[laneB] log: M2 session 3

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

logs/laneB.md

@@ -103,3 +103,34 @@ BLOCKED/REQUESTS:
 NEXT: Hold at M2. Remaining M2 polish if a session 3 is granted: undo already
   wired to Ctrl+Z; could add snapping increment config + keyable-param add UI
   (currently params keys come from Lane A capture/inspector). Await SYNC 2.
+
+## 2026-07-18 session 3 (M2 polish)
+DONE: All three orchestrator session-3 items.
+  1. Absorbed `_mirror` (orchestrator's seam) — reviewed; it upserts dock-added
+     stage entities into `scene.entities` with empty tracks and drops them when
+     `stage.getEntity(id)===null`. Fixed the STUB to make removal testable:
+     `removeEntity` now fires `onChange` WITH the removed entity object (was
+     firing `null`, so `_mirror(null)` early-returned and never removed).
+     Added timeline_test.mjs lifecycle case: dock-add → keyframe → remove,
+     asserting entity+empty-tracks appear then vanish.
+  2. `setDuration(x)` mutator: clamps the playhead into range, KEEPS keys past
+     the new end (lossless), notifies the UI (reuses onLoad → syncRows +
+     refreshBar). Wired the dur field to it — plain `scene.duration = x` skipped
+     the bar refresh. Test asserts clamp + key retention + notify.
+  3. Snap-increment select (frame / 0.1 / 0.25 / 1s) in the scene bar; `_snap`
+     rounds to the chosen step (Alt still = free). Keyable-param add: dblclick a
+     params lane captures the entity's current param values as keys (skips
+     `type`/boolean descriptors) — mirrors the transform-capture dblclick.
+DECISIONS:
+  - params lane now shows only when the entity has ≥1 param key OR kind is
+    camera/light. `_mirror` seeds `tracks.params=[]` (truthy), which was
+    giving every mirrored character an empty params lane; tightened to
+    `tracks?.params?.length > 0 || camera|light`.
+  - setDuration reuses the onLoad callback list as its "refresh UI chrome" hook
+    rather than adding a second callback channel (lazy; onLoad handler already
+    does syncRows+refreshBar+draw).
+BLOCKED/REQUESTS: none. Verified with a throwaway harness (`_check.html`,
+  served :8099, deleted, NOT committed). timeline_test.mjs green.
+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.