` (the crate-level public entry point, distinct from
+    /// the `DvdUnlocker` wrapper) also succeeds end to end.
+    #[test]
+    fn unlock_css_reads_succeeds() {
+        let mut t = FakeDvdDrive {
+            variant: 11,
+            host_challenge: [0u8; 10],
+        };
+        // unlock_css_reads doesn't probe GET CONFIGURATION itself (that's
+        // DvdUnlocker's job); it goes straight to bus-auth.
+        unlock_css_reads(&mut t, 0).expect("css bus-auth + best-effort disc key succeed");
+    }
+
+    /// A drive whose bus-auth succeeds but refuses the best-effort disc-key
+    /// REPORT KEY (CHECK CONDITION). `unlock_css_reads_inner` must swallow
+    /// that failure — the read barrier is already open from bus-auth, so the
+    /// whole unlock must still report `Ok`, not propagate the disc-key error.
+    struct DiscKeyRefusingDrive(FakeDvdDrive);
+
+    impl ScsiTransport for DiscKeyRefusingDrive {
+        fn execute(
+            &mut self,
+            cdb: &[u8],
+            dir: DataDirection,
+            data: &mut [u8],
+            timeout_ms: u32,
+        ) -> crate::scsi::Result<crate::scsi::ScsiResult> {
+            if cdb[0] == crate::scsi::SCSI_READ_DISC_STRUCTURE {
+                return Ok(crate::scsi::ScsiResult {
+                    status: 0x02,
+                    bytes_transferred: 0,
+                    sense: [0u8; 32],
+                });
+            }
+            self.0.execute(cdb, dir, data, timeout_ms)
+        }
+    }
+
+    #[test]
+    fn disc_key_refusal_is_non_fatal_to_the_overall_unlock() {
+        let mut t = DiscKeyRefusingDrive(FakeDvdDrive {
+            variant: 5,
+            host_challenge: [0u8; 10],
+        });
+        unlock_css_reads(&mut t, 0)
+            .expect("bus-auth succeeded; a refused best-effort disc-key read must not fail it");
+    }
+
+    /// `crypt_key`'s `key_type == 2` arm (`PERM_VARIANT[1]`) has no
+    /// production caller (only key_type 0, the variant brute-force, and 1,
+    /// the drive-challenge Key2, are ever invoked from `authenticate_with_agid`)
+    /// but is a pure, directly-testable function of its documented contract.
+    #[test]
+    fn crypt_key_type2_is_deterministic_and_distinct_from_type1() {
+        let challenge: [u8; 10] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+        let a = crypt_key(2, 9, &challenge);
+        let b = crypt_key(2, 9, &challenge);
+        assert_eq!(a, b, "crypt_key(2, ..) must be deterministic");
+        assert_ne!(
+            crypt_key(1, 9, &challenge),
+            crypt_key(2, 9, &challenge),
+            "key_type 1 and 2 must diverge (distinct PERM_VARIANT rows)"
+        );
+    }
 }
@@ -1,6 +1,6 @@
-# ld — the LibreDrive unlocker
+# ld — the drive bus-unlock module

-The **LibreDrive** unlocker module for freemkv-unlock.
+A drive bus-unlock module for freemkv-unlock.

 freemkv-unlock defines the generic `Unlocker` contract; this module is one
 implementation of it. It recognizes a bundled catalog of supported drives
@@ -19,9 +19,3 @@ This module performs only the **non-persistent** unlock — the access state it
 sets up lives in drive RAM and is gone on power cycle. The one-time, permanent
 drive preparation is the drive owner's own manual step and is **never**
 automated here.
-
-## Credits
-
-LibreDrive was created by **Mike Chen** and the **MakeMKV team**. This module
-builds on their work — our thanks and full credit to them for the LibreDrive
-capabilities.
@@ -1,7 +1,7 @@
 //! Public unlock-CDB seam.
 //!
 //! These items expose the *minimum* an external consumer (e.g. the bdemu
-//! drive emulator) needs to recognise and answer the LibreDrive unlock
+//! drive emulator) needs to recognise and answer the Mt1959Unlocker unlock
 //! READ_BUFFER handshake, without that consumer open-coding the
 //! handshake internals. The concrete CDB shapes and the verification
 //! marker are unlock-handshake details and must live ONLY in this crate.
@@ -15,7 +15,7 @@ pub const UNLOCK_MARKER: &[u8] = b"MMkv";

 /// Returns `true` when a READ_BUFFER (`0x3C`) CDB with the given mode
 /// (`cdb[1] & 0x1F`) and buffer id (`cdb[2]`) is an unlock-handshake
-/// read — i.e. one of the LibreDrive unlock variants.
+/// read — i.e. one of the Mt1959Unlocker unlock variants.
 ///
 /// This is the single source of truth for the unlock READ_BUFFER CDB
 /// shapes; consumers must call it rather than hardcoding the mode /
@@ -39,6 +39,17 @@ impl std::fmt::Display for Error {
 impl std::error::Error for Error {}

 impl Error {
+    /// Stable numeric code (logged). Values are local to this crate and share
+    /// the crate-wide space with `aacs` (70xx) and `css` (72xx).
+    pub fn code(&self) -> u16 {
+        match self {
+            Error::ProfileParse => 7101,
+            Error::UnlockFailed => 7102,
+            Error::SignatureMismatch { .. } => 7103,
+            Error::Scsi { .. } => 7199,
+        }
+    }
+
    /// True if this is a transport-layer SCSI failure (bus dead), as opposed to a
    /// drive sense or a logical failure.
    pub(crate) fn is_transport_failure(&self) -> bool {
@@ -74,3 +85,120 @@ impl From<Error> for crate::UnlockError {
        }
    }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::UnlockError;
+    use crate::scsi::{SCSI_STATUS_CHECK_CONDITION, SCSI_STATUS_TRANSPORT_FAILURE, ScsiError};
+
+    /// The abort/fall-through boundary, which had no test at all. Catches
+    /// widening `is_transport_failure` (every failure would abort every rip) or
+    /// narrowing it (a dead bus would be probed forever).
+    #[test]
+    fn only_a_senseless_transport_status_is_a_transport_failure() {
+        let dead_bus = Error::Scsi {
+            opcode: 0x3C,
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: None,
+        };
+        assert!(dead_bus.is_transport_failure());
+        assert_eq!(UnlockError::from(dead_bus), UnlockError::Transport);
+
+        // A CHECK CONDITION is the DRIVE refusing, not the bus dying.
+        let refused = Error::Scsi {
+            opcode: 0x3C,
+            status: SCSI_STATUS_CHECK_CONDITION,
+            sense: Some([0u8; 32]),
+        };
+        assert!(!refused.is_transport_failure());
+        assert_eq!(UnlockError::from(refused), UnlockError::NotApplicable);
+
+        // The transport-failure status WITH a sense is a drive that reported
+        // 0xFF, not a bus fault — it must not abort the consumer.
+        let odd = Error::Scsi {
+            opcode: 0x3C,
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: Some([0u8; 32]),
+        };
+        assert!(!odd.is_transport_failure());
+
+        for e in [
+            Error::ProfileParse,
+            Error::UnlockFailed,
+            Error::SignatureMismatch {
+                expected: [0; 4],
+                got: [1; 4],
+            },
+        ] {
+            assert!(!e.is_transport_failure(), "{e:?} is not a bus fault");
+            assert_eq!(UnlockError::from(e), UnlockError::NotApplicable);
+        }
+    }
+
+    /// `Display` is what shows up in logs — every variant must render without
+    /// panicking and the SCSI variant must carry the opcode/status through.
+    #[test]
+    fn display_renders_every_variant() {
+        assert_eq!(Error::ProfileParse.to_string(), "drive profile parse error");
+        assert_eq!(Error::UnlockFailed.to_string(), "firmware unlock failed");
+        assert_eq!(
+            Error::SignatureMismatch {
+                expected: [0; 4],
+                got: [1; 4],
+            }
+            .to_string(),
+            "signature mismatch"
+        );
+        assert_eq!(
+            Error::Scsi {
+                opcode: 0x3C,
+                status: 0x02,
+                sense: None,
+            }
+            .to_string(),
+            "SCSI error (opcode 0x3c, status 0x02)"
+        );
+    }
+
+    /// `From<ScsiError>` must carry the status AND sense across the seam —
+    /// collapsing either one destroys the transport-vs-rejection distinction the
+    /// whole abort/fall-through split rests on.
+    #[test]
+    fn scsi_error_conversion_preserves_status_and_sense() {
+        let e = Error::from(ScsiError {
+            status: SCSI_STATUS_TRANSPORT_FAILURE,
+            sense: None,
+        });
+        assert!(e.is_transport_failure());
+
+        let e = Error::from(ScsiError {
+            status: SCSI_STATUS_CHECK_CONDITION,
+            sense: Some([0u8; 32]),
+        });
+        assert!(!e.is_transport_failure());
+        assert_eq!(UnlockError::from(e), UnlockError::NotApplicable);
+    }
+
+    /// Error codes are stable and distinct — they are the numeric contract the
+    /// logs carry instead of English.
+    #[test]
+    fn error_codes_are_distinct_and_stable() {
+        let codes = [
+            Error::ProfileParse.code(),
+            Error::UnlockFailed.code(),
+            Error::SignatureMismatch {
+                expected: [0; 4],
+                got: [0; 4],
+            }
+            .code(),
+            Error::Scsi {
+                opcode: 0,
+                status: 0,
+                sense: None,
+            }
+            .code(),
+        ];
+        assert_eq!(codes, [7101, 7102, 7103, 7199]);
+    }
+}
@@ -1,4 +1,4 @@
-//! ld — the LibreDrive firmware unlocker (MediaTek MT1959).
+//! ld — the MediaTek MT1959 firmware unlocker.
 //!
 //! Self-contained module: it owns the bundled drive profiles, firmware blobs,
 //! the WRITE_BUFFER / MODE SELECT upload, the unlock CDBs, and the variant-A /
@@ -10,7 +10,10 @@
 // needs (the real unlocker drives its CDBs from per-drive profile templates, not
 // these constants). Compile it only when the `emulation` feature exposes it, so
 // it never dead-codes in a normal build.
-#[cfg(feature = "emulation")]
+// Compiled under `cfg(test)` as well as the feature: its tests pin the unlock
+// wire format, and gating the whole module on a non-default feature meant CI
+// (which builds with default features) never ran them.
+#[cfg(any(feature = "emulation", test))]
 mod cdb;
 mod error;
 mod platform;
@@ -22,7 +25,7 @@ use crate::{DriveId, UnlockCtx, UnlockError, Unlocked, Unlocker};

