diff --git a/docs/port/DECISIONS.md b/docs/port/DECISIONS.md
index 883c0c7d..caab3b39 100644
--- a/docs/port/DECISIONS.md
+++ b/docs/port/DECISIONS.md
@@ -3624,3 +3624,46 @@ and whose role is not."*
 provenance is the XMA probe showing `ADV`'s three streams decoding during the
 run, which for an audio question evidences the thing recorded rather than what
 was on screen.
+
+## The stripping control passes — `S00A` is obtainable, and the gate is cleared
+
+The Decoder made this the gate on `S00A`, and it is the right call: `ADV` plays
+itself on boot so it can be captured with `--gpu=null` at 0.96× real time, but
+`S00A` starts ~4.5 s after Ⓐ on a save slot, which needs a **driven** run, which
+needs screens, which rules out `--gpu=null`. So `S00A` is necessarily the 0.70×
+rendered route with ~10 % additive padding — and is only worth a boot if
+stripping that padding is exact.
+
+**It is.** A real music+SFX bed (137.37 s, carrying 454 genuine zero runs of its
+own) had 1 149 holes inserted at 8.37/s to +9.9 % length, matching the observed
+ALSA profile, then was stripped and correlated in the low band:
+
+| | *r* | lag | margin |
+|---|---|---|---|
+| original vs itself — **ceiling** | 1.000 | 0.0 s | +0.141 |
+| **padded** vs original — what padding costs | **0.436** | −12.2 s | **+0.006** |
+| **stripped** vs original — recovered | **1.000** | **0.0 s** | **+0.142** |
+| stripped vs original-also-stripped | 1.000 | 0.0 s | +0.143 |
+
+**Two things worth reading off that table.**
+
+First, **padding at that profile destroys correlation completely** — r 0.436,
+margin +0.006, which is the known-absent regime. That independently confirms, on
+a file whose contents I control, that the earlier captures were unusable for the
+reason claimed rather than for some other reason.
+
+Second, **recovery does not require stripping both sides.** The stripped capture
+matches the *unstripped* source at the ceiling. That matters operationally: the
+port's reference assets never need touching.
+
+⚠️ **What the control does not license.** Stripping removes genuine silence too
+and cannot tell the two apart. On this material the genuine runs total 0.71 s in
+137 s and cost nothing measurable; on material that is mostly silence they would.
+And the whole thing rests on the **substituted-versus-additive** distinction — it
+is valid for Xenia's ALSA padding, which inserts, and it is vandalism on a
+PulseAudio monitor capture, which substitutes. `tools/port/strip-padding` says so
+in its header before it says anything else, because running it on the wrong
+artefact would look like it worked.
+
+Its output is **byte-identical** to the control's own stripping, so the tool and
+the experiment are the same operation rather than two implementations that agree.
diff --git a/tools/port/strip-padding b/tools/port/strip-padding
new file mode 100755
index 00000000..0b09333c
--- /dev/null
+++ b/tools/port/strip-padding
@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+# Remove driver-inserted silence from a capture, exactly.
+#
+#   tools/port/strip-padding in.wav out.wav
+#
+# WHEN THIS IS VALID, AND WHEN IT IS VANDALISM. The distinction is the whole
+# tool and getting it backwards destroys the artefact:
+#
+#   * PulseAudio's monitor SUBSTITUTES silence. It advances on a wall clock and
+#     replaces audio that existed when the producer was late. Information is
+#     gone; deleting the holes compresses time unevenly and repairs nothing.
+#     DO NOT RUN THIS ON A MONITOR CAPTURE.
+#   * Xenia's ALSA writer PADS. It inserts silence between samples the guest
+#     emitted when its ring is empty (`alsa_audio_driver.cc:359`). Nothing is
+#     lost and nothing is overwritten, so removing the padding is EXACT -- it
+#     hands back the contiguous stream the guest produced.
+#
+# CONTROLLED, not argued. A real music+SFX bed (137.37 s, with 454 zero runs of
+# its own) had 1 149 holes inserted at 8.37/s to +9.9 % length, matching the
+# observed ALSA profile, then was stripped:
+#
+#   original vs itself          r 1.000  lag  0.0 s  margin +0.141   [ceiling]
+#   PADDED   vs original        r 0.436  lag -12.2 s margin +0.006   [destroyed]
+#   STRIPPED vs original        r 1.000  lag  0.0 s  margin +0.142   [recovered]
+#
+# Frame counts: original 6 593 984, stripped 6 559 880, and the original stripped
+# of its own genuine zero runs 6 560 044 -- a difference of 164 frames, 3.4 ms in
+# 137 s, from inserted holes abutting genuine ones and merging.
+#
+# ⚠️ It removes GENUINE silence too, and cannot tell the two apart -- that is why
+# the reference above is the unstripped original: recovery does not depend on
+# stripping both sides. On this material the genuine runs total 0.71 s in 137 s
+# and cost nothing measurable. On material that is mostly silence they would.
+set -euo pipefail
+in="${1:?usage: strip-padding IN.wav OUT.wav}"; out="${2:?usage: strip-padding IN.wav OUT.wav}"
+python3 - "$in" "$out" <<'PYEOF'
+import array, struct, sys, wave
+src, dst = sys.argv[1], sys.argv[2]
+w = wave.open(src); ch = w.getnchannels(); rate = w.getframerate()
+if w.getsampwidth() != 2:
+    print("strip-padding: 16-bit PCM only (got %d-bit)" % (w.getsampwidth()*8)); raise SystemExit(2)
+n = w.getnframes(); a = array.array('h'); a.frombytes(w.readframes(n)); w.close()
+MIN = max(1, rate // 1000)          # a gap is a run, not a sample
+sil = bytearray(n)
+for f in range(n):
+    b = f * ch
+    if not any(a[b+c] for c in range(ch)): sil[f] = 1
+keep = array.array('h'); f = 0; removed = 0; holes = 0
+while f < n:
+    s = f
+    if sil[f]:
+        while f < n and sil[f]: f += 1
+        if f - s < MIN: keep.extend(a[s*ch:f*ch])
+        else: removed += f - s; holes += 1
+    else:
+        while f < n and not sil[f]: f += 1
+        keep.extend(a[s*ch:f*ch])
+k = len(keep) // ch
+o = wave.open(dst + ".partial", "wb")   # temp name, renamed on completion
+o.setnchannels(ch); o.setsampwidth(2); o.setframerate(rate)
+o.writeframes(keep.tobytes()); o.close()
+import os; os.replace(dst + ".partial", dst)
+print("%s: %d frames (%.3f s) -> %s: %d frames (%.3f s)"
+      % (src, n, n/rate, dst, k, k/rate))
+print("  removed %d run(s) totalling %.3f s (%.2f %% of the input)"
+      % (holes, removed/rate, 100.0*removed/n))
+PYEOF