What was wrong:
- CR-01 (recorder.ts): encodeAndSendBuffer captured no port identity before
awaiting Promise.all(blobToBase64). If the port disconnected mid-encode
and onDisconnect synchronously reconnected (re-assigning keepalivePort
to a fresh instance), the post-await null-check evaluated false and
the BUFFER was posted on the NEW port — but the SW's per-request
onMessage listener was still bound to the OLD port (captured at
getVideoBufferFromOffscreen line 110). Result: SW timed out after
2 s, SAVE_ARCHIVE produced an empty-segments zip, data-loss path
masquerading as a benign timeout.
- CR-02 (background/index.ts): SW's onConnect handler attached
ONLY onDisconnect — no permanent onMessage sink. PING traffic
had no listener when getVideoBufferFromOffscreen wasn't running
(the normal idle state of the port), and field reports note Chrome's
SW idle-timer reset behaves inconsistently when no listener is
attached. Risk: PINGs silently dropped, SW evicted ~30 s into
recording, port torn down, next SAVE_ARCHIVE fails entirely.
- CR-03 (background/index.ts): offscreenReady is a one-shot Promise
resolved on the FIRST OFFSCREEN_READY message. If the SW is evicted
while the offscreen document persists, the next SW lifetime creates
a fresh Promise and waits on it forever — the offscreen never
re-emits OFFSCREEN_READY. startVideoCapture() hangs at
`await offscreenReady` until Chrome restarts.
- WR-03 (recorder.ts): `baseTimestamp + idx` (Date.now() + idx) used
millisecond resolution + array offset. Two REQUEST_BUFFER calls
within the same millisecond would collide, breaking the sort-by-
timestamp contract in SW-side mergeVideoSegments.
- WR-09 (recorder.ts): encodeAndSendBuffer always appended the
unfinalized in-flight segment to the BUFFER. That segment lacks
the Matroska SegmentSize and Cues that MediaRecorder.stop()
writes — re-introducing the "File ended prematurely" symptom
documented in debug session webm-playback-freeze.
What changed:
- recorder.ts encodeAndSendBuffer:
- Capture `portAtRequest = keepalivePort` BEFORE the encode.
- After the await, refuse to post if `keepalivePort !== portAtRequest`
(port was replaced by reconnect). SW already times out cleanly
after BUFFER_FETCH_TIMEOUT_MS = 2 s; the next SAVE_ARCHIVE
re-issues REQUEST_BUFFER on the fresh port. Stale data
NEVER reaches a stranger port.
- Include the in-flight segment ONLY when finalized.length === 0
(preserve the SAVE-within-first-10-s UX trade-off documented at
the original comment) — otherwise drop the unfinalized tail.
- Replace `baseTimestamp + idx` with module-level monotonic
`++segmentSeq` counter (zero wall-clock dependency).
- Switch from Promise.all/map+filter to a sequential for-loop
because each iteration now mutates the shared `segmentSeq`;
Promise.all timing would interleave assignments. Throughput
impact negligible (3 segments × ~50 ms base64 each ≈ 150 ms
vs ~50 ms parallel — still well under the 2 s SW budget).
- background/index.ts onConnect:
- Install a permanent `port.onMessage.addListener` that
explicitly drains PING and silently drops unknown traffic.
Per-request BUFFER listener still wins because it's attached
LATER in the listener chain when getVideoBufferFromOffscreen
fires; this sink only catches the idle PING stream and
guarantees the SW idle-timer reset is consumed by a real
handler.
- background/index.ts initialize():
- When `chrome.offscreen.hasDocument()` returns true on SW init,
immediately resolve `offscreenReady` AND null
`offscreenReadyResolve`. The offscreen MUST have completed its
bootstrap before it was observable via hasDocument(); waiting
for an OFFSCREEN_READY that will never come is a deadlock.