 // ── Public profile catalog ──────────────────────────────────────────────────
 //
-// The catalog of drives the LibreDrive unlocker recognizes is the one piece of
+// The catalog of drives the MT1959 unlocker recognizes is the one piece of
 // ld worth exposing publicly: it answers "is this drive supported?" without
 // unlocking, and the bdemu test-emulator reads it to impersonate a supported
 // drive. The unlock *mechanism* (firmware blobs, upload sequence, CDB wire
@@ -30,7 +33,7 @@ use crate::{DriveId, UnlockCtx, UnlockError, Unlocked, Unlocker};

 pub use profile::{DriveProfile as Profile, Identity, Platform, ProfileMatch, Profiles};

-/// The bundled LibreDrive profile catalog (parsed once, process-cached), or
+/// The bundled MT1959 profile catalog (parsed once, process-cached), or
 /// `None` if the embedded JSON fails to parse (a build-time bug). Pair with
 /// [`Profiles::get`] to look up a specific drive:
 /// `freemkv_unlock::ld::profiles().and_then(|p| p.get(&drive_id))`.
@@ -51,17 +54,17 @@ pub fn profile(drive_id: &DriveId) -> Option<ProfileMatch> {
 #[cfg(feature = "emulation")]
 pub use cdb::{UNLOCK_MARKER, is_unlock_read_buffer};

-/// The LibreDrive unlocker. `pub(crate)` — clients reach it only through
+/// The MT1959 unlocker. `pub(crate)` — clients reach it only through
 /// [`crate::all_unlockers`], never by name (the locked-design contract).
 ///
 /// Matches a drive against the bundled profile database and, on a hit,
 /// runs the MediaTek MT1959 firmware-unlock (and disc-speed calibration)
 /// handshake over the raw SCSI transport.
-pub(crate) struct LibreDrive;
+pub(crate) struct Mt1959Unlocker;

-impl LibreDrive {
+impl Mt1959Unlocker {
    pub(crate) fn new() -> Self {
-        LibreDrive
+        Mt1959Unlocker
    }
 }

@@ -69,29 +72,48 @@ impl LibreDrive {
 /// drive-info "is this drive supported?" display), or `None`. A pure profile
 /// lookup — does NOT touch the drive or unlock anything.
 pub(crate) fn firmware_name(id: &DriveId) -> Option<&'static str> {
-    profile::find_bundled(id).map(|_| "LibreDrive")
+    profile::find_bundled(id).map(|_| "MT1959")
 }

-impl LibreDrive {
+impl Mt1959Unlocker {
    /// Read the OEM Volume ID via the matched profile's vendor CDB.
    ///
+    /// Takes the profile the caller ALREADY matched rather than re-running
+    /// `find_bundled`: the catalog is 206 entries and drive-prep used to scan it
+    /// twice per drive (once here, once in `firmware_unlock`) for the same
+    /// answer.
+    ///
    /// `Ok(Some(vid))` on a well-formed 36-byte response (signature `00 22 00`,
    /// VID at `[4..20]`); `Ok(None)` when there is no OEM-VID CDB or the response
-    /// is short / bad-signature (the drive is still unlocked, just no VID); `Err`
-    /// only on a transport fault.
-    fn read_oem_vid(&self, scsi: &mut dyn ScsiTransport, id: &DriveId) -> Result<Option<[u8; 16]>> {
+    /// is short / bad-signature / drive-rejected (the drive is still unlocked,
+    /// just no VID); `Err` only on a transport fault.
+    fn read_oem_vid(
+        &self,
+        scsi: &mut dyn ScsiTransport,
+        profile: &profile::DriveProfile,
+    ) -> Result<Option<[u8; 16]>> {
        const RESPONSE_LEN: usize = 36;
        const EXPECTED_HEADER: [u8; 3] = [0x00, 0x22, 0x00];

-        let Some(m) = profile::find_bundled(id) else {
-            return Ok(None);
-        };
-        let Some(cdb) = m.profile.read_vid_cdb else {
+        let Some(cdb) = profile.read_vid_cdb else {
            return Ok(None);
        };

        let mut buf = vec![0u8; RESPONSE_LEN];
        let result = scsi.execute(&cdb, DataDirection::FromDevice, &mut buf, 5_000)?;
+        // Per the transport contract a drive sense arrives as `Ok` with a
+        // non-zero `status`, NOT as `Err`. Without this check a CHECK CONDITION
+        // would be read as a successful 36-byte response and the caller's own
+        // zero fill parsed as a Volume ID.
+        if result.status != 0 {
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase = "oem_vid_check_condition",
+                status = result.status,
+                "OEM VID CDB returned a drive sense"
+            );
+            return Ok(None);
+        }
        if result.bytes_transferred < RESPONSE_LEN {
            tracing::warn!(
                target: "freemkv::disc",
@@ -116,8 +138,8 @@ impl LibreDrive {
    }
 }

-impl LibreDrive {
-    /// The MediaTek firmware unlock. Because LibreDrive removes AACS bus
+impl Mt1959Unlocker {
+    /// The MediaTek firmware unlock. Because the MT1959 unlocker removes AACS bus
    /// encryption AT THE DRIVE (the unlocked drive serves CLEAR content), this ONE
    /// operation satisfies BOTH the drive-features and the bus-removal capability
    /// — so `unlock_features` and `unlock_bus` both delegate here. The result
@@ -141,13 +163,55 @@ impl LibreDrive {
        }
        let is_variant_b = matches!(m.platform, profile::Platform::Mt1959B);
        use platform::PlatformDriver;
-        let mut mt = platform::mt1959::Mt1959::new(m.profile, is_variant_b);
+        let mut mt = platform::mt1959::Mt1959::new(m.profile.clone(), is_variant_b);
        // A transport fault → UnlockError::Transport; any other firmware failure
        // → NotApplicable (via From<error::Error>).
        mt.init(scsi)?;
-        // Prime the per-region speed table (best-effort — must not fail the unlock).
-        let _ = mt.probe_disc(scsi);
-        let vid = self.read_oem_vid(scsi, id)?;
+        // `init` only proves the handshake COMPLETED — `do_unlock` returns Ok on
+        // a response that carried the per-drive signature but not both firmware
+        // markers. Only `is_unlocked()` means the drive actually reached the
+        // extended-access state and serves clear content. Reporting
+        // `drive_unlocked: true` off `init` alone told the consumer the bus was
+        // clear on a half-unlocked drive, which suppressed the cert-auth
+        // fallback and shipped ciphertext at rc=0. A partial unlock must fall
+        // through to the next unlocker.
+        if !mt.is_unlocked() {
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase = "firmware_unlock_incomplete",
+                "firmware handshake completed but the drive is not in the extended-access state; falling through"
+            );
+            return Err(UnlockError::NotApplicable);
+        }
+        // Prime the per-region speed table. Best-effort — it must not fail the
+        // unlock — but NOT silent: speed calibration can fail completely, and an
+        // unlogged `let _ =` made a fully-failed calibration indistinguishable
+        // from a successful one in the rip log.
+        if let Err(e) = mt.probe_disc(scsi) {
+            // A transport fault here is a DEAD BUS, not a speed-calibration miss.
+            // The rest of this path (`read_oem_vid`) is a no-op for the 140/206
+            // profiles that carry no `read_vid_cdb`, so it never touches the bus
+            // again — meaning this swallowed fault was the ONLY dead-bus signal,
+            // and warn-and-continue turned it into `Ok(Unlocked{drive_unlocked:
+            // true})`: a dead bus rendered as a fully-unlocked drive (the flagship
+            // failure-that-looks-like-success). A genuine calibration miss (drive
+            // sense / short reply) still continues on the default speed table.
+            if e.is_transport_failure() {
+                tracing::warn!(
+                    target: "freemkv::disc",
+                    phase = "probe_disc_transport_fault",
+                    "transport fault during disc speed calibration; aborting"
+                );
+                return Err(UnlockError::Transport);
+            }
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase = "probe_disc_failed",
+                transport_failure = false,
+                "disc speed calibration failed; continuing with the drive's default speed table"
+            );
+        }
+        let vid = self.read_oem_vid(scsi, &m.profile)?;
        Ok(Unlocked {
            vid,
            bus_key: None,
@@ -156,12 +220,12 @@ impl LibreDrive {
    }
 }

-impl Unlocker for LibreDrive {
+impl Unlocker for Mt1959Unlocker {
    fn name(&self) -> &'static str {
-        "LibreDrive"
+        "MT1959"
    }

-    /// LibreDrive provides drive features (riplock/speed, OEM VID) — and, because
+    /// Mt1959Unlocker provides drive features (riplock/speed, OEM VID) — and, because
    /// its firmware unlock serves clear content, bus removal comes free with it.
    fn unlock_features(
        &self,
@@ -171,7 +235,7 @@ impl Unlocker for LibreDrive {
        self.firmware_unlock(scsi, ctx)
    }

-    /// Same firmware code as [`unlock_features`]: LibreDrive removes the bus at
+    /// Same firmware code as [`unlock_features`]: Mt1959Unlocker removes the bus at
    /// the drive. In practice the consumer skips this because drive-prep already
    /// set `drive_unlocked`; it's here for completeness / a bus-first call order.
    fn unlock_bus(
@@ -235,16 +299,21 @@ mod tests {
        }
    }

