re: stripping additive padding is exact -- controlled, and only one side needs it

The page recorded the substituted-versus-additive distinction as unverified, with
the port controlling it. It passes.

A real music and SFX bed of 137.37 s, itself carrying 454 genuine zero runs --
which is what makes it an honest control -- had 1149 holes inserted at 8.37
gaps/s to +9.9 percent length, matching the measured ALSA profile, then stripped:

  original vs itself (ceiling)   r 1.000  lag 0.0 s  margin +0.141
  padded vs original             r 0.436  lag -12.2  margin +0.006
  stripped vs original           r 1.000  lag  0.0   margin +0.142

Two things beyond the yes. It runs the inference forwards: padding at this
profile puts correlation squarely in the known-absent regime on a file whose
contents are controlled, so the earlier captures were unusable for the reason
claimed rather than for some other one -- until now that was reasoning backwards
from a failure to a cause. And only one side needs stripping, since the stripped
capture matches the UNSTRIPPED source at the ceiling, so a capture needs no
preprocessing before being handed over and there is no shared step to get out of
sync on.

The danger is recorded as the part to repeat: stripping removes genuine silence
too and cannot tell the two apart, so it is exact on additive ALSA padding and
vandalism on a PulseAudio monitor capture where the silence replaced real audio.
Running it on the wrong artefact would look like it worked.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QsEPXWVaEpyfudtR6re1Pd

docs/re/audio-capture-alsa-file-tee.md

@@ -186,10 +186,36 @@ means even the 0.70×-real-time rendered capture (9.98 % padded) is usable for
 correlation, where none of the PulseAudio-monitor captures ever were, however
 they were tuned.
 
-⚠️ **Unverified as of writing** — the port is controlling it before relying on
-it, by padding a known source to match and checking the stripped result
-correlates back. The mechanism says it should; the control is what will settle
-it.
+✅ **VERIFIED 2026-08-29.** The port controlled it rather than relying on the
+reasoning: a real music+SFX bed (137.37 s, carrying **454 genuine zero runs of
+its own**, which is what makes it an honest control) had **1 149 holes inserted
+at 8.37 gaps/s to +9.9 % length** — matching the measured ALSA profile — then
+stripped:
+
+| | r | lag | margin |
+|---|---|---|---|
+| original vs itself (ceiling) | 1.000 | 0.0 s | +0.141 |
+| **padded** vs original | **0.436** | −12.2 s | **+0.006** |
+| **stripped** vs original | **1.000** | **0.0 s** | **+0.142** |
+
+Two things beyond the yes:
+
+* ✅ **It runs the inference forwards.** Padding at this profile puts correlation
+  squarely in the known-absent regime (margin +0.006) on a file whose contents
+  are controlled — so the earlier captures were unusable *for the reason claimed*
+  rather than for some other one. Until now that was reasoning backwards from a
+  failure to a cause.
+* ✅ **Only ONE side needs stripping.** The stripped capture matches the
+  **unstripped** source at the ceiling, so a capture needs no preprocessing at
+  all before being handed over — no shared step for two parties to get out of
+  sync on.
+
+🔴 **And the danger, which is the part to repeat:** stripping removes *genuine*
+silence too and cannot tell the two apart. It is **exact on additive ALSA
+padding and vandalism on a PulseAudio monitor capture**, where the silence
+replaced real audio. On mostly-silent material the genuine runs would cost
+something measurable — here they totalled 0.71 s in 137 s and cost nothing.
+⚠️ **Running it on the wrong artefact would look like it worked.**
 
 ⚠️ **Consequence for `check-capture`:** its silence/gap-rate rule was built when
 only *damage* existed, and **cannot distinguish genuine emulator padding from