Why these fixes vs alternatives:
- CR-01: alternatives considered: (a) cancel encoding when port
disconnects (requires AbortController plumbing into blobToBase64);
(b) re-route the BUFFER through the new port via a per-port
request-id correlation. Both add machinery for a case the SW
already handles correctly (2 s timeout → retry). The capture-
identity check is the minimum-mechanism fix and matches REVIEW.md
CR-01 fix guidance exactly.
- CR-02: alternative considered: documenting "rely on kernel-level
port-message side effect for idle-timer reset" — REJECTED, this
is what the existing comment did and the field evidence shows
it's unreliable. Explicit listener is the safe default.
- CR-03: alternative considered: (a) have offscreen re-emit
OFFSCREEN_READY on every inbound SW message — adds noise to
the message bus and races with the original-bootstrap-emit.
Option (b) (resolve-on-hasDocument-true) is simpler, narrower,
and was explicitly recommended by REVIEW.md.
- WR-03: alternative considered: keeping Date.now() and adding a
microsecond-resolution offset via performance.now() — fragile
across SW respawns where performance.now() resets. Module-level
monotonic counter has zero wall-clock dependency.
- WR-09: alternative considered: forcing a synchronous rotation
at REQUEST_BUFFER time. Rejected — adds ~50–200 ms latency to
every save AND races with scheduleRotation()'s timer. The
"exclude unless empty" trade-off matches REVIEW.md option (a)
exactly and preserves the documented first-10-s UX path.
Validation evidence:
- npx tsc --noEmit: exit 0 (no type errors).
- npx vitest run --reporter=dot: 30/30 tests pass in 2.67 s
(8 test files, including port.test.ts which pins the reconnect
invariant and port-serialization.test.ts which pins the wire format).
- grep "as any\|@ts-ignore" src/offscreen/ src/background/index.ts
src/shared/: no matches (type-safety gate stays clean).
Pure rename pass — zero behavioural change at any call site. The
prior "chunk" naming is a vestige of D-09..D-11's chunk-level
buffer; under D-13 the unit of transfer is a self-contained ~10 s
WebM segment, so the type name now matches the data shape.
Renames propagated atomically:
- src/shared/types.ts
* TransferredVideoChunk → TransferredVideoSegment
(also: the `isFirst?: boolean` field is dropped — D-13 segments
are all implicitly their own header, so the flag is meaningless
and only existed for the retired ring-buffer's pin semantics)
* VideoChunk → VideoSegment (drops `isFirst?` for the same reason)
* PortMessage.chunks? → PortMessage.segments?
* VideoBufferResponse.chunks → VideoBufferResponse.segments
- src/offscreen/recorder.ts
* import type rename
* encodeAndSendBuffer's per-element accumulator + filter type
* the port.postMessage payload field
- src/background/index.ts
* import type rename
* getVideoBufferFromOffscreen reads `(msg as {segments?}).segments`
(matching the new wire field name)
* empty-buffer returns `{ segments: [] }`
* mergeVideoSegments signature takes VideoSegment[]
* createArchive consumes videoBufferResponse.segments
* saveArchive log line says "segments"
Verification:
- npx tsc --noEmit clean.
- npx vitest run → 28 passed / 2 failed (the 2 fixture-empirical
ffmpeg dry-runs; unchanged — they're gated on ./smoke.sh regen).
- npm run build succeeds, all 60 modules transformed.
- grep predicates clean in src/:
* no addChunk / trimAged / firstChunkSaved / isFirst
* no TransferredVideoChunk / VideoChunk (old names)
* 21 occurrences of new names propagated correctly
- Pre-existing port-serialization.test.ts still GREEN: its `isFirst`
references are inside inline-test-scoped objects (not imports
from production types), and its tests assert JSON-roundtrip
behaviour rather than the production type shape.
Follow-up to the D-13 activation in src/offscreen/recorder.ts. Each
entry on the BUFFER port message is now a self-contained WebM
segment (not a partial chunk), so the SW-side concat is trivial:
sort by timestamp and Blob-concatenate. The resulting multi-EBML-
header file plays natively in Chrome (SPEC §10 #7 scope).
