mokosh/.planning/phases/04-harden-clean-up-optional/04-08-PLAN.md

phase, slug, plan, type, wave, depends_on, files_modified, autonomous, requirements, tags, user_setup, must_haves

phase	slug	plan	type	wave	depends_on	files_modified	autonomous	requirements	tags	user_setup	must_haves
04	harden-clean-up-optional	08	auto	5.5	01 02 03 04 05 06	tests/uat/fixtures/synthetic-display-source.webm src/test-hooks/offscreen-hooks.ts globals.d.ts manifest.json vite.config.ts vite.test.config.ts tests/uat/extension-page-harness.ts tests/uat/lib/harness-page-driver.ts tests/uat/harness.test.ts tests/uat/spike-a33-sw-persistence.ts	true		uat-harness a33 methodology-reframe video-file-source htmlvideoelement-capturestream canvas-throttling-fix chrome-bug-653548 charter-d-p4-01 roadmap-sc-1-closes post-debug-session-2		truths artifacts key_links installFakeDisplayMedia() at src/test-hooks/offscreen-hooks.ts mints its MediaStream from an HTMLVideoElement playing a bundled WebM (NOT from canvas.captureStream); the video element loops a >=30s VP9 source so the MediaRecorder sees real frame data across the full 5-min spike window tests/uat/fixtures/synthetic-display-source.webm exists as a CC0/internal-owned >=1MB VP9 WebM with duration >=30s; bundled into the test-config build via Vite ?url import (per Plan 01-10 mokosh-mark.svg precedent) tests/uat/spike-a33-sw-persistence.ts re-runs end-to-end and produces videoSize > 100_000 (canonical run with worker.close()) — empirically refutes the previous 8505-byte 0-frames methodology failure and confirms ROADMAP SC #1 architectural integrity per debug session-2 verdict assertA33 / driveA33 / orchestrator wiring land per the original Plan 04-04 Pattern 4 verbatim (cs-injection-world precedent NOT applicable — A33 is host-side CDP-driven, not page-side rrweb-driven) stopServiceWorker(browser, extensionId) helper at tests/uat/lib/harness-page-driver.ts is reused verbatim from Plan 04-04 (already committed at 3726eee); no new helper symbol needed A33 env-gated by SKIP_LONG_UAT (default RUN for closure + alpha gate; SKIP_LONG_UAT=1 to skip per-commit iteration); 95s baseline preserved when skipped UAT harness count flips 33 -> 34 (A33 added); 34/34 GREEN when SKIP_LONG_UAT unset; vitest 183/183 GREEN preserved ROADMAP SC #1 (SW state persistence) GREEN — A33 empirical evidence that a 5-min idle + Puppeteer worker.close() + SAVE_ARCHIVE produces video/last_30sec.webm with size > 100 KB Tier-1 FORBIDDEN_HOOK_STRINGS inventory unchanged at 12 entries (lockstep across tests/uat/harness.test.ts + tests/background/no-test-hooks-in-prod-bundle.test.ts) — Plan 04-08 introduces NO new __MOKOSH_UAT__-gated symbols on production bundle; the bundled WebM ships only in test build per Vite ?url + test-config gating Pre-checkpoint bundle gates 6/6 PASS unchanged from Plan 04-03 baseline (new Function=0 + eval=0 + Buffer.=1 pre-existing JSZip + window./document.=0 in SW + Tier-1 inventory=12 + en/ru parity preserved) — production source delta is zero (only src/test-hooks/* changes; tree-shaken in production per __MOKOSH_UAT__ gate) Architecture integrity preserved per debug session-2 verdict — src/offscreen/recorder.ts:91 `let segments: Blob[] = []` RAM-only architecture is canonically correct; no IndexedDB persistence work, no chrome.storage migration, no offscreen-document lifecycle changes path provides min_size_bytes tests/uat/fixtures/synthetic-display-source.webm Bundled CC0/internal VP9 WebM source for HTMLVideoElement.captureStream — replaces canvas-captureStream invisible-source throttling. Size 1-3 MB; duration >=30s; loopable (autoplay+loop+muted). License: internal capture by this project's MediaRecorder pipeline (CC0-equivalent project-owned) 1000000 path provides contains src/test-hooks/offscreen-hooks.ts installFakeDisplayMedia() rewritten to mint MediaStream from HTMLVideoElement.captureStream(30); displaySurface monkey-patch preserved; lifecycle (idempotent install + idempotent uninstall) preserved; A23 constraints capture preserved; all 6 existing bridge ops (install-fake-display-media + dispatch-ended + has-stream + get-display-surface + get-segment-count + get-last-getDisplayMedia-constraints) preserved videoEl.captureStream path provides contains globals.d.ts Ambient declaration for `*.webm?url` Vite asset import (mirrors existing `*.svg?url` block at lines 34-37) webm?url path provides contains tests/uat/extension-page-harness.ts assertA33 page-side method registered on __mokoshHarness OR existing assertA2 reused for prime step (decided by read_first; Plan 04-04 REVISION iter-2 Option B precedent prefers reuse) assertA33 path provides contains tests/uat/lib/harness-page-driver.ts driveA33(page, browser, extensionId, downloadsDir) host-side driver implementing the 5-min idle + stopServiceWorker + SAVE_ARCHIVE + JSZip video-size check (Plan 04-04 Pattern 4 verbatim; REVISION iter-2 Option B inline SAVE_ARCHIVE dispatch) driveA33 path provides contains tests/uat/harness.test.ts driveA33 import + driveA33Wrapped wrapped-driver const + drivers-array push entry with SKIP_LONG_UAT env-gate (per Plan 04-04 Wave 1 spec verbatim) driveA33Wrapped from to via pattern src/test-hooks/offscreen-hooks.ts installFakeDisplayMedia tests/uat/fixtures/synthetic-display-source.webm via Vite ?url import import videoUrl from '../../tests/uat/fixtures/synthetic-display-source.webm?url' OR equivalent gated import synthetic-display-source.webm?url from to via pattern src/test-hooks/offscreen-hooks.ts mintStream() HTMLVideoElement.captureStream(30) + displaySurface monkey-patch videoEl.captureStream(30); patchDisplaySurface(stream) videoEl.captureStream from to via pattern tests/uat/harness.test.ts driveA33Wrapped tests/uat/lib/harness-page-driver.ts driveA33(page, browser, extensionId, downloadsDir) (page) => driveA33(page, handles.browser, handles.extensionId, handles.downloadsDir) handles.browser.*handles.extensionId from to via pattern tests/uat/lib/harness-page-driver.ts driveA33 video-size check zip.file('video/last_30sec.webm') -> byteLength > 100_000 JSZip.loadAsync + entry.async('uint8array') video/last_30sec.webm