-    /// A well-formed 36-byte response (signature 00 22 00, VID at [4..20]) parses
-    /// to `Some(vid)`.
-    #[test]
-    fn read_oem_vid_parses_well_formed_response() {
+    /// The bundled profile of the fixture drive (the one carrying a real
+    /// `read_vid_cdb`).
+    fn known_vid_profile() -> profile::DriveProfile {
        let m = profile::find_bundled(&known_vid_drive_id()).expect("profile match");
        assert!(
            m.profile.read_vid_cdb.is_some(),
            "test fixture drive must carry an OEM VID CDB"
        );
+        m.profile
+    }

+    /// A well-formed 36-byte response (signature 00 22 00, VID at [4..20]) parses
+    /// to `Some(vid)`.
+    #[test]
+    fn read_oem_vid_parses_well_formed_response() {
        let mut payload = vec![0u8; 36];
        payload[0..3].copy_from_slice(&[0x00, 0x22, 0x00]);
        let vid = [0x3Cu8; 16];
@@ -253,8 +322,8 @@ mod tests {
            payload,
            bytes_transferred: 36,
        };
-        let got = LibreDrive::new()
-            .read_oem_vid(&mut t, &known_vid_drive_id())
+        let got = Mt1959Unlocker::new()
+            .read_oem_vid(&mut t, &known_vid_profile())
            .expect("parse ok");
        assert_eq!(got, Some(vid), "VID parsed from [4..20]");
    }
@@ -266,8 +335,8 @@ mod tests {
            payload: vec![0u8; 36],
            bytes_transferred: 20,
        };
-        let got = LibreDrive::new()
-            .read_oem_vid(&mut t, &known_vid_drive_id())
+        let got = Mt1959Unlocker::new()
+            .read_oem_vid(&mut t, &known_vid_profile())
            .expect("short response is Ok(None)");
        assert_eq!(got, None);
    }
@@ -281,25 +350,62 @@ mod tests {
            payload,
            bytes_transferred: 36,
        };
-        let got = LibreDrive::new()
-            .read_oem_vid(&mut t, &known_vid_drive_id())
+        let got = Mt1959Unlocker::new()
+            .read_oem_vid(&mut t, &known_vid_profile())
            .expect("bad header is Ok(None)");
        assert_eq!(got, None);
    }

-    /// A drive with no matching profile → `read_oem_vid` is `Ok(None)`.
+    /// Catches dropping the `result.status` check: a CHECK CONDITION arrives as
+    /// `Ok` per the transport contract, so without it the caller's zero-filled
+    /// buffer is parsed as a real 36-byte response.
    #[test]
-    fn read_oem_vid_no_profile_is_none() {
+    fn read_oem_vid_check_condition_is_none_not_a_vid() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let mut t = MockTransport::always(Reply::illegal_request());
+        let got = Mt1959Unlocker::new()
+            .read_oem_vid(&mut t, &known_vid_profile())
+            .expect("a drive sense is not a transport fault");
+        assert_eq!(got, None, "a CHECK CONDITION must never yield a VID");
+    }
+
+    /// Catches swallowing a transport fault in the OEM-VID read: a dead bus must
+    /// propagate (→ `UnlockError::Transport`), never become `Ok(None)`.
+    #[test]
+    fn read_oem_vid_transport_fault_propagates() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let mut t = MockTransport::always(Reply::TransportFault);
+        let err = Mt1959Unlocker::new()
+            .read_oem_vid(&mut t, &known_vid_profile())
+            .expect_err("a dead bus must not be Ok(None)");
+        assert!(err.is_transport_failure());
+        assert_eq!(UnlockError::from(err), UnlockError::Transport);
+    }
+
+    /// A profile with no OEM-VID CDB → `Ok(None)` without touching the drive.
+    #[test]
+    fn read_oem_vid_no_cdb_is_none() {
+        let mut p = known_vid_profile();
+        p.read_vid_cdb = None;
        let mut t = FakeTransport {
            payload: vec![0u8; 36],
            bytes_transferred: 36,
        };
-        let got = LibreDrive::new()
-            .read_oem_vid(&mut t, &make_drive_id("FAKE-VND", "9.99", "XX12345", ""))
-            .expect("no profile is Ok(None)");
+        let got = Mt1959Unlocker::new()
+            .read_oem_vid(&mut t, &p)
+            .expect("no CDB is Ok(None)");
        assert_eq!(got, None);
    }

+    /// Public catalog accessors: `profiles()` returns the bundled catalog and
+    /// `profile()` is `profiles().and_then(get)` for a known drive.
+    #[test]
+    fn public_catalog_accessors_find_the_bundled_fixture_drive() {
+        assert!(super::profiles().is_some(), "bundled catalog must parse");
+        let m = super::profile(&known_vid_drive_id()).expect("known fixture drive matches");
+        assert!(m.profile.read_vid_cdb.is_some());
+    }
+
    /// `unlock_features` on a drive with no matching profile → `NotApplicable`
    /// (fall through), short-circuiting before any firmware handshake.
    #[test]
@@ -308,7 +414,7 @@ mod tests {
            payload: vec![0u8; 36],
            bytes_transferred: 36,
        };
-        let err = LibreDrive::new()
+        let err = Mt1959Unlocker::new()
            .unlock_features(
                &mut t,
                &ctx(&make_drive_id("FAKE-VND", "9.99", "XX12345", "")),
@@ -316,4 +422,205 @@ mod tests {
            .expect_err("no profile → NotApplicable");
        assert_eq!(err, UnlockError::NotApplicable);
    }
+
+    /// THE defect-1 test. The drive answers every unlock READ_BUFFER with a
+    /// response carrying the per-drive signature and the primary firmware marker
+    /// but NOT the secondary one — `do_unlock` returns `Ok` and `init()`
+    /// succeeds, yet the drive is NOT in the extended-access state. Reporting
+    /// `drive_unlocked: true` here suppresses the cert-auth fallback. Catches
+    /// removing the `is_unlocked()` gate in `firmware_unlock`.
+    #[test]
+    fn half_unlocked_drive_falls_through_instead_of_claiming_unlocked() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let id = known_vid_drive_id();
+        let sig = profile::find_bundled(&id)
+            .expect("profile")
+            .profile
+            .signature;
+
+        // 64-byte unlock response: signature + primary marker "MMkv" at [12..16],
+        // secondary marker at [16..20] left zeroed.
+        let mut resp = vec![0u8; 64];
+        resp[0..4].copy_from_slice(&sig);
+        resp[12..16].copy_from_slice(&[0x4D, 0x4D, 0x6B, 0x76]);
+
+        let mut t = MockTransport::always(Reply::good(resp));
+        let err = Mt1959Unlocker::new()
+            .unlock_features(&mut t, &ctx(&id))
+            .expect_err("a half-unlocked drive must fall through to cert-auth");
+        assert_eq!(err, UnlockError::NotApplicable);
+    }
+
+    /// The whole-unlock happy path still reports `drive_unlocked` when BOTH
+    /// firmware markers are present — the `is_unlocked()` gate must not have
+    /// made a genuinely unlocked drive fall through.
+    #[test]
+    fn fully_unlocked_drive_reports_drive_unlocked() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let id = known_vid_drive_id();
+        let sig = profile::find_bundled(&id)
+            .expect("profile")
+            .profile
+            .signature;
+
+        let mut resp = vec![0u8; 64];
+        resp[0..4].copy_from_slice(&sig);
+        resp[12..16].copy_from_slice(&[0x4D, 0x4D, 0x6B, 0x76]);
+        resp[16..20].copy_from_slice(&[0x4C, 0x62, 0x44, 0x72]);
+
+        let mut t = MockTransport::always(Reply::good(resp));
+        let u = Mt1959Unlocker::new()
+            .unlock_features(&mut t, &ctx(&id))
+            .expect("both markers → unlocked");
+        assert!(u.drive_unlocked);
+    }
+
+    /// THE probe-disc dead-bus test. The drive unlocks fully (both firmware
+    /// markers), then the bus DIES during disc-speed calibration. `probe_disc`
+    /// used to be warn-and-continued regardless of the fault, and — because the
+    /// 140/206 profiles without a `read_vid_cdb` never touch the bus again — a
+    /// dead bus was reported as `Ok(Unlocked{drive_unlocked:true})`: a dead bus
+    /// rendered as a successful unlock (the flagship failure-that-looks-like-
+    /// success). `firmware_unlock` must now abort with `Transport`.
+    /// MUTATION: reverting the `if e.is_transport_failure()` return in
+    /// `firmware_unlock` (warn-and-continue), OR flattening the probe loops'
+    /// transport classification, makes this go red.
+    #[test]
+    fn transport_fault_during_probe_disc_is_transport_not_a_successful_unlock() {
+        let id = known_vid_drive_id();
+        let sig = profile::find_bundled(&id)
+            .expect("profile")
+            .profile
+            .signature;
+
+        // A drive that unlocks fully but whose bus dies on the speed probe.
+        struct ProbeFaultsDrive {
+            resp: Vec<u8>,
+        }
+        impl ScsiTransport for ProbeFaultsDrive {
+            fn execute(
+                &mut self,
+                cdb: &[u8],
+                _dir: DataDirection,
+                data: &mut [u8],
+                _timeout_ms: u32,
+            ) -> crate::scsi::Result<ScsiResult> {
+                // READ_BUFFER (0x3C) / SUB_CMD_PROBE (0x14) is the speed probe.
+                if cdb.first() == Some(&0x3C) && cdb.get(3) == Some(&0x14) {
+                    return Err(crate::scsi::ScsiError {
+                        status: crate::scsi::SCSI_STATUS_TRANSPORT_FAILURE,
+                        sense: None,
+                    });
+                }
+                let n = self.resp.len().min(data.len());
+                data[..n].copy_from_slice(&self.resp[..n]);
+                Ok(ScsiResult {
+                    status: 0,
+                    bytes_transferred: n,
+                    sense: [0u8; 32],
+                })
+            }
+        }
+
+        let mut resp = vec![0u8; 64];
+        resp[0..4].copy_from_slice(&sig);
+        resp[12..16].copy_from_slice(&[0x4D, 0x4D, 0x6B, 0x76]); // primary marker
+        resp[16..20].copy_from_slice(&[0x4C, 0x62, 0x44, 0x72]); // secondary marker
+        let mut t = ProbeFaultsDrive { resp };
+
+        let err = Mt1959Unlocker::new()
+            .unlock_features(&mut t, &ctx(&id))
+            .expect_err("a dead bus during probe must abort, not report success");
+        assert_eq!(err, UnlockError::Transport);
+    }
+
+    /// A drive-sense (not a dead bus) rejecting the speed probe is a genuine
+    /// calibration miss, not a transport fault — `firmware_unlock` must
+    /// warn-and-continue on the drive's default speed table, still reporting a
+    /// full unlock. The non-transport sibling of
+    /// `transport_fault_during_probe_disc_is_transport_not_a_successful_unlock`.
+    #[test]
+    fn drive_sense_during_probe_disc_still_reports_a_successful_unlock() {
+        let id = known_vid_drive_id();
+        let sig = profile::find_bundled(&id)
+            .expect("profile")
+            .profile
+            .signature;
+
+        let mut resp = vec![0u8; 64];
+        resp[0..4].copy_from_slice(&sig);
+        resp[12..16].copy_from_slice(&[0x4D, 0x4D, 0x6B, 0x76]); // primary marker
+        resp[16..20].copy_from_slice(&[0x4C, 0x62, 0x44, 0x72]); // secondary marker
+
+        struct ProbeSenseDrive {
+            resp: Vec<u8>,
+        }
+        impl ScsiTransport for ProbeSenseDrive {
+            fn execute(
+                &mut self,
+                cdb: &[u8],
+                _dir: DataDirection,
+                data: &mut [u8],
+                _timeout_ms: u32,
+            ) -> crate::scsi::Result<ScsiResult> {
+                // READ_BUFFER (0x3C) / SUB_CMD_PROBE (0x14) is the speed probe.
+                if cdb.first() == Some(&0x3C) && cdb.get(3) == Some(&0x14) {
+                    return Ok(ScsiResult {
+                        status: 0x02,
+                        bytes_transferred: 0,
+                        sense: [0u8; 32],
+                    });
+                }
+                let n = self.resp.len().min(data.len());
+                data[..n].copy_from_slice(&self.resp[..n]);
+                Ok(ScsiResult {
+                    status: 0,
+                    bytes_transferred: n,
+                    sense: [0u8; 32],
+                })
+            }
+        }
+        let mut t = ProbeSenseDrive { resp };
+        let u = Mt1959Unlocker::new()
+            .unlock_features(&mut t, &ctx(&id))
+            .expect("a calibration miss must not fail the whole unlock");
+        assert!(u.drive_unlocked);
+    }
+
+    /// `unlock_bus` is the same firmware code as `unlock_features` (bus removal
+    /// comes free with the drive unlock) — pins that the trait method actually
+    /// delegates rather than being an accidental no-op stub.
+    #[test]
+    fn unlock_bus_delegates_to_the_same_firmware_unlock() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let id = known_vid_drive_id();
+        let sig = profile::find_bundled(&id)
+            .expect("profile")
+            .profile
+            .signature;
+
+        let mut resp = vec![0u8; 64];
+        resp[0..4].copy_from_slice(&sig);
+        resp[12..16].copy_from_slice(&[0x4D, 0x4D, 0x6B, 0x76]);
+        resp[16..20].copy_from_slice(&[0x4C, 0x62, 0x44, 0x72]);
+
+        let mut t = MockTransport::always(Reply::good(resp));
+        let u = Mt1959Unlocker::new()
+            .unlock_bus(&mut t, &ctx(&id))
+            .expect("unlock_bus runs the same firmware handshake");
+        assert!(u.drive_unlocked);
+    }
+
+    /// Catches classifying a dead bus as "not this unlocker's drive": the very
+    /// first unlock command faulting at the transport layer must abort the
+    /// consumer (`Transport`), not fall through to the next unlocker.
+    #[test]
+    fn transport_fault_during_unlock_is_transport_not_not_applicable() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let mut t = MockTransport::always(Reply::TransportFault);
+        let err = Mt1959Unlocker::new()
+            .unlock_features(&mut t, &ctx(&known_vid_drive_id()))
+            .expect_err("dead bus");
+        assert_eq!(err, UnlockError::Transport);
+    }
 }
@@ -1,4 +1,4 @@
-//! Platform-specific drive unlock + disc probing (LibreDrive internals).
+//! Platform-specific drive unlock + disc probing (Mt1959Unlocker internals).

