docs(plans): close the listening step on the clip-before-duck fix

Verified by ear 2026-08-09: barely detectable at 1.35x overshoot, heard very
clearly once the chain was pushed. The mechanism is confirmed and the fix does
what it claims; the severity really is conditional on how far past full scale
the chain runs, rather than the original pair having been a bad test.

§4a-1 is fully closed — implemented, tested, mutation-falsified, and now
confirmed audibly.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

plans/audio-review-fixes-handoff.md

@@ -166,10 +166,16 @@ Three judgement calls worth knowing:
   | Chain output peak | Samples changed | Error vs. correct | Verdict |
   | --- | --- | --- | --- |
   | 0.48x | none | -70.0 dB | nothing clamped; 16-bit rounding only |
-  | 1.35x | 2.1% | -25.1 dB | **the author listened and could barely tell** |
+  | 1.35x | 2.1% | -25.1 dB | **barely detectable by ear** |
   | 2.69x | 19.3% | -9.1 dB | plainly audible grit |
   | 4.00x | 48.8% | -3.3 dB | not the same recording |
 
+  **Verified by ear, 2026-08-09.** The author could barely tell the two apart
+  at 1.35x and heard the difference "very clearly" once the chain was pushed.
+  So the mechanism is confirmed real and the fix does what it claims — and the
+  severity genuinely is conditional on overshoot, rather than the pair having
+  been a bad test. This is the listening step §4a-1 was waiting on; it is done.
+
   So: **a chain that stays under full scale is unaffected** — the fix changes
   nothing for it. The bug is real and worth fixing (it destroys data that the
   lane was about to scale down anyway, and there is no reason to accept that),