port: withdraw the dual-mono generalisation -- the measurement stands, the rule does not

I argued `highest_rate` had no case because ADV's higher-rate presentation is
dual-mono while its louder one is mono-in-stereo, so the extra bytes buy a
duplicated channel rather than fidelity. The Decoder tested that disc-wide over
the 28 three-stream cues: the stream-3/stream-2 size ratio runs min 0.0778,
median 1.2565, max 2.9163, sd 0.5057, with only 12 of 28 within 15% of 1.0, and
declared rates scatter with them. A 37x spread is not a duplicated channel.

The CHANNEL MEASUREMENT STANDS -- ADV chunk 1 is mono-in-stereo and chunk 2 is
dual-mono at -8.318574, this port's own decode, which the Decoder could not
re-run and did not dispute. What fails is the step from one asset to the format.

NOTHING IN THE EXPORT CHANGES. `loudest` is a per-asset content rule -- it reads
the peak of the streams in front of it -- so a scattering structural ratio cannot
undermine it. What changes is the REASON, in four places: authored/audio.json's
presentation_why, the selector comment in audio.rs, BLOCKED.md's row, and
DECISIONS.md. The honest statement is narrower: `highest_rate` was never refuted,
it was never argued for, and neither is `loudest`. That is why the entry is
marked CHOSEN rather than measured, and why one capture deletes it.

Recorded on the pattern rather than just the instance: this is the third claim of
mine in two iterations that generalised a single-asset observation, after "the
chunks are two stems" and "everything the sequencer paces off rest.t is late".
All three were true of the thing I looked at. The failure is reaching for the
rule a measurement would imply if it held everywhere and writing that down in the
same breath as the measurement.

Also noted, not mine and not affecting export_voice: S12B's three streams are
byte-size identical, and BIRD_224 is three-stream while not being a movie cue.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF

crates/sylpheed-export/src/audio.rs

@@ -623,11 +623,17 @@ pub fn export_voice<S: DiscSource + ?Sized>(
     // WHICH of the equal-duration survivors is a CHOICE, and it lives in
     // `authored/audio.json` rather than here -- see [`Presentation`]. It was
     // `highest_rate` on the Decoder's recommendation until that was withdrawn as
-    // self-contradictory, and the reason it is now `loudest` is a measurement:
-    // `ADV`'s louder presentation is mono-in-stereo while its higher-rate one is
-    // DUAL-MONO, so the extra bytes encode a duplicate channel rather than
-    // fidelity, and the rate difference is explained without appealing to
-    // quality at all.
+    // self-contradictory. `loudest` is a PER-ASSET CONTENT choice and nothing
+    // more: the disc masters its other audio near full scale, and it puts the
+    // two cutscenes' dialogue at comparable levels.
+    //
+    // ⚠️ A structural argument for it — `ADV`'s higher-rate stream is dual-mono,
+    // so its extra bytes encode a duplicated channel rather than fidelity — was
+    // offered here and **does not generalise**. The channel measurement is
+    // `ADV`'s and stands; the inference was tested disc-wide over the 28
+    // three-stream cues and the size ratio runs 0.0778 to 2.9163. Neither rule
+    // has a structural argument behind it, which is exactly why the choice is
+    // authored rather than derived.
     let tied: Vec<usize> = (0..all.len())
         .filter(|&i| !silent.contains(&i) && (longest - lengths[i]).abs() < 0.001)
         .collect();