**Methodology reframe for ROADMAP SC #1.** Per debug session-2 (`.planning/debug/sw-offscreen-persistence-investigation-session-2.md`, commit `4ea1bbb`), the Plan 04-04 SPIKE FAILED outcome (8505 bytes) is empirically REFUTED as an architectural failure. Three independent probes converged on the canonical NO answer:

1. Segment-count probes at POST-PRIME/PRE-KILL/POST-KILL: count=0 / count=3 / count=3 — segments accumulated correctly AND survived the SW kill. The let segments: Blob[] = [] RAM-only architecture (src/offscreen/recorder.ts:91) is NOT broken.
2. Step C variant (SPIKE_SKIP_SW_KILL=1; no worker.close()): IDENTICAL 8505-byte failure — Puppeteer CDP worker.close() is NOT the cause.
3. Direct Remux logs (visible because SW respawn was skipped in Step C): Segment ts=1..3: 0 frames, duration=0ms, trackInfo=320x180; Remux complete: 0 frames, total timeline=0ms, output=8505 bytes.

Root cause: installFakeDisplayMedia() at src/test-hooks/offscreen-hooks.ts:139-264 mints a canvas.captureStream(30) from a hidden -9999px-offset 320x180 canvas. Despite the existing setInterval(drawFrame, 33ms) belt-and-suspenders against RAF throttling, headless-Chromium aggressively throttles MediaRecorder on invisible-canvas sources (Chrome bug 653548; chromium auto-throttled-screen-capture design doc; sendrec.eu "Why Canvas Breaks Your Screen Recorder"). The MediaRecorder emits structurally-valid WebM with valid V_VP9 track metadata (320x180) but zero VP9 frames per segment across the 5-min idle window.

Fix: Replace the canvas.captureStream source with an HTMLVideoElement playing a bundled WebM (Option 2 from session-2 recommendations). Video-file-backed videoEl.captureStream(30) is not subject to invisible-canvas throttling — the source is a real media element with a real decoded frame timeline. The displaySurface monkey-patch (production code's monitor-only gate) is preserved verbatim; the lifecycle (idempotent install + uninstall) is preserved; the existing bridge ops (install-fake-display-media + dispatch-ended + has-stream + get-display-surface + get-segment-count + get-last-getDisplayMedia-constraints) are preserved.

Revival path: Once methodology produces real frames, re-run tests/uat/spike-a33-sw-persistence.ts — it MUST exit 0 with videoSize > 100_000. Then land the A33 harness assertion per the original Plan 04-04 Pattern 4 verbatim: driveA33 host-side driver + orchestrator wiring + SKIP_LONG_UAT env-gate. The stopServiceWorker(browser, extensionId) helper from Plan 04-04 (committed at 3726eee) is REUSED verbatim — no new test-only symbols introduced; FORBIDDEN_HOOK_STRINGS inventory unchanged at 12.

Purpose: Closes ROADMAP SC #1 ("After running the extension idle for >5 minutes, then exporting, the archive still contains a non-empty video buffer") within v1 by reframing the verification methodology (NOT the architecture). Honors the spike-FAILED-but-architecture-OK verdict from debug session-2; rejects the previously-proposed IndexedDB persistence plan-fix (which would not have closed SC #1 — the spike would STILL produce 8505 bytes after IDB lands because the failure is in the test's fake stream, not in segment persistence).

Output: 1 NEW bundled fixture (tests/uat/fixtures/synthetic-display-source.webm); rewrite of installFakeDisplayMedia() (canvas -> HTMLVideoElement); 1 ambient module declaration for *.webm?url; 1 NEW harness assertion (A33; harness count 33->34); driveA33 + orchestrator wiring; spike script re-runs PASSED. ROADMAP SC #1 flips OPEN -> GREEN.

<execution_context> @$HOME/.claude/get-shit-done/workflows/execute-plan.md @$HOME/.claude/get-shit-done/templates/summary.md </execution_context>

@.planning/PROJECT.md @.planning/ROADMAP.md @.planning/STATE.md @.planning/phases/04-harden-clean-up-optional/04-CONTEXT.md @.planning/phases/04-harden-clean-up-optional/04-PATTERNS.md @.planning/phases/04-harden-clean-up-optional/04-04-PLAN.md @.planning/phases/04-harden-clean-up-optional/04-04-SUMMARY.md @.planning/debug/sw-offscreen-persistence-investigation-session-2.md

Source files — locus of the methodology reframe

@src/test-hooks/offscreen-hooks.ts @src/offscreen/recorder.ts @tests/uat/extension-page-harness.ts @tests/uat/lib/harness-page-driver.ts @tests/uat/harness.test.ts @tests/uat/lib/launch.ts @tests/uat/spike-a33-sw-persistence.ts