Changes in src/background/index.ts:
- mergeVideoChunks renamed to mergeVideoSegments; doc comment and
log lines say "segment" throughout. No behavioural change beyond
removing the now-stale per-chunk `isFirst` logging.
- getVideoBufferFromOffscreen no longer reads or carries the
`isFirst` field when decoding wire payload into VideoChunk —
D-13's segment lifecycle makes the flag meaningless (every
segment is a fresh recorder boundary, every segment's first
chunk is implicitly the header). The field stays optional on
VideoChunk for one more commit; commit 4 sweeps the type
rename and drops it.
- The single mergeVideoChunks call site in createArchive updated
to the new name.
Verification:
- npx vitest run → 28 passed / 2 failed (same 2 empirical-ffmpeg
REDs from webm-playback.test.ts; unchanged from prior commit —
the fixture is still the stale single-continuous-recorder one).
- npx tsc --noEmit clean.
- src/background/index.ts now has zero references to addChunk /
trimAged / firstChunkSaved / isFirst.
- Read incoming port.chunks as TransferredVideoChunk[] (was
VideoChunk[] — but that was a lie because Blob doesn't survive
JSON serialization across the port boundary).
- Decode each wire chunk via base64ToBlob(wire.data, wire.type) and
resolve VideoBufferResponse with the resulting VideoChunk[]. The
existing mergeVideoChunks downstream sees real Blobs and produces
a real WebM-prefixed merged blob.
- Defensive per-chunk decode: log + skip individual decode failures
rather than blowing up the whole fetch. Falls back to
video/webm;codecs=vp9 if the wire chunk somehow omits the type
(defense-in-depth — the offscreen always populates it).
- Document the 2 s BUFFER_FETCH_TIMEOUT_MS budget: covers worst-case
encode + post-message + JSON parse with > 1.5 s of headroom for
the current 15-chunk × 100 KB sizing.
Refs: debug session d12-blob-port-transfer-fails, D-17 port lifecycle.
After collapsing vite.config.ts to use rollupOptions.input.offscreen =
'src/offscreen/index.html', crxjs preserves the 'src/' prefix in the
bundled output (Outcome A per RESEARCH.md Pitfall 5 dichotomy):
dist/src/offscreen/index.html (NOT dist/offscreen/index.html)
The pre-amendment leftover string 'offscreen/index.html' at
src/background/index.ts:45 would have produced
ERR_FILE_NOT_FOUND in chrome.offscreen.createDocument and broken
Plan 07's manual smoke load. Updated to match the actual emit path.
- npm run build exits 0; 7 dist/assets/*.js bundles produced
- dist/manifest.json permissions: desktopCapture present, tabCapture absent
- tsc --noEmit clean; 9/9 vitest tests still green
- ensureOffscreen URL string now matches dist/src/offscreen/index.html
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Plan 05 Task 2 — make the SW a pure coordinator that talks to the offscreen
via the long-lived 'video-keepalive' port (D-17, RESEARCH.md Pattern 5).
Additions:
- chrome.runtime.onConnect.addListener handler scoped to port name
'video-keepalive' + T-1-04 mitigation (port.sender?.id check). Stores port
in module-level videoPort: chrome.runtime.Port | null.
- getVideoBufferFromOffscreen(): port-based REQUEST_BUFFER round-trip with
a 2s timeout fallback to { chunks: [] }. Replaces the synchronous SW-local
getVideoBuffer() stub from Task 1.
- offscreenReady Promise + OFFSCREEN_READY onMessage case (RESEARCH.md
Pattern 4): startVideoCapture awaits this before sending START_RECORDING,
closing the 'Receiving end does not exist' race window (audit P1 #12).
- onMessage GET_VIDEO_BUFFER + SAVE_ARCHIVE rewritten to fetch the buffer
via the port instead of the deleted local array.
- onMessage sender.id !== chrome.runtime.id guard at handler top
(T-1-NEW-05-01 mitigation).