 pub mod mt1959;

@@ -17,9 +17,49 @@ pub(crate) trait PlatformDriver: Send {
    #[allow(dead_code)]
    fn is_ready(&self) -> bool;

-    /// True if the drive is currently in the extended-access state.
-    #[allow(dead_code)]
+    /// True if the drive is currently in the extended-access state. THE gate
+    /// `Mt1959Unlocker::firmware_unlock` reports `drive_unlocked` from — `init()`
+    /// returning `Ok` only means the handshake completed, not that the drive
+    /// serves clear content.
    fn is_unlocked(&self) -> bool {
        false
    }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::scsi::mock::{MockTransport, Reply};
+
+    /// A minimal driver that takes every `PlatformDriver` default (`is_unlocked`)
+    /// so the shim's dispatch and the default's `false` are both exercised —
+    /// every real driver (`Mt1959`) overrides `is_unlocked`, so without this the
+    /// default body is dead in coverage even though it is reachable code.
+    struct StubDriver;
+
+    impl PlatformDriver for StubDriver {
+        fn init(&mut self, scsi: &mut dyn ScsiTransport) -> Result<()> {
+            scsi.execute(&[0], crate::scsi::DataDirection::None, &mut [], 0)?;
+            Ok(())
+        }
+
+        fn probe_disc(&mut self, scsi: &mut dyn ScsiTransport) -> Result<()> {
+            scsi.execute(&[0], crate::scsi::DataDirection::None, &mut [], 0)?;
+            Ok(())
+        }
+
+        fn is_ready(&self) -> bool {
+            true
+        }
+    }
+
+    #[test]
+    fn default_is_unlocked_is_false_and_trait_methods_dispatch() {
+        let mut drv = StubDriver;
+        let mut scsi = MockTransport::always(Reply::good(vec![]));
+        assert!(drv.init(&mut scsi).is_ok());
+        assert!(drv.probe_disc(&mut scsi).is_ok());
+        assert!(drv.is_ready());
+        assert!(!drv.is_unlocked());
+    }
+}
@@ -43,7 +43,12 @@ pub(super) fn load_firmware(mt: &mut Mt1959, scsi: &mut dyn ScsiTransport) -> Re
    let mut data = firmware.clone();
    scsi.execute(&cdb, DataDirection::ToDevice, &mut data, 30_000)?;

-    // Verify firmware loaded (non-fatal — different buffer_id 0x45)
+    // Verify the firmware loaded (non-fatal — different buffer_id 0x45). There
+    // is no documented expected payload to compare against, so the outcome is
+    // TRACED rather than asserted: discarding it with `let _ =` meant a corrupt
+    // upload proceeded straight into the do_unlock retries with no diagnostic
+    // whatsoever, which is exactly the silent-failure shape this crate exists to
+    // avoid.
    let verify_cdb = [
        super::SCSI_READ_BUFFER,
        super::MODE_A,
@@ -57,12 +62,43 @@ pub(super) fn load_firmware(mt: &mut Mt1959, scsi: &mut dyn ScsiTransport) -> Re
        0x00,
    ];
    let mut verify_resp = [0u8; super::VALIDATE_RESPONSE_SIZE as usize];
-    let _ = scsi.execute(
+    match scsi.execute(
        &verify_cdb,
        DataDirection::FromDevice,
        &mut verify_resp,
        5_000,
-    );
+    ) {
+        Ok(r) if r.status == 0 && r.bytes_transferred == verify_resp.len() => {
+            tracing::debug!(
+                target: "freemkv::disc",
+                phase = "mt1959a_fw_verify_ok",
+                "variant-A firmware verify read returned a full response"
+            );
+        }
+        Ok(r) => {
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase = "mt1959a_fw_verify_bad",
+                status = r.status,
+                bytes_transferred = r.bytes_transferred,
+                "variant-A firmware verify read did not return a full good response"
+            );
+        }
+        // A dead bus mid-upload must abort, not be swallowed into the unlock
+        // retries below.
+        Err(e) => {
+            let err = crate::ld::error::Error::from(e);
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase = "mt1959a_fw_verify_failed",
+                transport_failure = err.is_transport_failure(),
+                "variant-A firmware verify read failed"
+            );
+            if err.is_transport_failure() {
+                return Err(err);
+            }
+        }
+    }

    // Double unlock after firmware upload. The first establishes the
    // unlock and is fatal on failure; the second is a confirmation pass and
@@ -13,6 +13,47 @@ const FIRMWARE_EXTRA: [u8; 16] = [0; 16];
 /// that drive — real profiles must supply their own (see `DriveProfile`).
 const VENDOR_VERIFY: [u8; 10] = [0xF1, 0x01, 0x02, 0x00, 0x0D, 0x30, 0x01, 0xF3, 0xAD, 0x23];