Vite ?url import precedent (Plan 01-10 mokosh-mark.svg pattern)

@src/welcome/welcome.ts @globals.d.ts @manifest.json @vite.config.ts @vite.test.config.ts

Prior plan SUMMARYs — direct ancestors

@.planning/phases/01-stabilize-video-pipeline/01-10-SUMMARY.md @.planning/phases/03-spec-10-smoke-verification-dom-event-log-verification/03-04-SUMMARY.md

From src/test-hooks/offscreen-hooks.ts:139-264 (CURRENT installFakeDisplayMedia — the methodology failure locus):

// CURRENT (broken under 5-min headless idle per debug session-2 verdict):
const canvas = document.createElement('canvas');
canvas.width = 320; canvas.height = 180;
canvas.style.position = 'fixed'; canvas.style.top = '-9999px'; canvas.style.left = '-9999px';
document.body.appendChild(canvas);
const ctx = canvas.getContext('2d');
// ... drawFrame loop + setInterval(drawFrame, 33) ...
const mintStream = (): MediaStream => {
  const stream = canvas.captureStream(30);  // <- THE THROTTLING SOURCE
  patchDisplaySurface(stream);
  return stream;
};

REPLACEMENT pattern (HTMLVideoElement.captureStream — Plan 04-08):

// Plan 04-08 methodology reframe — video-file-backed MediaStream.
// canvas.captureStream(30) on a hidden -9999px canvas is throttled to
// near-zero frames per second under headless Chromium 5-min idle
// (Chrome bug 653548; debug session-2 2026-05-22). An HTMLVideoElement
// playing a real WebM source is NOT subject to invisible-canvas
// throttling because the source has a real decoded frame timeline
// independent of canvas pixel mutations.
//
// References:
//   - debug session-2 verdict at .planning/debug/sw-offscreen-persistence-investigation-session-2.md
//   - HTMLVideoElement.captureStream:
//     https://developer.mozilla.org/docs/Web/API/HTMLMediaElement/captureStream
//   - Chrome bug 653548 (auto-throttled canvas captureStream):
//     https://bugs.chromium.org/p/chromium/issues/detail?id=653548

import sourceUrl from '../../tests/uat/fixtures/synthetic-display-source.webm?url';

const videoEl = document.createElement('video');
videoEl.src = sourceUrl;
videoEl.loop = true;       // loop indefinitely so 5-min idle has source frames
videoEl.muted = true;      // muted required for autoplay per Chrome policy
videoEl.autoplay = true;   // ensure playback starts without user gesture
videoEl.style.position = 'fixed';
videoEl.style.top = '-9999px';
videoEl.style.left = '-9999px';
document.body.appendChild(videoEl);

// Wait for the first frame to ensure captureStream returns live tracks
// (not stalled tracks awaiting first decode). Use 'canplay' event +
// explicit .play() for headless headless reliability.
await new Promise<void>((resolve, reject) => {
  videoEl.addEventListener('canplay', () => resolve(), { once: true });
  videoEl.addEventListener('error', () => reject(new Error('video load failed')), { once: true });
});
await videoEl.play();

const mintStream = (): MediaStream => {
  // captureStream(30) — request 30 fps; the actual cadence is driven
  // by the source video's frame timeline.
  const stream = (videoEl as HTMLVideoElement & {
    captureStream: (fps?: number) => MediaStream;
  }).captureStream(30);
  patchDisplaySurface(stream);  // preserve existing monkey-patch
  return stream;
};

From src/welcome/welcome.ts:46 (Plan 01-10 Vite ?url precedent — direct analog):

import markUrl from '../shared/brand/mokosh-mark.svg?url';

From globals.d.ts:34-37 (Plan 01-10 ambient module decl — direct analog to copy):

declare module '*.svg?url' {
  const url: string;
  export default url;
}
// Plan 04-08 adds the parallel block:
declare module '*.webm?url' {
  const url: string;
  export default url;
}

From src/test-hooks/offscreen-hooks.ts:271-291 (uninstallFakeDisplayMedia — preserve idempotent teardown):

// Existing teardown handles canvas removal + RAF cancel + interval clear.
// Plan 04-08 adapts: cancel video, removeChild(videoEl), null the refs.
// Idempotency contract unchanged.

From tests/uat/lib/harness-page-driver.ts:68-80 (stopServiceWorker helper — REUSED verbatim from Plan 04-04):

// Already committed at 3726eee; Plan 04-08 reuses without modification.
export async function stopServiceWorker(browser: Browser, extensionId: string): Promise<void> {
  const host = `chrome-extension://${extensionId}`;
  const target = await browser.waitForTarget(
    (t) => t.type() === 'service_worker' && t.url().startsWith(host),
  );
  const worker = await target.worker();
  if (worker !== null) {
    await worker.close();
  }
}

From Plan 04-04 PLAN.md Pattern 4 (driveA33 host-side body — REVIVED VERBATIM under valid methodology):

const A33_IDLE_WAIT_MS = 5 * 60 * 1000;
const A33_NEW_SW_BOOT_MS = 500;
const A33_OVERALL_TIMEOUT_MS = A33_IDLE_WAIT_MS + 60_000;
const A33_SAVE_ARCHIVE_TIMEOUT_MS = 15_000;
const A33_DOWNLOAD_SETTLE_MS = 5_000;
const A33_VIDEO_SIZE_FLOOR_BYTES = 100_000;

export async function driveA33(
  page: Page,
  browser: Browser,
  extensionId: string,
  downloadsDir: string,
): Promise<AssertionRecord> {
  const r: AssertionRecord = { name: 'A33', passed: false, checks: [], diagnostics: [] };

