Four RED tests pin D-10 (header pinning) and D-11 (30s trim) contracts:
- 'first chunk is header' — isFirst marker on first addChunk
- 'second chunk is NOT header' — only the first is pinned
- 'trim 30s — keeps header, evicts aged tail' — header survives indefinitely
- 'trim with empty buffer does not throw' — defensive edge case
Plan 03 must export {addChunk, trimAged, getBuffer, resetBuffer} from
src/offscreen/recorder.ts to flip these to GREEN.
Also stages tests/fixtures/.gitkeep so the fixture dir survives clean
checkouts (Plan 07 drops a known-good last_30sec.webm into it after the
manual smoke test).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