+/// Trace the outcome of a best-effort firmware-upload step and swallow
+/// everything EXCEPT a transport fault. These steps are advisory (the unlock
+/// retries below are the real gate) but their results were previously thrown
+/// away entirely, so a firmware upload could fail end to end and leave nothing
+/// in the log to say so — and a dead bus kept the sequence running.
+fn trace_step(phase: &'static str, r: crate::scsi::Result<crate::scsi::ScsiResult>) -> Result<()> {
+    match r {
+        Ok(res) if res.status == 0 => {
+            tracing::debug!(
+                target: "freemkv::disc",
+                phase,
+                bytes_transferred = res.bytes_transferred,
+                "firmware upload step ok"
+            );
+            Ok(())
+        }
+        Ok(res) => {
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase,
+                status = res.status,
+                "firmware upload step returned a drive sense"
+            );
+            Ok(())
+        }
+        Err(e) => {
+            let err = crate::ld::error::Error::from(e);
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase,
+                transport_failure = err.is_transport_failure(),
+                "firmware upload step failed"
+            );
+            if err.is_transport_failure() {
+                return Err(err);
+            }
+            Ok(())
+        }
+    }
+}
+
 pub(super) fn load_firmware(mt: &mut Mt1959, scsi: &mut dyn ScsiTransport) -> Result<()> {
    let firmware = &mt.profile.firmware;
    if firmware.is_empty() {
@@ -58,12 +99,15 @@ pub(super) fn load_firmware(mt: &mut Mt1959, scsi: &mut dyn ScsiTransport) -> Re
        0x00,
    ];
    let mut meta_resp = [0u8; 16];
-    let _ = scsi.execute(
-        &read_meta_cdb,
-        DataDirection::FromDevice,
-        &mut meta_resp,
-        5_000,
-    );
+    trace_step(
+        "mt1959b_fw_meta",
+        scsi.execute(
+            &read_meta_cdb,
+            DataDirection::FromDevice,
+            &mut meta_resp,
+            5_000,
+        ),
+    )?;

    // Step 3: Write extra firmware data (all zeros)
    let write_extra_cdb = [
@@ -79,14 +123,24 @@ pub(super) fn load_firmware(mt: &mut Mt1959, scsi: &mut dyn ScsiTransport) -> Re
        0x00,
    ];
    let mut data2 = FIRMWARE_EXTRA.to_vec();
-    let _ = scsi.execute(&write_extra_cdb, DataDirection::ToDevice, &mut data2, 5_000);
+    trace_step(
+        "mt1959b_fw_extra",
+        scsi.execute(&write_extra_cdb, DataDirection::ToDevice, &mut data2, 5_000),
+    )?;

    // Step 4: Vendor verify (0xF1 — B-only, not standard SCSI). PER-DRIVE: take
    // it from the profile (39 distinct values across the 140 B drives). The
    // const is only a legacy fallback — it carries one drive's token.
+    // The result used to be discarded with `let _ =` despite the comment calling
+    // this a verify step: a corrupt upload proceeded straight to the do_unlock
+    // retries with no diagnostic. There is no documented expected payload, so
+    // the outcome is TRACED; only a dead bus aborts.
    let verify_cdb = mt.profile.fw_verify_cdb.unwrap_or(VENDOR_VERIFY);
    let mut dummy = [0u8; 0];
-    let _ = scsi.execute(&verify_cdb, DataDirection::None, &mut dummy, 5_000);
+    trace_step(
+        "mt1959b_fw_verify",
+        scsi.execute(&verify_cdb, DataDirection::None, &mut dummy, 5_000),
+    )?;

    // Step 5: Unlock retries (up to 5, then a final fatal attempt). On a
    // successful unlock we issue one confirmation pass; its result is
@@ -94,9 +148,14 @@ pub(super) fn load_firmware(mt: &mut Mt1959, scsi: &mut dyn ScsiTransport) -> Re
    // unlock state, so a hiccup on the redundant confirmation must not fail
    // an otherwise-good unlock.
    for _attempt in 0..5 {
-        if mt.do_unlock(scsi).is_ok() {
-            let _ = mt.do_unlock(scsi);
-            return Ok(());
+        match mt.do_unlock(scsi) {
+            Ok(_) => {
+                let _ = mt.do_unlock(scsi);
+                return Ok(());
+            }
+            // A dead bus will not recover across five more unlock attempts.
+            Err(e) if e.is_transport_failure() => return Err(e),
+            Err(_) => {}
        }
    }
    mt.do_unlock(scsi)?;
@@ -3,7 +3,7 @@
 use crate::ld::error::{Error, Result};
 use serde::Deserialize;

-/// The LibreDrive profile catalog — the set of optical drives the firmware
+/// The Mt1959Unlocker profile catalog — the set of optical drives the firmware
 /// unlocker recognizes, keyed by chipset + variant. Loaded from the bundled
 /// JSON; the public entry point is [`crate::ld::profiles`].
 #[derive(Debug, Deserialize)]
@@ -19,7 +19,7 @@ pub struct Profiles {
 impl Profiles {
    /// The profile matching a drive identity, if this catalog supports that
    /// drive. Two-pass per platform section: exact (incl. firmware date) then a
-    /// looser vendor/revision/vendor-specific match. See [`find_by_drive_id`].
+    /// looser vendor/revision/vendor-specific match. See `find_by_drive_id`.
    pub fn get(&self, drive_id: &crate::DriveId) -> Option<ProfileMatch> {
        find_by_drive_id(self, drive_id)
    }
@@ -41,7 +41,23 @@ pub struct Identity {
 }

 /// Per-drive profile.
-#[derive(Debug, Clone, Deserialize)]
+///
+/// VISIBILITY: only `identity` and `signature` are public — they are what the
+/// catalog is public FOR ("is this drive supported?", and the emulator's
+/// impersonation). Everything below them is unlock MECHANISM: the MediaTek
+/// firmware image and the per-drive vendor CDB templates. `Cargo.toml` says this
+/// crate is never published because it carries drive firmware; re-exporting
+/// `DriveProfile` with a `pub firmware: Vec<u8>` handed that firmware, and every
+/// vendor CDB, to any downstream crate that called `ld::profile()`. They are
+/// `pub(crate)` so the mechanism stays inside the unlocker.
+///
+/// `allow(dead_code)`: this is the on-disk catalog schema, and several captured
+/// CDB templates have no in-crate consumer yet. They were `pub` before, so the
+/// compiler saw the (external) use; making them `pub(crate)` is what exposes
+/// them as unread. Deleting them would silently drop fields from the format the
+/// profile-extraction pipeline emits.
+#[allow(dead_code)]
+#[derive(Clone, Deserialize)]
 pub struct DriveProfile {
    pub identity: Identity,
    /// Expected first 4 bytes of the drive's unlock response — the
@@ -53,7 +69,7 @@ pub struct DriveProfile {
    /// firmware-load step). JSON-encoded as standard base64; empty when
    /// the profile carries no firmware blob.
    #[serde(default, deserialize_with = "deserialize_base64")]
-    pub firmware: Vec<u8>,
+    pub(crate) firmware: Vec<u8>,

    // ── OEM-extended-access CDB templates ──────────────────────────────
    //
@@ -62,39 +78,61 @@ pub struct DriveProfile {
    // in the JSON as lowercase hex strings without separators
    // (e.g. `"3c014410e29100002400"` for a 10-byte CDB).
    #[serde(default)]
-    pub unlock_init_value: u8,
+    pub(crate) unlock_init_value: u8,
    #[serde(default)]
-    pub unlock_response_size: u8,
+    pub(crate) unlock_response_size: u8,

    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub read_vid_cdb: Option<[u8; 10]>,
+    pub(crate) read_vid_cdb: Option<[u8; 10]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub read_disc_keys_cdb: Option<[u8; 10]>,
+    pub(crate) read_disc_keys_cdb: Option<[u8; 10]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_12")]
-    pub drive_nominal_speed_cdb: Option<[u8; 12]>,
+    pub(crate) drive_nominal_speed_cdb: Option<[u8; 12]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_12")]
-    pub set_speed_max_cdb: Option<[u8; 12]>,
+    pub(crate) set_speed_max_cdb: Option<[u8; 12]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub read10_raw_2sec_cdb: Option<[u8; 10]>,
+    pub(crate) read10_raw_2sec_cdb: Option<[u8; 10]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub read10_raw_1sec_cdb: Option<[u8; 10]>,
+    pub(crate) read10_raw_1sec_cdb: Option<[u8; 10]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub read_buffer_verify_cdb: Option<[u8; 10]>,
+    pub(crate) read_buffer_verify_cdb: Option<[u8; 10]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub write_buffer_cdb: Option<[u8; 10]>,
+    pub(crate) write_buffer_cdb: Option<[u8; 10]>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub read_buffer_unlock_cdb: Option<[u8; 10]>,
+    pub(crate) read_buffer_unlock_cdb: Option<[u8; 10]>,
    /// Variant-B vendor verify (0xF1) CDB. PER-DRIVE: 39 distinct values across
    /// the 140 B drives, so it CANNOT be a hardcoded constant. `variant_b`'s old
    /// `VENDOR_VERIFY` const was one drive's token, wrong for the other ~139.
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes_10")]
-    pub fw_verify_cdb: Option<[u8; 10]>,
+    pub(crate) fw_verify_cdb: Option<[u8; 10]>,

    // Per-drive identifier tables — variable-length hex strings.
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes")]
-    pub speed_zone_table: Option<Vec<u8>>,
+    pub(crate) speed_zone_table: Option<Vec<u8>>,
    #[serde(default, deserialize_with = "deserialize_opt_hex_bytes")]
-    pub speed_calc_table: Option<Vec<u8>>,
+    pub(crate) speed_calc_table: Option<Vec<u8>>,
+}
+
+// Hand-written, REDACTING Debug. `DriveProfile` is `pub` and reachable through
+// the public `Profiles` catalog (`ld::bundled` / `ld::profiles`), whose own
+// derived `Debug` would recurse into this one. `Cargo.toml` says this crate is
+// NEVER published because it carries drive firmware; a derived `Debug` would
+// render that firmware image AND every captured per-drive vendor CDB (the unlock
+// MECHANISM) straight into any log. Show only the PUBLIC identity + signature
+// (what the catalog is public FOR); collapse the firmware to a byte length and
+// omit the vendor CDB templates entirely so no mechanism bytes reach a log.
+impl std::fmt::Debug for DriveProfile {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("DriveProfile")
+            .field("identity", &self.identity)
+            .field("signature", &self.signature)
+            .field(
+                "firmware",
+                &format_args!("[{} bytes redacted]", self.firmware.len()),
+            )
+            .field("cdb_templates", &"[redacted]")
+            .finish()
+    }
 }