- chrome.runtime.onInstalled now calls indexedDB.deleteDatabase('VideoRecorderDB')
once to clean up the orphaned database from pre-Phase-01 builds
(T-1-NEW-05-02 / RESEARCH.md Runtime State Inventory).
Rule 2 deviation (orchestrator-flagged robustness):
- initialize() now calls chrome.offscreen.hasDocument() to detect existing
offscreen documents across SW respawns and update offscreenCreated
accordingly (audit P1 #8). Guarded with a typeof check to stay safe under
partial chrome stubs.
Verified: npx tsc --noEmit clean; npx vitest run 9/9 green (Plan 04
offscreen-side tests stay un-touched); no as any / @ts-ignore.
Plan 05 Task 1 — finish the SW shrink:
- DELETE videoBuffer: VideoChunk[] module state (buffer lives in offscreen per D-16)
- DELETE setupKeepalive + chrome.alarms registration (D-18; alarms never reset SW idle timer — port does)
- DELETE chrome.tabCapture.getMediaStreamId call (D-01: getDisplayMedia now runs inside offscreen)
- DELETE chrome.permissions.contains/request for tabCapture (broken — desktopCapture is the new manifest entry, but getDisplayMedia needs no runtime perm)
- DELETE comment-only references to removed symbols (so grep gates pass)
- REPLACE 'USER_MEDIA' as any → chrome.offscreen.Reason.DISPLAY_MEDIA (D-02; @types/chrome 0.0.268 exposes it)
- REPLACE justification copy to match RESEARCH.md Example C
- FIX (error as any) → instanceof Error pattern (CLAUDE.md rule)
- FIX chrome.tabs.sendMessage cast: explicit response type instead of 'as any'
- COLLAPSE REQUEST_PERMISSIONS handler: under getDisplayMedia, no runtime perm check is meaningful — just call startVideoCapture() (Rule 1 deviation; old code returned granted=false because tabCapture is no longer in manifest)
- Temporary stub: getVideoBuffer() returns { chunks: [] } — Task 2 deletes this and wires the port-based getVideoBufferFromOffscreen()
Verified: npx tsc --noEmit clean, npx vitest run 9/9 green, no as any / @ts-ignore.
- Add PortMessageType and PortMessage interface to src/shared/types.ts
for the long-lived port (offscreen ↔ SW; D-17 / Plan 04 wires the
ping loop + REQUEST_BUFFER / BUFFER traffic).
- Remove 'VIDEO_CHUNK' and 'VIDEO_CHUNK_SAVED' from MessageType union
(per D-19 — chunks no longer travel via chrome.runtime.sendMessage;
the IndexedDB SW-side plumbing is the audit P0 #2 broken path).
- OffscreenLogger class was already added alongside Task 2 because
recorder.ts imports it at module top.
Inline SW cleanup (Rule 3 — blocking dependency, plan acceptance gates
on `npx tsc --noEmit` exit 0):
- Remove src/background/index.ts VIDEO_CHUNK + VIDEO_CHUNK_SAVED case
branches (refs to deleted union members).
- Remove now-unreferenced loadChunkFromIndexedDB / openIndexedDB
(only reachable from the deleted VIDEO_CHUNK_SAVED branch).
- Remove now-unreferenced addVideoChunkFromBlob / cleanupVideoBuffer
/ firstChunkSaved / VIDEO_BUFFER_DURATION_MS constant (the SW-side
ring buffer now lives in src/offscreen/recorder.ts per D-16).
- Keep SW-side `videoBuffer: VideoChunk[] = []` as a placeholder; Plan
04 wires it to fetch from offscreen over the keepalive port. The
remaining `getVideoBuffer` + `saveArchive` callers continue to
compile against the empty array until Plan 04 lands.
- Plan 05 owns the broader SW shell cleanup.
Verification (post-commit):
- npx vitest run tests/offscreen/ring-buffer.test.ts tests/offscreen/codec-check.test.ts → 6/6 PASS
- npx tsc --noEmit → exit 0
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
