Fix read-fault misclassification, DTS AMODE channel table, and untestable guards

- resolve_fmts_key_map: distinguish a genuinely-not-FMTS disc from a
  transient live-drive read fault. read_filesystem now returns the new
  Error::UdfNotFilesystem for a deterministic tag/format mismatch (no AVDP,
  no partition descriptor, no FSD); resolve maps only UdfNotFilesystem (fs)
  and UdfNotFound (.tbl absent) to Ok(None), and PROPAGATES DiscRead / other
  I/O faults so a marginal AACS 2.1 disc fails loud instead of silently
  dropping forensic content under a base-Unit-Key-only map.

- DTS_AMODE_CH (mp4/audio.rs): extend 10→16 entries
  {1,2,2,2,2,3,3,4,4,5,6,6,6,7,8,8} (the spec per-AMODE channel table / ETSI TS 102 114) so
  the spec-legal high AMODEs that now pass the decodability gate declare
  their true channelcount (AMODE 13→7, 14/15→8) instead of a truncated 6.

- session.rs resolve_keys "called before scan" guard is now testable:
  from_parts_for_test takes Option<Disc>; added a test that a disc-less
  session returns a clean DeviceNotReady Err rather than panicking.

- mp4/read.rs: a track with samples but a missing/malformed stts (mandatory
  per ISO/IEC 14496-12) is dropped rather than emitting all-zero timestamps,
  matching the existing stco/stsc guards; all-tracks-dropped → Mp4Invalid.

- Remove the inert MuxInput::Iso.key_map field (the Iso path re-derives its
  map inside build_iso_pipeline); the live path keeps Live.key_map.

All four fixes are mutation-verified.

src/mux/mp4/read.rs

@@ -201,6 +201,15 @@ impl<R: Read + Seek> Mp4Reader<R> {
             let durations = find_box(stbl, b"stts")
                 .map(|b| parse_stts(b, n))
                 .unwrap_or_default();
+            if durations.is_empty() {
+                // Samples exist but there is no decoding-time table: `stts` is
+                // mandatory in a valid stbl (ISO/IEC 14496-12 §8.6.1). Without it
+                // every sample would take dur=0 → all-zero, identical timestamps,
+                // collapsing the whole track onto one instant. Drop the track
+                // rather than emit degenerate timing (mirrors the stco/stsc
+                // guards above); an all-tracks-dropped file fails Mp4Invalid below.
+                continue;
+            }
             let ctts = find_box(stbl, b"ctts")
                 .map(|b| parse_ctts(b, n))
                 .unwrap_or_default();
@@ -1216,11 +1225,21 @@ mod tests {
             p.extend_from_slice(&0u32.to_be_bytes()); // sample_desc_idx
             mp4_box(b"stsc", &p)
         };
+        let stts = {
+            // Mandatory time-to-sample box: 1 entry → 1 sample × 1000 ticks.
+            let mut p = Vec::new();
+            p.extend_from_slice(&[0, 0, 0, 0]); // version+flags
+            p.extend_from_slice(&1u32.to_be_bytes()); // entry_count
+            p.extend_from_slice(&1u32.to_be_bytes()); // sample_count
+            p.extend_from_slice(&1000u32.to_be_bytes()); // sample_delta
+            mp4_box(b"stts", &p)
+        };
         let mut stbl = Vec::new();
         stbl.extend_from_slice(&stsd);
         stbl.extend_from_slice(&stsz);
         stbl.extend_from_slice(&stco);
         stbl.extend_from_slice(&stsc);
+        stbl.extend_from_slice(&stts);
         let minf = mp4_box(b"minf", &mp4_box(b"stbl", &stbl));
         let mut mdia = Vec::new();
         mdia.extend_from_slice(&mdhd);
@@ -1319,11 +1338,20 @@ mod tests {
             p.extend_from_slice(&0u32.to_be_bytes()); // sample_desc_idx
             mp4_box(b"stsc", &p)
         };
+        let stts = {
+            let mut p = Vec::new();
+            p.extend_from_slice(&[0, 0, 0, 0]); // version+flags
+            p.extend_from_slice(&1u32.to_be_bytes()); // entry_count
+            p.extend_from_slice(&1u32.to_be_bytes()); // sample_count
+            p.extend_from_slice(&1000u32.to_be_bytes()); // sample_delta
+            mp4_box(b"stts", &p)
+        };
         let mut stbl = Vec::new();
         stbl.extend_from_slice(&stsd);
         stbl.extend_from_slice(&stsz);
         stbl.extend_from_slice(&stco);
         stbl.extend_from_slice(&stsc);
+        stbl.extend_from_slice(&stts);
         let minf = mp4_box(b"minf", &mp4_box(b"stbl", &stbl));
         let mut mdia = Vec::new();
         mdia.extend_from_slice(&mdhd);
@@ -1397,6 +1425,15 @@ mod tests {
             p.extend_from_slice(&0u32.to_be_bytes()); // sample_desc_idx
             mp4_box(b"stsc", &p)
         };
+        let stts = {
+            // Mandatory time-to-sample box: 3 entries' worth via one run (3×1000).
+            let mut p = Vec::new();
+            p.extend_from_slice(&[0, 0, 0, 0]); // version+flags
+            p.extend_from_slice(&1u32.to_be_bytes()); // entry_count
+            p.extend_from_slice(&3u32.to_be_bytes()); // sample_count
+            p.extend_from_slice(&1000u32.to_be_bytes()); // sample_delta
+            mp4_box(b"stts", &p)
+        };
         let mut stbl = Vec::new();
         stbl.extend_from_slice(&stsd);
         stbl.extend_from_slice(&stsz);
@@ -1406,6 +1443,9 @@ mod tests {
         if omit != b"stsc" {
             stbl.extend_from_slice(&stsc);
         }
+        if omit != b"stts" {
+            stbl.extend_from_slice(&stts);
+        }
         let minf = mp4_box(b"minf", &mp4_box(b"stbl", &stbl));
         let mut mdia = Vec::new();
         mdia.extend_from_slice(&mdhd);
@@ -1446,6 +1486,23 @@ mod tests {
         );
     }
 
+    /// A track with samples (`stsz`) but no time-to-sample table (`stts`, mandatory
+    /// per ISO/IEC 14496-12 §8.6.1) must be DROPPED — without it every sample takes
+    /// dur=0, collapsing the whole track onto one instant (all-zero timestamps).
+    /// With it the only track, the file fails `Mp4Invalid`.
+    /// Mutation check: delete the `if durations.is_empty() { continue; }` guard and
+    /// `from_reader` returns `Ok` (all-zero-timestamp samples), flipping this to FAIL.
+    #[test]
+    fn missing_stts_drops_track_all_dropped_is_invalid() {
+        use std::io::Cursor;
+        let moov = mp4_box(b"moov", &audio_trak_missing(b"stts"));
+        let rd = Mp4Reader::from_reader(Cursor::new(moov), "no-stts".into());
+        assert!(
+            rd.is_err(),
+            "a track with stsz but no stts must be dropped; all-dropped → Mp4Invalid"
+        );
+    }
+
     /// Sanity companion: the SAME builder WITH both tables present yields a valid,
     /// indexed single-track file — proving the two Err results above come from the
     /// missing table, not from some unrelated defect in the fixture builder.