[laneB] log: M4-B session 4 (audio + visemes)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

logs/laneB.md

@@ -134,3 +134,48 @@ BLOCKED/REQUESTS: none. Verified with a throwaway harness (`_check.html`,
 NEXT: M2 polish complete. Undo already wired (Ctrl+Z). Open for M4 timeline
   work when unlocked (audio tracks on the timeline UI + Web Audio sync, per
   PLAN §5 M4) or any SYNC 3 fixes. Holding until orchestrator flips M4.
+
+## 2026-07-18 session 4 (M4-B: audio + visemes)
+DONE: M4-B all three items.
+  1. Audio rows in tlui from scene.audio[]: one lane per clip below Cameras,
+     green block at the DECODED buffer width (fallback width until decoded),
+     gain <input> in the name column, drag = offset (moveAudio), right-click =
+     delete. 🎵 button reads /assets/tree audio category into a small floating
+     menu → addAudio at the playhead.
+  2. Web Audio draft playback synced to the master clock: lazy AudioContext,
+     decode+cache buffers (/assets/file), _audioStart schedules
+     AudioBufferSourceNodes at (start - time) with per-clip gain, _audioStop on
+     pause/natural-end, user seeks reschedule (_seek helper). step()/render
+     never touch audio — server muxes from scene.audio.
+  3. morphs track kind: _evalMorphs lerps per viseme name → stage.setMorph;
+     importRhubarb(id, json, t0) maps mouthCues → morph keys; tlui shows a
+     "↳ visemes" lane guarded by stage.visemeTargets(id).length > 0.
+  Model (timeline.js, stagestub.js, timeline_test.mjs) committed ba29d0c;
+  tests cover morph lerp, rhubarb keys, audio mutators+undo. All green.
+VERIFIED (real server :8020, real assets): 🎵 picker listed + added
+  audio/test/tone.wav, buffer decoded (8s), green block drawn, Web Audio
+  scheduled/rescheduled/stopped (ctx running), viseme lane rendered
+  importRhubarb keys, setMorph fired while scrubbing. Contract match confirmed:
+  real stage.js ships setMorph(id,name,weight) + visemeTargets(id) (returns
+  Object.keys(visemes)) — my `.length>0` guard works against both.
+DECISIONS:
+  - Audio duration is a client draw concern (decode+cache in tlui), NOT stored
+    in the {path,start,gain} schema — server already knows durations at mux.
+  - importRhubarb = simple per-cue ramp (shape 1 at cue start → 0 at end);
+    hold/crossfade tuning deferred (ponytail marker in timeline.js) until it
+    looks wrong on a real blendshape character.
+  - Audio blocks can extend past scene.duration (tone.wav is 8s in a 6s scene)
+    — left as-is; the ruler just clips visually. Trim is a later nicety.
+BLOCKED/REQUESTS:
+  - **Ownership note for orchestrator**: my tlui.js M4-B changes (+146 lines)
+    were committed inside Lane A's `df4e06f [laneA] M4-A ...`, not a [laneB]
+    commit — Lane A's commit swept my then-uncommitted tlui.js working changes
+    along with their dock.js/stage.js. Code is intact + verified; only the
+    attribution is off. Heads-up that our git hygiene let a cross-lane file
+    ride in on another lane's commit; a `git add <own files>` (not `-A`) avoids
+    it. Nothing for me to fix.
+NEXT: M4-B complete. Open items if a session 5 lands: audio block trim/clip to
+  duration, viseme import UI button (currently importRhubarb is API-only; Lane
+  C has a /rhubarb endpoint — could wire a "lip-sync from audio" button that
+  POSTs the clip and feeds the result to importRhubarb). Holding for SYNC/next
+  orchestrator update.