# Lane E — Director & export (branch `lane/e-director`)

**Scope: phase-5 milestones M10 + M11 + M12** (beats/onsets, auto-director, cinematic export) — see [`20-phase5.md`](20-phase5.md).

- Owned files: `backend/festival4d/audio_features.py`, `backend/festival4d/director.py`,
  `backend/tests/test_audio_features.py`, `backend/tests/test_director.py`,
  `frontend/src/director.js`, `frontend/src/exportVideo.js`. Nothing else.
- Fill the stub bodies foundation2 left; signatures, routes, and CLI dispatch already exist.
- Contracts you consume (frozen): `beats.json` shape, camPath JSON (quat `[x,y,z,w]`, Three.js
  space — convert COLMAP poses via `geometry.colmap_to_threejs`, never inline),
  `transport.captureAudioStream()`.
- Build order M10 → M11 → M12: the director consumes beats; export consumes the director's path.
  Each milestone is independently mergeable — don't hold M10/M11 hostage to M12.
- Degradation: no beats → director skips beat-snapping; no poses → director returns a clear
  error body, never a crash; export with no path → button stays disabled.

**Done when:** M10–M12 acceptance passes (browser evidence for M11/M12 in your status file),
`pytest` ≥ 121 + your tests, merged to `main` with synthetic end-to-end intact.