 /// Chipset + variant — determined by which section the profile was found in.
@@ -266,7 +304,24 @@ pub fn bundled() -> Option<&'static Profiles> {
    use std::sync::OnceLock;
    static CACHE: OnceLock<Option<Profiles>> = OnceLock::new();
    CACHE
-        .get_or_init(|| load_from_str(BUNDLED_PROFILES).ok())
+        .get_or_init(|| match load_from_str(BUNDLED_PROFILES) {
+            Ok(p) => Some(p),
+            // The `None` is cached PERMANENTLY (correctly — the blob is fixed at
+            // compile time), which means a bad shipped profiles.json makes
+            // Mt1959Unlocker report "drive not supported" for every drive for the
+            // life of the process. Unlogged, that is indistinguishable from a
+            // genuinely uncataloged drive; log it once, loudly, at the one place
+            // the parse happens.
+            Err(e) => {
+                tracing::error!(
+                    target: "freemkv::disc",
+                    phase = "bundled_profiles_parse_failed",
+                    error_code = e.code(),
+                    "bundled Mt1959Unlocker profile catalog failed to parse; no drive can match"
+                );
+                None
+            }
+        })
        .as_ref()
 }

@@ -660,6 +715,40 @@ mod tests {
        );
    }

+    /// `DriveProfile`'s `Debug` must NOT render the firmware image or the
+    /// per-drive vendor CDB templates — this crate is unpublished precisely
+    /// because it carries drive firmware, and the profile is reachable through
+    /// the public `Profiles` catalog.
+    /// MUTATION: restoring `#[derive(Debug)]` prints the raw firmware bytes
+    /// (e.g. the 0xEE marker below) and the CDB bytes, so this goes red.
+    #[test]
+    fn drive_profile_debug_redacts_firmware_and_cdbs() {
+        use serde_json::json;
+        let profiles: Profiles = serde_json::from_str(
+            &json!({
+                "mt1959_a": [{
+                    "identity": {"vendor_id":"VIS","product_revision":"1.00",
+                        "vendor_specific":"AA00000","firmware_date":"200001010000"},
+                    "signature":"aabbccdd",
+                    "firmware":"7u7u7u7u", // base64 → six 0xEE bytes
+                    "read_vid_cdb":"3c014410e29100002400"
+                }]
+            })
+            .to_string(),
+        )
+        .unwrap();
+        let s = format!("{:?}", profiles.mt1959_a[0]);
+        // Firmware byte 0xEE renders as `238` under a derived Debug.
+        assert!(!s.contains("238"), "firmware bytes must not appear: {s}");
+        assert!(
+            !s.contains("read_vid_cdb"),
+            "CDB templates must not appear: {s}"
+        );
+        assert!(s.contains("redacted"), "must mark redaction: {s}");
+        // The PUBLIC fields stay visible.
+        assert!(s.contains("VIS"), "identity must remain visible: {s}");
+    }
+
    /// deserialize_hex4 of an empty string must produce [0;4] without error.
    /// This matches `deserialize_hex4`'s explicit early-return for empty strings.
    /// Mutation: treating empty string as an error prevents profiles where signature
@@ -17,11 +17,12 @@ mod css;
 // `ld` is public ONLY for its drive-profile catalog (`ld::profiles` / the
 // `Profiles` object) and, under the `emulation` feature, the unlock-handshake
 // wire format the bdemu test-emulator needs. The unlocker impl itself
-// (`LibreDrive`) is `pub(crate)` — clients still reach unlockers only through
+// (`Mt1959Unlocker`) is `pub(crate)` — clients still reach unlockers only through
 // [`all_unlockers`]. `aacs` and `css` carry no such public catalog, so they
 // stay fully private.
 pub mod ld;
-// `renesis` is public for its `is_renesas` drive-probe; the unlocker impl
+// `renesis` is public for its `is_renesas` drive-probe (which reports a dead
+// bus as `Err(UnlockError::Transport)` rather than "not a Renesas drive"); the unlocker impl
 // (`Renesis`) is `pub(crate)` — reached only through [`all_unlockers`].
 pub mod renesis;

@@ -82,13 +83,30 @@ impl<'a> UnlockCtx<'a> {
 /// What removing bus encryption yielded. `drive_unlocked` means the drive now
 /// serves clear content (firmware route) — equivalent, for the gate, to a cert
 /// `bus_key`.
-#[derive(Debug, Clone, Default)]
+#[derive(Clone, Default)]
 pub struct Unlocked {
    pub vid: Option<[u8; 16]>,
    pub bus_key: Option<[u8; 16]>,
    pub drive_unlocked: bool,
 }

+// Hand-written, REDACTING Debug — `Unlocked` is the public carrier that leaves
+// this crate, and both `bus_key` (the AACS bus key) and `vid` (the Volume ID
+// that feeds VUK derivation) are key material that must never reach a log or a
+// test-failure message in plaintext. The `AacsAuth` / `CertHandshake` siblings
+// already redact; a derived `Debug` here would print the very bytes they hide.
+// Presence is still observable (Some/None) so a log can say WHETHER a key was
+// obtained without revealing WHAT it is.
+impl std::fmt::Debug for Unlocked {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Unlocked")
+            .field("vid", &self.vid.map(|_| "[redacted]"))
+            .field("bus_key", &self.bus_key.map(|_| "[redacted]"))
+            .field("drive_unlocked", &self.drive_unlocked)
+            .finish()
+    }
+}
+
 /// Why an unlock produced no usable result. Only `Transport` is a hard error
 /// (bus dead → consumer aborts); the rest mean "fall through to the next
 /// unlocker".
@@ -114,7 +132,7 @@ pub enum UnlockError {
 /// NOTE: drive tuning (e.g. SET CD SPEED to lift riplock) is deliberately NOT
 /// here — that is the consumer's concern, not bus removal.
 pub trait Unlocker: Send + Sync {
-    /// Short, stable identifier for this unlocker (e.g. "LibreDrive", "AACS",
+    /// Short, stable identifier for this unlocker (e.g. "MT1959", "AACS",
    /// "DVD", "Renesas"). The ONE place a name lives — apps render the unlocker
    /// report from [`all_unlockers`], never hardcoding names, so adding/removing
    /// an unlocker updates every report with no app change.
@@ -122,7 +140,7 @@ pub trait Unlocker: Send + Sync {

    /// Unlock DRIVE FEATURES — riplock/speed, OEM Volume ID, OEM extended-access
    /// reads. The consumer runs this at drive-prep, trying each unlocker until
-    /// one handles the drive. `Ok(_)` = this unlocker handled it (LibreDrive also
+    /// one handles the drive. `Ok(_)` = this unlocker handled it (Mt1959Unlocker also
    /// removes bus encryption at the drive, so its result carries
    /// `drive_unlocked: true`); `Err(NotApplicable)` = not this unlocker's drive;
    /// `Err(Transport)` = dead bus (the consumer aborts). Default: not provided.
@@ -138,7 +156,8 @@ pub trait Unlocker: Send + Sync {
    /// Remove BUS ENCRYPTION for the mounted disc (AACS host-cert handshake, or
    /// CSS scrambled-sector auth). The consumer runs this only when the bus isn't
    /// already clear, trying each unlocker until one handles it. Same `Ok` /
-    /// `Err(NotApplicable)` / `Err(Transport)` contract as [`unlock_features`].
+    /// `Err(NotApplicable)` / `Err(Transport)` contract as
+    /// [`Unlocker::unlock_features`].
    /// Default: not provided.
    fn unlock_bus(
        &self,
@@ -164,9 +183,94 @@ pub fn unlocker_name(drive_id: &DriveId) -> Option<&'static str> {
 /// dir; the consumer never changes.
 pub fn all_unlockers() -> Vec<Box<dyn Unlocker>> {
    vec![
-        Box::new(ld::LibreDrive::new()),
+        Box::new(ld::Mt1959Unlocker::new()),
        Box::new(renesis::Renesis::new()),
        Box::new(aacs::AacsCert::new()),
        Box::new(css::DvdUnlocker::new()),
    ]
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// The dispatch order is a documented contract (`firmware → cert → css`) and
+    /// had NO test: `all_unlockers` is the one place an unlocker is named, and
+    /// the consumer stops at the first that doesn't decline, so reordering this
+    /// list silently changes which unlocker claims a drive. Catches a reorder,
+    /// a rename, and an accidental addition/removal.
+    #[test]
+    fn all_unlockers_dispatch_order_is_firmware_then_cert_then_css() {
+        let names: Vec<&'static str> = all_unlockers().iter().map(|u| u.name()).collect();
+        assert_eq!(names, vec!["MT1959", "Renesas", "AACS", "DVD"]);
+    }
+
+    /// Every unlocker declines by default rather than claiming a capability it
+    /// does not provide — and declines WITHOUT touching the transport, so the
+    /// consumer can iterate the whole registry on any drive.
+    #[test]
+    fn unlockers_decline_capabilities_they_do_not_provide() {
+        struct DeadTransport;
+        impl scsi::ScsiTransport for DeadTransport {
+            fn execute(
+                &mut self,
+                _cdb: &[u8],
+                _dir: scsi::DataDirection,
+                _data: &mut [u8],
+                _timeout_ms: u32,
+            ) -> scsi::Result<scsi::ScsiResult> {
+                panic!("a declining unlocker must not issue a CDB");
+            }
+        }
+        let id = DriveId::default(); // matches no bundled profile
+        let ctx = UnlockCtx::new(&id, DiscKind::Unencrypted, &[]);
+        let mut t = DeadTransport;
+        for u in all_unlockers() {
+            // AACS/DVD provide no drive features; Mt1959Unlocker/Renesas are the
+            // feature unlockers but decline an unknown drive identity.
+            let name = u.name();
+            if name == "AACS" || name == "DVD" {
+                assert_eq!(
+                    u.unlock_features(&mut t, &ctx).unwrap_err(),
+                    UnlockError::NotApplicable,
+                    "{name} must not claim drive features"
+                );
+            }
+            if name == "Renesas" {
+                assert_eq!(
+                    u.unlock_bus(&mut t, &ctx).unwrap_err(),
+                    UnlockError::NotApplicable,
+                    "{name} leaves bus removal to the cert unlocker"
+                );
+            }
+        }
+    }
+
+    /// `unlocker_name` is a PURE lookup — it must answer from the `DriveId`
+    /// alone, and only the identity-keyed unlocker can claim a drive this way.
+    #[test]
+    fn unlocker_name_is_a_pure_identity_lookup() {
+        assert_eq!(unlocker_name(&DriveId::default()), None);
+    }
+
+    /// `Unlocked` is the public carrier that leaves the crate, and its `bus_key`
+    /// and `vid` are key material. Its `Debug` must NOT print those bytes.
+    /// MUTATION: restoring `#[derive(Debug)]` prints the raw byte arrays, so the
+    /// distinctive marker bytes appear in the output and this goes red.
+    #[test]
+    fn unlocked_debug_redacts_key_material() {
+        let u = Unlocked {
+            vid: Some([0xAB; 16]),
+            bus_key: Some([0xCD; 16]),
+            drive_unlocked: true,
+        };
+        let s = format!("{u:?}");
+        // A derived Debug renders `[171, 171, ...]` (0xAB) / `[205, ...]` (0xCD).
+        assert!(!s.contains("171"), "vid bytes must not appear: {s}");
+        assert!(!s.contains("205"), "bus_key bytes must not appear: {s}");
+        assert!(s.contains("[redacted]"), "must mark redaction: {s}");
+        // Presence (Some/None) stays observable.
+        assert!(s.contains("Some"), "must still show a key WAS present: {s}");
+        assert!(s.contains("drive_unlocked: true"));
+    }
+}
@@ -16,23 +16,48 @@ const RB_F1_LEN: usize = 48;
 const RENESAS_MARKER: &[u8] = b"SAT";
 const RENESAS_MARKER_OFFSET: usize = 16;