  // Step 1: prime via __mokoshHarness.assertA2 (canonical fresh-recording bootstrap;
  // Plan 04-04 REVISION iter-2 Option B; verified via existing harness surface).
  await page.evaluate(async () => {
    const harness = (window as unknown as {
      __mokoshHarness: { assertA2: () => Promise<{ passed: boolean; error?: string }> };
    }).__mokoshHarness;
    const a2 = await harness.assertA2();
    if (!a2.passed) {
      throw new Error(`assertA2 priming failed: ${a2.error ?? '(no error)'}`);
    }
  });
  r.diagnostics.push('Step 1 OK: assertA2 prime -> REC');

  // Step 2: 5-min wall-clock idle.
  r.diagnostics.push(`Step 2: waiting ${A33_IDLE_WAIT_MS}ms for SW idle window`);
  await new Promise((res) => setTimeout(res, A33_IDLE_WAIT_MS));

  // Step 3: force SW termination via CDP.
  await stopServiceWorker(browser, extensionId);
  r.diagnostics.push('Step 3 OK: SW terminated via worker.close()');

  // Step 4: brief settle for SW teardown.
  await new Promise((res) => setTimeout(res, A33_NEW_SW_BOOT_MS));

  // Step 5: SAVE_ARCHIVE inline dispatch from harness-page realm
  // (Plan 04-04 REVISION iter-2 Option B; wakes SW event-driven).
  const saveResult = await page.evaluate(
    (timeoutMs: number) =>
      new Promise<{ success: boolean; error?: string }>((resolve) => {
        const timer = setTimeout(() => {
          resolve({ success: false, error: `SAVE_ARCHIVE timed out after ${timeoutMs}ms` });
        }, timeoutMs);
        chrome.runtime.sendMessage({ type: 'SAVE_ARCHIVE' }, (response: unknown) => {
          clearTimeout(timer);
          if (chrome.runtime.lastError !== undefined) {
            resolve({ success: false, error: String(chrome.runtime.lastError.message) });
            return;
          }
          resolve(response as { success: boolean; error?: string });
        });
      }),
    A33_SAVE_ARCHIVE_TIMEOUT_MS,
  );
  r.checks.push({
    name: 'A33.1: SAVE_ARCHIVE ack success after 5-min idle + SW kill',
    expected: true,
    actual: saveResult.success,
    passed: saveResult.success === true,
  });

  // Step 6: settle for chrome.downloads to finish.
  await new Promise((res) => setTimeout(res, A33_DOWNLOAD_SETTLE_MS));

  // Step 7: locate zip + measure video entry.
  const zipPath = findLatestZip(downloadsDir);
  if (zipPath === null) {
    r.checks.push({ name: 'A33.0: zip present', expected: '>=1 zip', actual: 'none', passed: false });
    r.passed = false;
    return r;
  }
  const zip = await JSZip.loadAsync(readFileSync(zipPath));
  const videoEntry = zip.file('video/last_30sec.webm');
  const videoSize = videoEntry !== null
    ? (await videoEntry.async('uint8array')).byteLength
    : 0;
  r.checks.push({
    name: 'A33.2: video/last_30sec.webm size > 0 (buffer survived SW eviction)',
    expected: '>0',
    actual: String(videoSize),
    passed: videoSize > 0,
  });
  r.checks.push({
    name: 'A33.3: video size > 100 KB (sanity floor; real archives 1-3 MB)',
    expected: `>${A33_VIDEO_SIZE_FLOOR_BYTES}`,
    actual: String(videoSize),
    passed: videoSize > A33_VIDEO_SIZE_FLOOR_BYTES,
  });

  r.passed = r.checks.every((c) => c.passed);
  return r;
}

From tests/uat/harness.test.ts:486 (orchestrator drivers-array — append site for A33):

// Plan 04-08 — driveA33 lands HERE, after the existing A32 entry at line 486.
{
  name: 'A33',
  drive: process.env.SKIP_LONG_UAT === '1'
    ? async (): Promise<AssertionRecord> => ({
        name: 'A33',
        passed: true,
        checks: [],
        diagnostics: ['A33 SKIPPED (SKIP_LONG_UAT=1; unset to run 5-min idle test)'],
      })
    : driveA33Wrapped,
},

From tests/fixtures/last_30sec.webm (existing internal project artifact — candidate fixture source):

• size: 1.9 MB
• codec: VP9
• dimensions: 1142x1044
• license: internal project capture (CC0-equivalent project-owned)
• A direct copy/symlink to tests/uat/fixtures/synthetic-display-source.webm is the simplest baseline; the executor MAY regenerate a smaller/looped/cleaner WebM via ffmpeg if preferred. Either choice satisfies the >=1 MB + VP9 + >=30s contract.

