Per debug session webm-playback-freeze "Activation Plan" step 4: the
D-09..D-11 ring-buffer semantics (first-chunk header pin + 30 s age trim)
are being replaced by D-13 restart-segments. The pinned-header assertions
were architecture-specific and become meaningless once each segment is
a self-contained WebM with its own EBML header and seed keyframe.
Changes:
- tests/offscreen/ring-buffer.test.ts: collapsed to a single breadcrumb
test pointing at the successor file. Kept the path so git history /
failure bisects land on the retirement commit cleanly.
- tests/offscreen/segment-rotation.test.ts (new): 8 tests pinning the
D-13 invariants against the production recorder module:
* MAX_SEGMENTS = 3, SEGMENT_DURATION_MS = 10_000 (= legacy 30 s window)
* empty-by-default, ordered, oldest-evicted-at-cap
* resetBuffer clears
* getSegments returns a defensive snapshot (no internal aliasing)
Uses a `pushSegmentForTest` seam so vitest can drive rotation
deterministically without instantiating a real MediaRecorder.
RED today by design (TDD discipline) — the segment-rotation suite
imports `getSegments`, `pushSegmentForTest`, `MAX_SEGMENTS`,
`SEGMENT_DURATION_MS` from src/offscreen/recorder.ts. Those exports
land in the next commit. tsconfig.include is "src" only so tsc stays
clean during the RED window.
