revert(01): reopen Phase 1 — D-13 multi-EBML-concat is unplayable

REQ-video-ring-buffer flipped from [x] back to [ ]. ROADMAP.md Phase 1
row reverted from [x] Closed 2026-05-15 to [ ] reopened 2026-05-16.
STATE.md status flipped phase_complete → phase_reopened with full
historical narrative preserved.

Root cause (confirmed at byte level by gsd-debugger 2026-05-16):
D-13's concat-of-self-contained-WebM-segments architecture produces a
3-EBML-header WebM that standards-compliant Matroska parsers
(mpv, ffmpeg, Chrome HTMLMediaElement) play only as the first segment
(~9.94 s) and silently drop the remaining 2 segments. Confirmed via
operator mpv drag-drop test of BOTH the canonical 2026-05-15 closure
fixture and the 2026-05-16 UAT-produced fixture — both exhibit the
same broken playback.

The 2026-05-15 "operator-confirmed clean Chrome playback" assessment
was insufficient: it verified the file plays without freezing but did
not measure total duration. Phase 1's primary deliverable
(REQ-video-ring-buffer / SPEC §10 #7) is therefore NOT satisfied.

Fix path chosen by user: ts-ebml (parse) + webm-muxer (write) to
replace mergeVideoSegments file-concat with real single-EBML remux.
Will land as Plan 01-08 via fresh /gsd-plan-phase ceremony.

RED test landed in tests/offscreen/webm-playback.test.ts (2 new
assertions on container-format-duration + ffmpeg-full-decode-duration).
2 failures, 53 baseline tests still GREEN.

Option C port-lifecycle refactor (debug session
empty-archive-port-race, commits 674c415..f0871c0) DID land cleanly
and is retained — that fix was orthogonal and correctly resolved the
silent-empty-archive symptom that previously masked this deeper bug.

Debug session: .planning/debug/d13-multi-ebml-concat-unplayable.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -22,7 +22,7 @@ working export → green §10 smoke → harden + clean up**.
 
 Decimal phases appear between their surrounding integers in numeric order.
 
-- [x] **Phase 1: Stabilize video pipeline** — Collapse offscreen duality, fix MediaRecorder shadow, fix WebM ring buffer playability, replace `chrome.tabCapture` with offscreen `getDisplayMedia` (AMENDED from original DEC-003). **Closed 2026-05-15** — D-12 ffprobe gate + A3 empirical-playback gate both green against `tests/fixtures/last_30sec.webm` (1.6 MB VP9 1142×1038); D-13 restart-segments retired D-09..D-11 mid-phase; 30/30 vitest green, tsc clean. SPEC §10 #2, #3, #7 functionally satisfied (end-to-end Phase 4 smoke remains owner of §10).
+- [ ] **Phase 1: Stabilize video pipeline** — Collapse offscreen duality, fix MediaRecorder shadow, fix WebM ring buffer playability, replace `chrome.tabCapture` with offscreen `getDisplayMedia` (AMENDED from original DEC-003). **Closed 2026-05-15 then REOPENED 2026-05-16**: the 2026-05-15 closure was based on insufficient operator playback verification; D-13's concat-of-self-contained-segments architecture produces a multi-EBML WebM that plays only ~9 s instead of ~30 s in standards-compliant parsers (mpv, ffmpeg, Chrome HTMLMediaElement). UAT Test 3 retest on 2026-05-16 confirmed via byte-level EBML probe. SPEC §10 #7 not actually satisfied. Plan 01-08 (WebM remux via ts-ebml + webm-muxer) replaces `mergeVideoSegments`'s file-concat with a real single-EBML remux. See `.planning/debug/d13-multi-ebml-concat-unplayable.md`. Option C port-lifecycle refactor (debug session `empty-archive-port-race`) DID land cleanly and is retained. Phase 1 will additionally absorb whole-desktop + auto-start UX work (Plans 01-09/01-10) per the 2026-05-16 amended charter.
 - [ ] **Phase 2: Stabilize DOM + event capture privacy** — Migrate rrweb to v2 `maskInputFn`, plug `content/index.ts setupInputLogging` password leak
 - [ ] **Phase 3: Stabilize export pipeline** — Restore user-activation gesture in popup, delete dead `permissions.request`, replace base64 `data:` URL with Blob URL minted in offscreen
 - [ ] **Phase 4: SPEC §10 smoke verification** — End-to-end install-and-record-and-export pass against all 9 acceptance criteria