Task 1: Bundle WebM fixture + replace canvas.captureStream with HTMLVideoElement.captureStream in installFakeDisplayMedia() tests/uat/fixtures/synthetic-display-source.webm, src/test-hooks/offscreen-hooks.ts, globals.d.ts, manifest.json, vite.config.ts, vite.test.config.ts src/test-hooks/offscreen-hooks.ts (full file — installFakeDisplayMedia at lines 139-264 + uninstallFakeDisplayMedia at 271-291), src/welcome/welcome.ts:30-50 (Vite ?url import precedent), globals.d.ts (full — ambient module declaration pattern), manifest.json (full — web_accessible_resources block at line 20), vite.config.ts (full — rollupOptions.input + nodePolyfills config), vite.test.config.ts (full — test-build entry mirror), tests/fixtures/last_30sec.webm (verify file exists + VP9 codec + ~1.9 MB), tests/uat/spike-a33-sw-persistence.ts (full — to understand the exact prime + SAVE flow the new methodology will be tested against), .planning/debug/sw-offscreen-persistence-investigation-session-2.md (Resolution section — fix recommendations) **Step 1 — Bundle the WebM fixture.** - Create directory: `mkdir -p tests/uat/fixtures/`. - Copy `tests/fixtures/last_30sec.webm` to `tests/uat/fixtures/synthetic-display-source.webm`. The existing artifact is a 1.9 MB VP9 WebM internally captured by this project's MediaRecorder pipeline — CC0-equivalent project-owned per the "internal capture" provenance documented in `.planning/STATE.md` Phase 1 Closure Notes. Verify codec via `ffprobe -v error -show_entries stream=codec_name,width,height -of default=nw=1 tests/uat/fixtures/synthetic-display-source.webm` reports `codec_name=vp9`. - The fixture must be >=1 MB AND >=30 seconds duration (loopable). The existing 1.9 MB capture satisfies size; duration is `N/A` per ffprobe (live-capture WebM lacks a duration tag), BUT the 1.9 MB VP9 at 400 kbps yields ~38s of decoded timeline — sufficient for the 5-min spike via `videoEl.loop = true`. If the executor wants a stricter contract, regenerate via `ffmpeg -f lavfi -i testsrc=duration=35:size=320x180:rate=30 -c:v libvpx-vp9 -b:v 400k tests/uat/fixtures/synthetic-display-source.webm` (this is OPTIONAL — the copy baseline works; only regenerate if the copy's duration tag is load-bearing for the chosen tests). - Decision (per `feedback-no-unilateral-scope-reduction.md`): the executor's default is the COPY path (zero-cost, project-owned, already proven to play in Chrome per Plan 01-07). Regeneration is an OPTIONAL upgrade if the baseline fails to loop cleanly in headless captureStream.

Step 2 — Add ambient module declaration for *.webm?url.

• Edit globals.d.ts. After the existing declare module '*.svg?url' { ... } block at lines 34-37, append:

  // Plan 04-08 — Vite `?url` import for bundled test-only WebM fixture
  // (tests/uat/fixtures/synthetic-display-source.webm). Mirrors the
  // Plan 01-10 mokosh-mark.svg precedent; only gated test builds resolve
  // the import (offscreen-hooks.ts is tree-shaken in production per
  // `__MOKOSH_UAT__`).
  declare module '*.webm?url' {
    const url: string;
    export default url;
  }
  

Step 3 — Rewrite installFakeDisplayMedia() to use HTMLVideoElement.captureStream.

• Edit src/test-hooks/offscreen-hooks.ts at lines 139-264.
• Add top-of-module import (after existing imports):

  // Plan 04-08 — bundled WebM source for HTMLVideoElement-backed MediaStream.
  // Replaces the prior canvas.captureStream(30) source which was throttled
  // to 0 frames/segment under 5-min headless Chromium idle (Chrome bug
  // 653548; debug session-2 verdict 2026-05-22). The video file's real
  // decoded frame timeline is not subject to invisible-canvas throttling.
  //
  // The `?url` import resolves to a Vite-emitted hashed asset URL only in
  // test builds (offscreen-hooks.ts is gated by `__MOKOSH_UAT__` in
  // src/offscreen/recorder.ts and tree-shaken in production).
  //
  // References:
  //   - .planning/debug/sw-offscreen-persistence-investigation-session-2.md
  //   - https://developer.mozilla.org/docs/Web/API/HTMLMediaElement/captureStream
  //   - Chrome bug 653548: https://bugs.chromium.org/p/chromium/issues/detail?id=653548
  import syntheticDisplaySourceUrl from '../../tests/uat/fixtures/synthetic-display-source.webm?url';
  

• Replace the installFakeDisplayMedia body (lines 139-264). Preserve:
  • Idempotency guard (if (fakeInstalled) return;).
  • The lastGetDisplayMediaConstraints capture (A23 contract).
  • The displaySurface monkey-patch via patchDisplaySurface(stream).
  • The mintStream() factory pattern (fresh MediaStream per getDisplayMedia call).
  • The fakeGetDisplayMedia function shape (cast-through-unknown to assign to navigator.mediaDevices.getDisplayMedia).
• Replace canvas creation with HTMLVideoElement creation:

  // Build a hidden HTMLVideoElement playing the bundled WebM source.
  // The element stays off-screen (-9999px) so it has zero visual side
  // effect; loop=true ensures source frames never run out across the
  // 5-min spike window; muted=true is required for autoplay per the
  // Chrome autoplay policy (audio policy doesn't gate muted video).
  const videoEl = document.createElement('video');
  videoEl.src = syntheticDisplaySourceUrl;
  videoEl.loop = true;
  videoEl.muted = true;
  videoEl.autoplay = true;
  videoEl.playsInline = true;
  videoEl.style.position = 'fixed';
  videoEl.style.top = '-9999px';
  videoEl.style.left = '-9999px';
  document.body.appendChild(videoEl);
  fakeVideoEl = videoEl;
  
  // Wait for first-frame readiness so captureStream returns live tracks
  // (not stalled tracks awaiting decode). canplay = readyState >= 3
  // (HAVE_FUTURE_DATA). Reject path drops a single explicit error so a
  // misconfigured fixture surfaces immediately (rather than producing a
  // mysterious 0-frames downstream).
  await new Promise<void>((resolve, reject) => {
    const onCanPlay = (): void => {
      videoEl.removeEventListener('canplay', onCanPlay);
      videoEl.removeEventListener('error', onError);
      resolve();
    };
    const onError = (): void => {
      videoEl.removeEventListener('canplay', onCanPlay);
      videoEl.removeEventListener('error', onError);
      reject(new Error('synthetic-display-source.webm failed to load'));
    };
    videoEl.addEventListener('canplay', onCanPlay);
    videoEl.addEventListener('error', onError);
  });
  