-/// True if `scsi` is a Renesas-platform drive (Pioneer or HL-DT-ST Renesas).
+/// `Ok(true)` if `scsi` is a Renesas-platform drive (Pioneer or HL-DT-ST
+/// Renesas).
 ///
 /// Issues the vendor READ_BUFFER 0x02/0xF1 probe: a Renesas controller serves a
 /// 48-byte identity block whose bytes `[16..19]` are the ASCII `SAT` interface
-/// tag. A MediaTek drive rejects it (ILLEGAL REQUEST → `Err`), and a transport
-/// fault also yields `Err`; both return `false`. This is the definitive
-/// Renesas-vs-MediaTek split.
-pub fn is_renesas(scsi: &mut dyn ScsiTransport) -> bool {
+/// tag. A MediaTek drive rejects it — as a CHECK CONDITION (`Ok` with a
+/// non-zero status) or, through a non-conforming transport, as an `Err`
+/// carrying a sense — which is `Ok(false)`: not a Renesas drive. This is the
+/// definitive Renesas-vs-MediaTek split.
+///
+/// A TRANSPORT fault is `Err(Transport)`. It used to be folded into the same
+/// `false` as a drive rejection, and because this probe is the first SCSI
+/// command the unlocker issues, a dead bus read as "not a Renesas drive" — the
+/// consumer then walked the remaining unlockers against a bus that was gone.
+pub fn is_renesas(scsi: &mut dyn ScsiTransport) -> std::result::Result<bool, UnlockError> {
    let mut buf = [0u8; RB_F1_LEN];
    match scsi.execute(&RB_F1_CDB, DataDirection::FromDevice, &mut buf, 5_000) {
        Ok(r) => {
            let end = RENESAS_MARKER_OFFSET + RENESAS_MARKER.len();
-            r.status == 0
+            Ok(r.status == 0
                && r.bytes_transferred >= end
-                && &buf[RENESAS_MARKER_OFFSET..end] == RENESAS_MARKER
+                && &buf[RENESAS_MARKER_OFFSET..end] == RENESAS_MARKER)
+        }
+        // Only a senseless transport-failure status is a dead bus; anything
+        // else the transport reports as `Err` is the drive refusing.
+        Err(e) => {
+            if e.status == crate::scsi::SCSI_STATUS_TRANSPORT_FAILURE && e.sense.is_none() {
+                tracing::warn!(
+                    target: "freemkv::disc",
+                    phase = "renesas_probe_transport_fault",
+                    "transport fault on the Renesas identity probe; aborting"
+                );
+                return Err(UnlockError::Transport);
+            }
+            tracing::debug!(
+                target: "freemkv::disc",
+                phase = "renesas_probe_rejected",
+                status = e.status,
+                "Renesas identity probe rejected by the drive; not a Renesas platform"
+            );
+            Ok(false)
        }
-        Err(_) => false,
    }
 }

@@ -60,7 +85,7 @@ impl Unlocker for Renesis {
        scsi: &mut dyn ScsiTransport,
        _ctx: &UnlockCtx,
    ) -> std::result::Result<Unlocked, UnlockError> {
-        if !is_renesas(scsi) {
+        if !is_renesas(scsi)? {
            return Err(UnlockError::NotApplicable);
        }
        tracing::debug!(
@@ -104,7 +129,11 @@ mod tests {
        }
    }

-    /// Rejects the command (a MediaTek drive → ILLEGAL REQUEST → transport `Err`).
+    /// Rejects the command the way a MediaTek drive does: ILLEGAL REQUEST. The
+    /// sense is what distinguishes this from a dead bus — the old fixture sent
+    /// `sense: None`, which is the wire shape of a TRANSPORT fault, and the test
+    /// built on it asserted `NotApplicable`, pinning exactly the
+    /// misclassification this file had.
    struct RejectingTransport;
    impl ScsiTransport for RejectingTransport {
        fn execute(
@@ -114,9 +143,12 @@ mod tests {
            _data: &mut [u8],
            _timeout_ms: u32,
        ) -> Result<ScsiResult> {
+            let mut sense = [0u8; 32];
+            sense[2] = 0x05; // ILLEGAL REQUEST
+            sense[12] = 0x20; // invalid command operation code
            Err(ScsiError {
                status: crate::scsi::SCSI_STATUS_CHECK_CONDITION,
-                sense: None,
+                sense: Some(sense),
            })
        }
    }
@@ -133,13 +165,13 @@ mod tests {
        let mut t = RenesasTransport {
            payload: renesas_payload(),
        };
-        assert!(is_renesas(&mut t));
+        assert!(is_renesas(&mut t).expect("no transport fault"));
    }

    #[test]
    fn is_renesas_false_when_command_rejected() {
        let mut t = RejectingTransport;
-        assert!(!is_renesas(&mut t));
+        assert!(!is_renesas(&mut t).expect("a drive rejection is not a bus fault"));
    }

    #[test]
@@ -148,7 +180,7 @@ mod tests {
        let mut t = RenesasTransport {
            payload: vec![0u8; 48],
        };
-        assert!(!is_renesas(&mut t));
+        assert!(!is_renesas(&mut t).expect("no transport fault"));
    }

    #[test]
@@ -157,7 +189,7 @@ mod tests {
        let mut t = RenesasTransport {
            payload: vec![0x20u8; 8],
        };
-        assert!(!is_renesas(&mut t));
+        assert!(!is_renesas(&mut t).expect("no transport fault"));
    }

    #[test]
@@ -179,6 +211,8 @@ mod tests {
        assert_eq!(u.bus_key, None);
    }

+    /// A drive REJECTION (ILLEGAL REQUEST, with a sense) is "not a Renesas
+    /// drive" → fall through to the next unlocker.
    #[test]
    fn features_not_applicable_on_non_renesas() {
        let mut t = RejectingTransport;
@@ -188,6 +222,35 @@ mod tests {
        assert_eq!(err, UnlockError::NotApplicable);
    }

