# Status — lane-C

## Round 1 — 2026-07-16 — STATUS: ready_to_merge

**Directives acknowledged:** round 0 of plan/DIRECTIVES.md (run order C→A→D→B; C starts first
as the longest lane + earliest API-contract validation; merge when acceptance passes; maintain
this file; evidence discipline). No new rounds present on origin at time of writing.

**Acceptance checklist (lane brief M4/M5/M6 + timeline markers) — all pass:**
- [x] **M4 synchronized playback.** Master clock from `performance.now()` (never a `<video>`).
      Timebase mapping proven exact by seek: at t_global=8.0 → cam0=8.000, cam1=6.630,
      cam2=8.842 s, err=0 ms each. Per-video correction = hard-seek >150 ms / nudge
      playbackRate ±5% 20–150 ms / lock <20 ms, driven by `requestVideoFrameCallback`
      (exact `mediaTime`) with a currentTime+½-frame fallback when rVFC is unavailable/stale.
      Out-of-range videos pause+dim (cam1 at t=0, target −1.37 s). One audio source; dev
      overlay shows per-video sync ms. Measured continuous-playback **inter-video desync =
      13 ms mean / 46 ms max** over 6 s (< 50 ms), driven by a setTimeout pump (see env note).
- [x] **M5 3D viewer.** PLY point cloud (3106 pts, vertex colors); per-video camera-path lines
      + current-pose frusta (colored); OrbitControls; snap-to-camera tweens viewer to the pose
      (following cam1: camPos≈(1.78,2.63,9.25)≈true center (0,2.4,9.4); fov=36°≈2·atan(H/2fy);
      orbit disabled) and free-roam restores (fov→50°, orbit on). All COLMAP→Three via frozen
      `lib/pose.js` — never reimplemented.
- [x] **M6 anchor overlays.** Per-video letterbox-correct transparent canvas; anchors projected
      via pose.js camera. Overlay projection agrees with an independent direct COLMAP pinhole to
      **1.45e-13 px** across 3 cams × 3 times × 4 anchors; corners match a standalone Python
      pinhole. Behind-camera cull (z_cam<0). Stage corners render/track on all in-range videos.
- [x] **Timeline event markers.** 7 events → colored markers + legend; hover→description
      tooltip; click→jump (pyro marker → t_global 10.00). Scrubber seeks/parks all videos.
- [x] **No console errors** across load/play/seek/snap/timeline; production build clean
      (`npm run build`, 16 modules).

**Env note (not a blocker):** the automated browser pane reports `document.hidden=true`, so rAF
and rVFC only fire during screenshots — continuous playback can't be observed by polling here.
Verified deterministically instead (seek exactness to 0 ms; projection to 1e-13 px; a
setTimeout-driven run of the real correction code → 13 ms mean inter-video desync). A real
focused browser runs the rAF loop at 60 fps and rVFC drives even tighter absolute sync.

**Owned-files discipline:** committed only `frontend/**` + this status file. Left untouched the
other lanes' in-tree changes (A: audio_sync/ingest; B: frames/geometry/sfm; D: events_ai).
Added `frontend/src/lib/timebase.js` + `poseTrack.js` (new files inside lane C's ownership).
No frozen files edited; no new deps (three was already present); **no change requests.**

**Repo note for coordinator:** this working directory is shared/contended — `lane/c-viewer`
was reset to foundation (5fa7301) and HEAD moved to `lane/d-events` between my session-start
commit and now, and `main` has since advanced to lane D's self-merge (6ec55c7). I re-committed
lane C's frontend cleanly on `lane/c-viewer` off the foundation base (commit cd88204, 1 ahead /
3 behind main). lane C→main is **conflict-free** (frontend/** is disjoint from the backend
changes lanes A/B/D put in main) but is a merge, not a fast-forward. I did **not** self-merge
because the required `git checkout main` in this shared tree would collide with other lanes'
**uncommitted** backend changes living here — that's for a clean clone/worktree to do.

**Next:** coordinator to merge `lane/c-viewer` (cd88204) → `main` from a clean tree (frontend-
only, conflict-free). Phase-3 seams left as clean stubs: `annotate.js` (M8), `camPath.js` (M9).