  // Explicit .play() — autoplay attr is best-effort; .play() returns a
  // Promise that resolves once playback starts. Headless Chrome reliably
  // honors muted-autoplay but the explicit call removes any policy edge.
  await videoEl.play();
  

• Delete the canvas + ctx + drawFrame + requestAnimationFrame + setInterval block (lines 160-199 in current source). The video-file source provides frames inherently — no synthetic frame driver needed.
• Update mintStream() to call videoEl.captureStream(30) instead of canvas.captureStream(30):

  const mintStream = (): MediaStream => {
    // HTMLVideoElement.captureStream(30) — the source video's frame
    // timeline drives cadence; the 30 fps argument is the requested
    // upper bound. The track's getSettings() reports the resolved
    // frameRate after capture begins.
    //
    // TypeScript cast through unknown because HTMLMediaElement.captureStream
    // is not in the default lib.dom.d.ts at all versions (it's a non-
    // standard but widely-implemented method; the cast pins our reliance
    // on the runtime surface).
    const stream = (videoEl as HTMLVideoElement & {
      captureStream: (fps?: number) => MediaStream;
    }).captureStream(30);
    patchDisplaySurface(stream);
    return stream;
  };
  

• Update module-level state declarations:

  // Replace: let fakeCanvas: HTMLCanvasElement | null = null;
  // Replace: let fakeAnimationHandle: number | null = null;
  // Replace: let fakeDrawInterval: ReturnType<typeof setInterval> | null = null;
  // With:
  let fakeVideoEl: HTMLVideoElement | null = null;
  

• Note: installFakeDisplayMedia() becomes async (it now awaits the canplay event + .play()). The existing module-load eager call at the bottom of the file (lines 533-537) wraps in try/catch — update to either: (a) void installFakeDisplayMedia().catch(...) OR (b) leave the try/catch but accept that the wrapper now logs the rejection. Recommendation: option (a) for explicit fire-and-forget semantics; the bridge op install-fake-display-media (line 408-418) already awaits-and-responds properly.
• Update the bridge handler at lines 408-418 to await the async install:

  if (op === 'install-fake-display-media') {
    try {
      await installFakeDisplayMedia();
      sendResponse({ ok: true });
    } catch (err) {
      sendResponse({
        ok: false,
        error: err instanceof Error ? err.message : String(err),
      });
    }
    return true;  // signal async response (was false; required for await)
  }
  

  Note: the listener's outer signature must allow return true for async ops — verify by checking neighboring ops; the listener returns false for sync, true for async. Update the wrapper to match the async contract.

Step 4 — Update uninstallFakeDisplayMedia() to teardown the video element.

• Edit src/test-hooks/offscreen-hooks.ts at lines 271-291. Replace canvas cleanup with video cleanup:

  export function uninstallFakeDisplayMedia(): void {
    if (!fakeInstalled) {
      return;
    }
    fakeInstalled = false;
    if (fakeVideoEl !== null) {
      try {
        fakeVideoEl.pause();
      } catch {
        // ignore pause errors during teardown
      }
      fakeVideoEl.remove();
      fakeVideoEl = null;
    }
    // We deliberately do NOT restore the original getDisplayMedia — the
    // offscreen document is throwaway and gets a fresh navigator on the
    // next createDocument() anyway.
  }
  

Step 5 — Bundle gating (decide if WAR entry needed).

• The Vite ?url import resolves the WebM via Vite's asset pipeline. For the offscreen document (which is loaded by chrome.offscreen.createDocument({url: 'src/offscreen/index.html', ...})), the ?url import emits the asset to dist-test/assets/<hash>.webm and @crxjs/vite-plugin auto-generates a web_accessible_resources entry for the offscreen-reachable asset (same pattern as Plan 01-10 mokosh-mark.svg per the existing welcome.ts precedent).
• Decision (executor verifies during Step 6 verify): if @crxjs/vite-plugin auto-WARs the asset (high confidence per Plan 01-10 precedent + Plan 01-12 RESEARCH §155), NO manifest.json edit is required. If WAR auto-generation fails (verified by grep of the test-build dist-test/manifest.json post-build), add an explicit entry:

  {
    "resources": ["assets/*.webm"],
    "matches": ["<all_urls>"]
  }
  

  The decision is captured in the SUMMARY; the BASELINE is "no manifest edit needed" per the existing analog.

Step 6 — Update Vite configs if necessary.

• vite.config.ts: production build — verify nothing changes. The test-hooks module is tree-shaken in production per __MOKOSH_UAT__; the ?url import resolves only in the test build.
• vite.test.config.ts: test build — verify the existing rollupOptions covers the offscreen entry (it already does per Plan 01-13). No new rollupOptions entry needed; the ?url import is a side-effect of the offscreen-hooks.ts module being included in the test build via the existing gated dynamic import at src/offscreen/recorder.ts:46-48.

Step 7 — Verify TypeScript + production build clean.

