diff --git a/sessions/0021/SESSION-0021.0-TRANSCRIPT-2026-06-26T08-12--2026-06-26T08-20.md b/sessions/0021/SESSION-0021.0-TRANSCRIPT-2026-06-26T08-12--2026-06-26T08-20.md
new file mode 100644
index 0000000..3bb4d6a
--- /dev/null
+++ b/sessions/0021/SESSION-0021.0-TRANSCRIPT-2026-06-26T08-12--2026-06-26T08-20.md
@@ -0,0 +1,88 @@
+# Session 0021.0 — Transcript
+
+> App: human-experience-filter-art
+> Start: 2026-06-26T08-12 (PST)
+> End: 2026-06-26T08-20 (PST)
+> Type: executing-plans (operator-driven hotfix/revision of session 0020's audio feature)
+> Posture: yolo
+> Claude-Session: e0cc053a-41fa-416d-a4f5-493f14984e75
+> Status: FINALIZED
+
+## Launch prompt
+
+> Show video unchecked doesn't turn off the video. Make "show video" just "Video"
+> and have a toggle like "Dev Mode" has. I can't hear any audio when "soundtrack
+> (follows altitude)" is selected. Let's just have Audio as off/on like Video for
+> now and get rid of white noise.
+
+## Pre-state
+
+- Session 0020 had just merged the audio feature to `main` (Visual×Audio split,
+  per-altitude soundtracks, pink white-noise, A/B crossfade). The operator tested it
+  live and reported three issues.
+
+## Session arc
+
+1. **Diagnosis (the key work).** Both reported bugs were reproduced *only* in the
+   operator's real browser — neither appeared in headless Chromium **or** WebKit
+   (installed `playwright install webkit` to test Safari's engine). Root causes:
+   - **Video-off doesn't blank:** `#vid` (`<video>`) and `#paint` (WebGL `<canvas>`)
+     are GPU-composited layers; the `#black` cover had *auto* z-index, so on a real
+     GPU (Safari/Chrome) the video layer can composite *above* it despite DOM order.
+     Headless software-raster hides this.
+   - **No soundtrack audio:** real Safari/iOS unlocks an `<audio>` element only when
+     `play()` is called *synchronously inside* the user gesture; the 0020 gesture
+     played in an async continuation (after `await fetch`), which Chrome allows but
+     Safari blocks. Headless WebKit relaxes autoplay, so it passed.
+   This is the session's main lesson: **Playwright headless relaxes both GPU
+   compositing and autoplay**, so the 0020 E2E couldn't have caught either — real
+   device / by-eye review is required.
+2. **Fixes (branch `session-0021`):**
+   - **Video** + **Audio** are now Dev-Mode-style on/off toggles (`.dev-switch`),
+     wired on `change`. Audio on → soundtrack; **white-noise deferred** (removed from
+     the live control; `AUDIO_SOURCES={off,soundtrack}`; the pure pink-noise
+     machinery + tests stay for later).
+   - Video-off: `.black` gets `z-index:50` + `translateZ(0)` (own layer) **and** the
+     video layers are set `opacity:0` on video-off (belt-and-suspenders blanking).
+   - Safari audio: the tap-to-start gesture now primes both A/B `<audio>` elements
+     **synchronously in-gesture** (set src, vol 0, `play().then(pause)`), unlocking
+     the later async crossfades.
+   - Server: `player/audio.py` resolver + `controls.py`/`state.py` + `/api/alteration`
+     drop white-noise; `build_audio_media.py` stops emitting the noise bed.
+3. **Verify + ship.** Updated unit/contract/E2E tests; rewrote the 3 E2E for the new
+   toggles (click the visible `.dev-switch-track`; wait for the opacity transition).
+   **288 passed, 2 skipped.** Re-verified in **both Chromium and WebKit**: Audio toggle
+   plays `cosmos/pillars.loop.mp3`, video-off sets vid+paint opacity 0 with `#black`
+   shown, zero JS errors; screenshotted the new toggle UI. Merged `session-0021` →
+   `main` and pushed. (Also untracked a stray `docs/.threads/*.json` editor artifact
+   swept in by `git add -A`, and gitignored `.threads/`.)
+
+## Deferred decisions
+
+_No low-confidence calls. All three changes were explicit operator requests; the
+root-cause fixes (GPU z-index/layer-hide; Safari in-gesture unlock) are the standard
+remedies for these well-known browser behaviors._
+
+## Cut state
+
+- `main` @ `fddb6d6` (merge of session-0021), clean, pushed.
+- **288 tests + 3 Playwright E2E pass** (2 skipped: opt-in media integration).
+- White-noise is deferred, not deleted: `tools/pipeline/audio_ops.white_noise_args` +
+  `audio_run.generate_white_noise` + their tests remain; only the live control + the
+  build-script emission were removed.
+- **Unvalidated by this session:** real-device audio (Safari autoplay) and real-GPU
+  video-off — headless can't exercise either; needs the operator's by-ear/by-eye pass.
+
+## Operator plate
+
+- Video + Audio are simple on/off toggles (Dev-Mode style). Audio on = the current
+  altitude's soundtrack. The two real-browser bugs should now be fixed — but please
+  confirm on a real device (especially iPad/Safari).
+- Deferred: white-noise (easy to re-add as a 3rd Audio position), the per-altitude
+  music layer, the networked-control-surface build, Pi renderer.
+
+## Next /goal
+
+```
+/goal by-ear/by-eye review the audio + Video/Audio toggles on a REAL device (esp. iPad/Safari — headless can't validate Safari autoplay or GPU compositing), then source/compose the deferred per-altitude music layer per docs/audio-candidate-pool.md (or re-enable white-noise as a 3rd Audio position if wanted)
+```
diff --git a/sessions/0021/SESSION-0021.0-TRANSCRIPT-2026-06-26T08-12--INPROGRESS.md b/sessions/0021/SESSION-0021.0-TRANSCRIPT-2026-06-26T08-12--INPROGRESS.md
deleted file mode 100644
index dade84c..0000000
--- a/sessions/0021/SESSION-0021.0-TRANSCRIPT-2026-06-26T08-12--INPROGRESS.md
+++ /dev/null
@@ -1,22 +0,0 @@
-# Session 0021.0 — Transcript
-
-> App: human-experience-filter-art
-> Start: 2026-06-26T08-12 (PST)
-> Type: executing-plans
-> Posture: yolo
-> Claude-Session: e0cc053a-41fa-416d-a4f5-493f14984e75
-> Status: **PLACEHOLDER — claimed at session start; finalized at session end.**
->
-> This file reserves session ID 0021 for human-experience-filter-art. The driver replaces this
-> body with the full transcript and renames the file to its final
-> SESSION-0021.0-TRANSCRIPT-2026-06-26T08-12--<end>.md form at session end.
-
-## Launch prompt
-
-_(launch prompt not captured at claim time)_
-
-## Deferred decisions
-
-_Autonomous-mode low-confidence calls the driver made and would have
-liked operator input on. Appended as the session runs; surfaced at
-finalize. Empty if none._