CSS DVD mux: per-title key via scan-key reuse + playback-order crack

A CSS DVD whose main title was mis-detected as unencrypted (the up-front
crack scanned the largest cell first and starved its budget in that cell's
clear prefix) muxed scrambled sectors as plaintext at exit 0. CSS leaves
the pack/PES header clear, so an un-descrambled sector muxes as a
structurally-valid but corrupt PES packet with zero loss reported.

decrypt_keys_for_title resolves a DVD title's CSS key two ways:
- Fast path: reuse the scan's cracked key when its crack_span covers this
  title's VTS (no re-read; on a live drive no second bus-auth).
- Crack: on a detection miss or a different VTS, crack from the title's OWN
  extents in a SINGLE scan in natural PLAYBACK ORDER (never largest-first).
  One scan = one CSS-locked early-bail, so a locked title is not re-hammered
  per cell against a live drive (hard rule #2); the 50k-sector budget is the
  same accepted bound the disc-wide scan uses. Cracked -> key; Unencrypted
  -> clear; ScrambledUncracked -> hard-fail.
ensure_title_decryptable hard-fails an uncrackable DVD title even when
detection missed, and passes a title that resolved its OWN valid key
regardless of the disc-wide css_error. descramble_region is unchanged from
v1.5.1 (validated-key seed).

Also rename the unlocker report's DVD entry CSS -> DVD. Bump 1.5.2.

src/mux/resolve.rs

@@ -409,11 +409,23 @@ pub fn input(url: &str, opts: &InputOptions) -> io::Result<Box<dyn crate::pes::S
             // avoids disturbing the mux reader below. 64 sectors is a
             // file-safe batch for an ISO. AACS / single-VTS paths are
             // unchanged (decrypt_keys_for_title short-circuits to decrypt_keys).
-            let (keys, title_is_clear) =
-                match crate::io::file_sector_source::FileSectorSource::open(path) {
-                    Ok(mut crack_reader) => disc.decrypt_keys_for_title(idx, &mut crack_reader, 64),
-                    Err(_) => (disc.decrypt_keys(), false),
-                };
+            //
+            // Only a DVD needs this fresh reader (its per-title crack reads the
+            // title's sectors); AACS / unencrypted resolve their keys from
+            // `decrypt_keys()` with NO read, so we must not open — and fail on —
+            // a probe handle for them (v1.5.1 tolerated an open blip on non-DVDs).
+            // For a DVD the reader IS required, so a failed open is PROPAGATED as
+            // a real, loud, retryable I/O error — never guessed into a
+            // `title_is_clear` verdict: guessing `true` would mux a
+            // detection-miss scrambled DVD keyless (silent garbage); guessing
+            // `false` would falsely hard-fail an unencrypted DVD.
+            let (keys, title_is_clear) = if disc.format == crate::disc::DiscFormat::Dvd {
+                let mut crack_reader = crate::io::file_sector_source::FileSectorSource::open(path)
+                    .map_err(|e| -> io::Error { e.into() })?;
+                disc.decrypt_keys_for_title(idx, &mut crack_reader, 64)
+            } else {
+                (disc.decrypt_keys(), false)
+            };
             // Per-title decrypt gate (parallel to the disc-wide gate above): on
             // a multi-VTS CSS disc, the per-title re-crack may return `None` when
             // the chosen title's VTS could not be re-cracked. Muxing that would