• npx tsc --noEmit exits 0.
• npm run build exits 0 (production build; test-hooks tree-shake verified — grep -c 'synthetic-display-source' dist/ returns 0 across all production chunks).
• npm run build:test exits 0 (test build; ?url import resolves to hashed asset in dist-test/; grep -l 'synthetic-display-source\.webm' dist-test/ returns ≥ 1 hit pointing at the offscreen chunk).
• wc -c tests/uat/fixtures/synthetic-display-source.webm reports ≥ 1_000_000 bytes.
• grep -c "canvas.captureStream\|fakeCanvas\|fakeAnimationHandle\|fakeDrawInterval" src/test-hooks/offscreen-hooks.ts returns 0 (all canvas symbols excised).
• grep -c "videoEl.captureStream\|fakeVideoEl\|HTMLVideoElement" src/test-hooks/offscreen-hooks.ts returns ≥ 3 (replacement symbols present). mkdir -p tests/uat/fixtures && test -s tests/uat/fixtures/synthetic-display-source.webm && wc -c tests/uat/fixtures/synthetic-display-source.webm | awk '$1 > 1000000 {exit 0} {exit 1}' && npx tsc --noEmit && npm run build 2>&1 | tail -5 && npm run build:test 2>&1 | tail -5 && grep -c "synthetic-display-source" dist/ -r 2>/dev/null | grep -v ":0$" | wc -l | awk '$1 == 0 {exit 0} {exit 1}' && grep -c "canvas.captureStream" src/test-hooks/offscreen-hooks.ts | awk '$1 == 0 {exit 0} {exit 1}' && grep -c "videoEl.captureStream|fakeVideoEl" src/test-hooks/offscreen-hooks.ts | awk '$1 >= 2 {exit 0} {exit 1}' <acceptance_criteria>
  • tests/uat/fixtures/synthetic-display-source.webm exists, is VP9, >= 1 MB.
  • globals.d.ts contains the declare module '*.webm?url' block.
  • src/test-hooks/offscreen-hooks.ts imports syntheticDisplaySourceUrl via Vite ?url suffix.
  • installFakeDisplayMedia() is async; awaits videoEl canplay event + videoEl.play() before returning.
  • mintStream() calls videoEl.captureStream(30) (NOT canvas.captureStream).
  • uninstallFakeDisplayMedia() pauses + removes the video element (NOT canvas + RAF + interval cleanup).
  • All 6 existing bridge ops (install-fake-display-media + dispatch-ended + has-stream + get-display-surface + get-segment-count + get-last-getDisplayMedia-constraints) remain functional; the install-fake-display-media op returns true (async dispatcher signal).
  • npx tsc --noEmit exits 0.
  • npm run build exits 0; production bundle has zero references to synthetic-display-source OR videoEl.captureStream OR fakeVideoEl (test-hooks tree-shake verified).
  • npm run build:test exits 0; test bundle resolves the ?url import.
  • grep -c "canvas.captureStream" src/test-hooks/offscreen-hooks.ts returns 0.
  • The displaySurface monkey-patch (patchDisplaySurface(stream) call) is preserved.
  • The A23 lastGetDisplayMediaConstraints capture is preserved.
  • The idempotent install/uninstall contract is preserved. </acceptance_criteria> Methodology fix landed; bundled WebM source replaces canvas.captureStream throttling. Atomic commit: feat(04-08): video-file-backed MediaStream — replace canvas.captureStream invisible-source throttling per debug session-2 verdict.

Task 2: Re-run spike-a33-sw-persistence.ts + land A33 harness assertion + orchestrator wiring tests/uat/extension-page-harness.ts, tests/uat/lib/harness-page-driver.ts, tests/uat/harness.test.ts, tests/uat/spike-a33-sw-persistence.ts tests/uat/spike-a33-sw-persistence.ts (full — re-run target), tests/uat/extension-page-harness.ts:3517-3700 (assertA30 — cs-injection-world precedent for reference; A33 does NOT use this pattern but reading clarifies the harness assertion shape), tests/uat/extension-page-harness.ts:3878-3917 (assertA31 — most-recent chrome.runtime.sendMessage SAVE_ARCHIVE pattern; copy this), tests/uat/extension-page-harness.ts:3932-4021 (__mokoshHarness global registration block — verify assertA2 is the canonical "prime fresh recording" entrypoint per Plan 04-04 REVISION iter-2 Option B), tests/uat/lib/harness-page-driver.ts:48-80 (stopServiceWorker helper — REUSED from Plan 04-04 3726eee), tests/uat/lib/harness-page-driver.ts:2039-2148 (driveA30 — host-side filter pattern for shape reference), tests/uat/lib/harness-page-driver.ts:1434-1480 (findLatestZip exported function — REUSED from Plan 04-04), tests/uat/harness.test.ts:100-110 (import block), tests/uat/harness.test.ts:340-360 (wrapped-driver block), tests/uat/harness.test.ts:459-487 (drivers-array push block; A32 is the most-recent entry), tests/uat/harness.test.ts:225-240 (SKIP_PROD_REBUILD env-gate pattern — analog for SKIP_LONG_UAT) **Step 0 — GATING CONDITION (Task 1 complete + methodology valid).** - Verify Task 1 acceptance criteria all met. If any fail (TS error, missing fixture, etc.), STOP and fix before proceeding.

Step 1 — Re-run the spike script.

• Run: HEADLESS=1 SKIP_PROD_REBUILD=0 npx tsx tests/uat/spike-a33-sw-persistence.ts 2>&1 | tee /tmp/04-08-spike-rerun.log
• Total wall-clock: ~6-7 min (5 min idle + ~1-2 min orchestration).
• Expected outcome: SPIKE OUTCOME: PASSED with videoSize > 100_000 (typical 1-3 MB).
• GATING CONDITION for landing A33: grep -c 'SPIKE OUTCOME: PASSED' /tmp/04-08-spike-rerun.log returns ≥ 1 AND extracted videoSize > 100_000.
• If the re-run still FAILS (videoSize ≤ 100_000): STOP execution; document failure in SUMMARY; flag for further debug session. This branch is unlikely per session-2 verdict (canvas throttling is the only identified root cause; HTMLVideoElement source bypasses it definitively per MDN + Chrome bug 653548 design doc) but the spike-first contract requires explicit acknowledgement of the FAIL branch.

Step 2 — Update the spike script to use assertA2 prime as canonical (cleanup).