+    /// The same rejection delivered the way a CONFORMING transport delivers it —
+    /// `Ok` with a CHECK CONDITION status — must reach the same answer. Catches
+    /// dropping the `r.status == 0` check, which would read the probe buffer's
+    /// zero fill as an identity block.
+    #[test]
+    fn check_condition_is_not_a_renesas_drive() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let mut t = MockTransport::always(Reply::illegal_request());
+        assert!(!is_renesas(&mut t).expect("a drive sense is not a bus fault"));
+    }
+
+    /// THE defect-8 test: a dead bus on the FIRST command the unlocker issues
+    /// must abort the consumer, not be reported as "not a Renesas drive".
+    /// Catches restoring the `Err(_) => false` arm.
+    #[test]
+    fn transport_fault_aborts_instead_of_declining() {
+        use crate::scsi::mock::{MockTransport, Reply};
+        let mut t = MockTransport::always(Reply::TransportFault);
+        assert_eq!(is_renesas(&mut t).unwrap_err(), UnlockError::Transport);
+
+        let mut t = MockTransport::always(Reply::TransportFault);
+        let id = crate::DriveId::default();
+        let ctx = UnlockCtx::new(&id, DiscKind::Unknown, &[]);
+        assert_eq!(
+            Renesis::new().unlock_features(&mut t, &ctx).unwrap_err(),
+            UnlockError::Transport
+        );
+    }
+
    #[test]
    fn does_not_provide_bus_removal() {
        // Renesas leaves bus encryption to the cert: unlock_bus is the default.
@@ -98,3 +98,270 @@ pub(crate) fn build_set_cd_speed(read_speed: u16) -> [u8; 12] {
        0x00,
    ]
 }
+
+// ── Test fixture ────────────────────────────────────────────────────────────
+//
+// The crate-wide mock transport. Before this existed, EVERY mock in the crate
+// returned `Ok` with status 0 and a full `bytes_transferred` — so no test could
+// ever exercise the three outcomes the contract actually distinguishes, and a
+// whole class of transport-fault misclassification bugs sat uncaught (a dead bus
+// read as "this unlocker doesn't apply", a zero-filled buffer read as valid
+// drive data). This fixture can express all of them, and is the red-before-green
+// vehicle for the transport-contract fixes across ld / aacs / css / renesis.
+#[cfg(test)]
+#[allow(dead_code)] // a fixture: each helper is used by a subset of the modules
+pub(crate) mod mock {
+    use super::*;
+    use std::collections::VecDeque;
+
+    /// One scripted answer to one `execute()` call.
+    #[derive(Debug, Clone)]
+    pub(crate) enum Reply {
+        /// `Ok` + GOOD status. `payload` is copied into the caller's buffer;
+        /// `bytes_transferred` defaults to the number of bytes copied.
+        Data {
+            payload: Vec<u8>,
+            bytes_transferred: Option<usize>,
+        },
+        /// `Ok` + a NON-ZERO SCSI status (CHECK CONDITION) with a drive sense.
+        /// Per the contract at [`ScsiTransport::execute`] this is NOT a
+        /// transport fault — the caller must inspect `status`, and a caller that
+        /// doesn't will consume the caller's zero-filled buffer as drive data.
+        Sense {
+            status: u8,
+            sense_key: u8,
+            asc: u8,
+            ascq: u8,
+        },
+        /// `Err` with the transport-failure status and no sense — a genuine
+        /// transport-layer fault (bridge crash / disconnect). MUST abort.
+        TransportFault,
+        /// `Err` carrying a real status + parsed sense. This is what a
+        /// NON-conforming transport does (libfreemkv's adapter returns `Err` for
+        /// any non-zero SCSI status); classification must still treat it as a
+        /// drive rejection, not a dead bus.
+        ErrWithSense {
+            status: u8,
+            sense_key: u8,
+            asc: u8,
+            ascq: u8,
+        },
+    }
+
+    impl Reply {
+        /// `Ok`, GOOD status, full transfer of `payload`.
+        pub(crate) fn good(payload: Vec<u8>) -> Reply {
+            Reply::Data {
+                payload,
+                bytes_transferred: None,
+            }
+        }
+        /// `Ok`, GOOD status, but the drive only delivered `n` bytes.
+        pub(crate) fn short(payload: Vec<u8>, n: usize) -> Reply {
+            Reply::Data {
+                payload,
+                bytes_transferred: Some(n),
+            }
+        }
+        /// `Ok`, GOOD status, ZERO bytes delivered — the buffer the caller reads
+        /// is entirely its own zero fill.
+        pub(crate) fn zero_transfer(len: usize) -> Reply {
+            Reply::Data {
+                payload: vec![0u8; len],
+                bytes_transferred: Some(0),
+            }
+        }
+        /// `Ok` + CHECK CONDITION / ILLEGAL REQUEST (0x05, ASC 0x20 invalid
+        /// command) — the ordinary way a drive refuses a vendor command.
+        pub(crate) fn illegal_request() -> Reply {
+            Reply::Sense {
+                status: SCSI_STATUS_CHECK_CONDITION,
+                sense_key: 0x05,
+                asc: 0x20,
+                ascq: 0x00,
+            }
+        }
+        /// `Err` + CHECK CONDITION / ILLEGAL REQUEST — the same drive refusal as
+        /// seen through a non-conforming transport.
+        pub(crate) fn illegal_request_as_err() -> Reply {
+            Reply::ErrWithSense {
+                status: SCSI_STATUS_CHECK_CONDITION,
+                sense_key: 0x05,
+                asc: 0x20,
+                ascq: 0x00,
+            }
+        }
+    }
+
+    fn sense_buf(sense_key: u8, asc: u8, ascq: u8) -> [u8; 32] {
+        let mut b = [0u8; 32];
+        b[2] = sense_key & 0x0F;
+        b[12] = asc;
+        b[13] = ascq;
+        b
+    }
+
+    /// A scripted transport: answers each `execute()` from `script`, falling
+    /// back to `default` once the script runs out, and records every CDB.
+    pub(crate) struct MockTransport {
+        pub(crate) script: VecDeque<Reply>,
+        pub(crate) default: Reply,
+        pub(crate) cdbs: Vec<Vec<u8>>,
+    }
+
+    impl MockTransport {
+        /// Every command gets the same answer.
+        pub(crate) fn always(reply: Reply) -> Self {
+            MockTransport {
+                script: VecDeque::new(),
+                default: reply,
+                cdbs: Vec::new(),
+            }
+        }
+        /// The first N commands follow `script`; the rest get `default`.
+        pub(crate) fn scripted(script: Vec<Reply>, default: Reply) -> Self {
+            MockTransport {
+                script: script.into(),
+                default,
+                cdbs: Vec::new(),
+            }
+        }
+        /// How many CDBs were issued (lets a test assert a dead bus aborted
+        /// instead of retrying).
+        pub(crate) fn calls(&self) -> usize {
+            self.cdbs.len()
+        }
+    }
+
+    impl ScsiTransport for MockTransport {
+        fn execute(
+            &mut self,
+            cdb: &[u8],
+            _direction: DataDirection,
+            data: &mut [u8],
+            _timeout_ms: u32,
+        ) -> Result<ScsiResult> {
+            self.cdbs.push(cdb.to_vec());
+            let reply = self
+                .script
+                .pop_front()
+                .unwrap_or_else(|| self.default.clone());
+            match reply {
+                Reply::Data {
+                    payload,
+                    bytes_transferred,
+                } => {
+                    let n = payload.len().min(data.len());
+                    data[..n].copy_from_slice(&payload[..n]);
+                    Ok(ScsiResult {
+                        status: 0,
+                        bytes_transferred: bytes_transferred.unwrap_or(n),
+                        sense: [0u8; 32],
+                    })
+                }
+                Reply::Sense {
+                    status,
+                    sense_key,
+                    asc,
+                    ascq,
+                } => Ok(ScsiResult {
+                    status,
+                    bytes_transferred: 0,
+                    sense: sense_buf(sense_key, asc, ascq),
+                }),
+                Reply::TransportFault => Err(ScsiError {
+                    status: SCSI_STATUS_TRANSPORT_FAILURE,
+                    sense: None,
+                }),
+                Reply::ErrWithSense {
+                    status,
+                    sense_key,
+                    asc,
+                    ascq,
+                } => Err(ScsiError {
+                    status,
+                    sense: Some(sense_buf(sense_key, asc, ascq)),
+                }),
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use mock::{MockTransport, Reply};
+
+    /// The fixed-format sense layout the whole crate reads its diagnostics off
+    /// (key at byte 2 low nibble, ASC at 12, ASCQ at 13). This file had no test
+    /// at all, so nothing pinned the offsets.
+    #[test]
+    fn sense_parses_at_the_fixed_format_offsets() {
+        let mut buf = [0u8; 32];
+        buf[2] = 0xF5; // sense key is the LOW nibble only
+        buf[12] = 0x24;
+        buf[13] = 0x01;
+        let s = ScsiSense::from_buf(&buf);
+        assert_eq!(s.sense_key, 0x05);
+        assert_eq!(s.asc, 0x24);
+        assert_eq!(s.ascq, 0x01);
+        assert!(s.is_illegal_request());
+
+        buf[2] = 0x02; // NOT READY
+        assert!(!ScsiSense::from_buf(&buf).is_illegal_request());
+    }
+
+    /// SET CD SPEED encodes the read speed big-endian at bytes 2-3 and leaves
+    /// the write speed at 0xFFFF.
+    #[test]
+    fn set_cd_speed_encodes_the_read_speed_big_endian() {
+        let cdb = build_set_cd_speed(0x1234);
+        assert_eq!(cdb[0], SCSI_SET_CD_SPEED);
+        assert_eq!([cdb[2], cdb[3]], [0x12, 0x34]);
+        assert_eq!([cdb[4], cdb[5]], [0xFF, 0xFF]);
+        assert_eq!(build_set_cd_speed(0xFFFF)[2..4], [0xFF, 0xFF]);
+    }
+
+    /// The fixture itself must honour the contract it exists to test: a drive
+    /// sense is `Ok` with a non-zero status, a bus fault is `Err`. If this ever
+    /// drifts, every transport-contract test built on it silently stops testing
+    /// anything.
+    #[test]
+    fn mock_transport_expresses_the_three_contract_outcomes() {
+        let mut t = MockTransport::scripted(
+            vec![
+                Reply::good(vec![0xAB; 4]),
+                Reply::illegal_request(),
+                Reply::zero_transfer(4),
+            ],
+            Reply::TransportFault,
+        );
+        let mut buf = [0u8; 4];
+
+        let r = t
+            .execute(&[0x3C], DataDirection::FromDevice, &mut buf, 0)
+            .expect("data reply is Ok");
+        assert_eq!(r.status, 0);
+        assert_eq!(r.bytes_transferred, 4);
+        assert_eq!(buf, [0xAB; 4]);
+
+        let r = t
+            .execute(&[0x3C], DataDirection::FromDevice, &mut buf, 0)
+            .expect("A DRIVE SENSE IS Ok, NOT Err — the load-bearing contract");
+        assert_eq!(r.status, SCSI_STATUS_CHECK_CONDITION);
+        assert!(ScsiSense::from_buf(&r.sense).is_illegal_request());
+
+        let r = t
+            .execute(&[0x3C], DataDirection::FromDevice, &mut buf, 0)
+            .expect("a zero-length transfer is still Ok");
+        assert_eq!(r.bytes_transferred, 0);
+
+        let e = t
+            .execute(&[0x3C], DataDirection::FromDevice, &mut buf, 0)
+            .expect_err("a transport fault is Err");
+        assert_eq!(e.status, SCSI_STATUS_TRANSPORT_FAILURE);
+        assert!(e.sense.is_none(), "a bus fault carries no drive sense");
+
+        assert_eq!(t.calls(), 4);
+    }
+}