[laneC] log: M2/M3 render pipeline done

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

logs/laneC.md

@@ -35,3 +35,32 @@ BLOCKED/REQUESTS: none.
 NEXT: M2 (when unlocked): scene-validation hardening + asset thumbnails
 endpoint. M3 render pipeline (ffmpeg encode + web/render.js) is designed in
 C-server.md §C5, endpoints already stubbed — implement at SYNC-2/M3.
+
+## 2026-07-18 session 2
+DONE: M2 thumbnails + M3 render pipeline (orchestrator green-lit both). Commit b627a0f.
+- `/render/begin` (uuid dir + meta.json, 503 if no ffmpeg), `/frame/{n}`
+  (PNG->frames/{n:06d}.png, 400 on empty), `/end` (spawns bg ffmpeg thread:
+  libx264 crf18 yuv420p, 400 if no frames), `/status` (queued|encoding|
+  done|error+log tail; on-disk out.mp4 fallback after restart), `/out.mp4`.
+- Boot-time `reap_renders()` deletes render dirs >48h.
+- `/assets/thumb?path=` serves same-stem image sidecar (404 if none).
+- `web/render.js`: draftRecord (MediaRecorder webm), finalRender
+  (timeline.step -> renderActiveCamera -> toBlob -> POST, <=4 in flight,
+  resize+restore renderer), download() helper. node --check clean.
+- `test_server.py`: added render group (ffmpeg lavfi -> 30 PNGs -> begin ->
+  post -> end -> poll -> ffprobe duration ~1s) + thumbnail asserts.
+  `OK: 6 test groups passed`.
+DECISIONS:
+- Render state in-memory (single-process local tool); status() infers from
+  disk after a restart. ponytail-commented.
+- Thumbnails pass-through, no resize — Pillow would be a new dep (stack rule
+  says log a REQUEST first); not worth it until dock load is measurably slow.
+- finalRender total frames = round(duration*fps); relies on timeline.step
+  being deterministic (orchestrator verified).
+BLOCKED/REQUESTS:
+- finalRender's per-frame path depends on Lane A `stage.renderActiveCamera`
+  as a real render target (their M2). Server + ffmpeg path fully tested with
+  synthetic frames; the browser client path is unexercised until A lands it.
+NEXT: M4 is locked. When unlocked: ffmpeg audio mux (scene audio[]),
+/mb/submit MODELBEAST proxy, scripts/graft_limb.py. Meanwhile available to
+integration-test finalRender once Lane A's renderActiveCamera lands.