disc: credit firmware unlock in the bus-encryption gate

The bus-key gate only credited the cert handshake's read_data_key as proof
bus encryption was removed. A firmware unlocker removes it AT THE DRIVE
(serves clear content) and yields no read_data_key — so a SUCCESSFUL
firmware unlock (VID present, read_data_key None) tripped the gate and
blocked ALL key resolution, including the online source. That was the
root cause of live UHD discs reporting "missing keys" after an unlock.

Now a single predicate answers "is bus encryption gone?": never-had-it ||
file/ISO || firmware-unlocked || cert-bus-key. The gate is just
`if !bus_encryption_removed { error }` — no enumerated cases. HandshakeResult
gains `drive_unlocked`, and the read_data_key failure reason is captured so
the warn says WHY the bus key is missing.

Also: reword the first hardware-sense escalation as "fast-fail escalation"
(it is often transient — the drive recovers), reserving "wedge" for a
persistent run; and scrub the product name from core comments (it belongs
only in the unlocker crate).

CHANGELOG.md

@@ -93,6 +93,19 @@ consumers are the in-tree toolchain crates.
   with a per-unit "already-asked-dry" set (still bounded by the fetch budget).
 - **`verify::push_ranges` uses saturating arithmetic** so a corrupt-disc LBA near
   `u32::MAX` can't panic (matches `udf::merge_ranges`).
+- **Audio no longer corrupts at a stream discontinuity.** At a transport-stream
+  discontinuity — a continuity-counter break, an adaptation-field
+  discontinuity_indicator, or a concealed-loss gap — the AC-3 / DTS / TrueHD
+  parsers held a *truncated* partial access unit and spliced the post-gap bytes
+  onto it, manufacturing a corrupt frame (ffmpeg "exponent out of range" /
+  "Failed to decode block code(s)" / "Invalid data found") and, for TrueHD, a
+  non-monotonic timestamp band on multi-segment titles. The video path already
+  resynced via the keyframe gate; the audio parsers now do too — on a
+  discontinuity they drop the un-completable partial and resync on the next
+  syncword, rebasing the timestamp from the post-gap PES. A discontinuity becomes
+  a clean single-frame gap instead of a corrupt splice. Audio has no inter-frame
+  references, so dropping the truncated partial is the complete fix; the approach
+  matches FFmpeg's parser layer and GStreamer's `tsdemux`.
 
 ## [1.1.0]