diff --git a/logs/laneC.md b/logs/laneC.md
index 2dd5601..2927530 100644
--- a/logs/laneC.md
+++ b/logs/laneC.md
@@ -64,3 +64,37 @@ BLOCKED/REQUESTS:
 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.
+
+## 2026-07-18 session 3
+DONE: M4 complete (unlocked after SYNC 3). Commit be65355.
+- Audio mux: `/render/end` now accepts `{audio:[{path,start,gain}]}`, muxes via
+  ffmpeg adelay+volume+amix -> aac -shortest; audio paths path-guarded (400 on
+  missing). `render.js finalRender` passes `opts.audio` through.
+- `scripts/graft_limb.py`: headless Blender (`blender -b -P ... -- --body B
+  --limb L --bone NAME --out O`). Align limb root head->target bone world head,
+  join armatures, parent limb root under target (keep offset), join meshes
+  (vgroup weights survive). Refusal: overlapping bones -> GraftRefused ->
+  exit 2 "re-skin, don't graft". No finish/decimate. `--selftest` builds
+  synthetic body/limb GLBs and verifies refusal + graft paths under Blender.
+- `/mb/submit`: MODELBEAST proxy, SCENEGOD_MB=1 gated (503 otherwise), token
+  from ~/Documents/backnforth/.env at request time (never logged; errors
+  scrub it), /api/assets multipart -> /api/jobs, mirrors meshgod/ops.py.
+- `test_server.py`: 8 groups green (added audio-stream assert, MB gating,
+  MB two-step contract via in-process mock — no farm jobs).
+DECISIONS:
+- Blender 5 glTF importer injects a stray unparented 42-vert icosphere on
+  every import; `_import` now keeps only rig-connected meshes (parented to
+  armature / has vgroups / armature modifier) and deletes strays. Right filter
+  for a graft tool regardless.
+- graft refusal check: provides = limb bones - {limb root}; refuse if
+  provides ∩ body bones. Attach/root bone sharing the target name is expected.
+- MB test uses a stdlib http.server mock + a 2nd scenegod instance; asserts
+  Bearer token forwarded, multipart upload, asset_id chained into job payload.
+BLOCKED/REQUESTS: none.
+BACKLOG (from orchestrator, not urgent): draft webm via MediaRecorder is
+untested in the embedded preview (rAF suspension). Needs one verification in a
+real Chrome window before calling draftRecord done — client-only, needs Lane A
+stage running live; deferred.
+NEXT: Lane C M1-M4 all shipped. Available for polish / integration support.
+Blender binary here is /Applications/Blender.app/Contents/MacOS/Blender (not
+on PATH as `blender` in this session, contrary to orchestrator note).