• Per debug session-2 Step B addition, the spike already uses __mokoshHarness.assertA2 for the prime step. No edit needed — but verify the script's PROBE 1 (POST-PRIME) returns count=0 AND PROBE 2 (PRE-KILL after 5min idle) returns count=3 AND PROBE 3 (POST-KILL) returns count=3. The PRE-KILL=3 vs the previous PRE-KILL=3-but-frames=0 distinguishes "segments existed AND have frames" (PASSING methodology) from "segments existed but zero frames" (canvas throttling). The videoSize > 100_000 outcome IS the methodology success indicator.

Step 3 — Land A33 in the harness (3-file lockstep per Plan 04-04 Wave 1 spec verbatim).

File A: tests/uat/extension-page-harness.ts — no edits needed (per Plan 04-04 REVISION iter-2 Option B). The __mokoshHarness surface stays at assertA1..A31 + getManifestVersion. SAVE_ARCHIVE dispatch happens inline in driveA33 via page.evaluate + chrome.runtime.sendMessage. The Task 2 read_first MUST verify this; if a different prime-recording method is more appropriate than assertA2, document in SUMMARY but DO NOT add new __mokoshHarness methods (FORBIDDEN_HOOK_STRINGS lockstep at 12 entries).

File B: tests/uat/lib/harness-page-driver.ts — append driveA33 per the body in <interfaces> above.

• Place AFTER the existing driveA32 function definition (the most-recent Phase 3 addition).
• Verify the stopServiceWorker helper (lines 68-80) is already in scope — it is, per Plan 04-04 commit 3726eee.
• Verify findLatestZip is in scope (exported at line 1434) — it is, per Plan 04-04 commit 3726eee.
• Verify JSZip + readFileSync are imported (lines 37 + 41) — they are.
• Type signature: (page: Page, browser: Browser, extensionId: string, downloadsDir: string) => Promise<AssertionRecord>.
• Filter-pipeline form; no continue; explicit named callbacks per project style.

File C: tests/uat/harness.test.ts — 3 sites edit:

(1) Import block at line 107 — add driveA33, after driveA32,:

// Plan 04-08 — driveA33 SW state persistence (ROADMAP SC #1; methodology
// reframe per debug session-2 verdict; needs Browser + extensionId for
// CDP-based SW kill + downloadsDir for host-side JSZip parse).
driveA33,

(2) Wrapped-driver block after line 357 (after driveA31Wrapped):

// Plan 04-08 — driveA33 needs Browser + extensionId for CDP-based SW kill
//             AND downloadsDir for host-side JSZip parse of post-restart zip.
const driveA33Wrapped: (page: import('puppeteer').Page) => Promise<AssertionRecord> =
  (page) => driveA33(page, handles.browser, handles.extensionId, handles.downloadsDir);

(3) Drivers-array push at line 487 (after the existing A32 entry):

// Plan 04-08 A33: SW state persistence 5-min idle (ROADMAP SC #1).
// Methodology reframe per debug session-2 — video-file MediaStream
// replaces the canvas.captureStream invisible-source throttling that
// produced 8505-byte 0-frames archives under the previous Plan 04-04
// spike methodology. Architecture (offscreen-RAM segments: Blob[]) is
// unchanged and canonically correct per debug session-2 segment-count
// probe evidence (POST-KILL count=3 confirms structural persistence).
// Forces SW eviction via Puppeteer CDP worker.close() per the canonical
// Chrome devrel pattern (stopServiceWorker helper from Plan 04-04).
// Env-gated by SKIP_LONG_UAT for fast per-commit iteration; defaults
// to RUN for Phase 4 closure + alpha gate.
{
  name: 'A33',
  drive: process.env.SKIP_LONG_UAT === '1'
    ? async (): Promise<AssertionRecord> => ({
        name: 'A33',
        passed: true,
        checks: [],
        diagnostics: ['A33 SKIPPED (SKIP_LONG_UAT=1; unset to run 5-min idle test)'],
      })
    : driveA33Wrapped,
},

Step 4 — Run the UAT harness verification gates.

• npx tsc --noEmit exits 0.
• npm run build:test exits 0.
• Skip-mode UAT (fast preserve): HEADLESS=1 SKIP_PROD_REBUILD=1 SKIP_LONG_UAT=1 npm run test:uat 2>&1 | tail -5 | tee /tmp/04-08-uat-skip.log — expect 34/34 GREEN in ~95s; A33 SKIPPED placeholder counts as PASS.
• Full-mode UAT (closure gate): HEADLESS=1 SKIP_PROD_REBUILD=1 npm run test:uat 2>&1 | tail -5 | tee /tmp/04-08-uat-full.log — expect 34/34 GREEN in ~6.5 min; A33 actually runs and passes A33.1 + A33.2 + A33.3.

Step 5 — Lockstep + bundle-gate invariant verification.

• Tier-1 FORBIDDEN_HOOK_STRINGS inventory unchanged at 12 — verify by wc -l of both arrays returns the same count pre/post-edit:

  # tests/uat/harness.test.ts:123-138 = 12 entries
  # tests/background/no-test-hooks-in-prod-bundle.test.ts:108-... = 12 entries (matching)
  grep -c "^[[:space:]]*'" tests/uat/harness.test.ts | head -1  # context-sensitive; check post-edit
  

  Confirm zero new entries added (no new MOKOSH_UAT-gated symbols).
• Pre-checkpoint bundle gates (per feedback-pre-checkpoint-bundle-gates.md) — 6/6 PASS unchanged from Plan 04-03 baseline:
  • grep -c 'new Function' dist/assets/index-*.js returns 0 (Plan 04-02 polarity preserved)
  • grep -c 'eval' dist/assets/index-*.js returns 0
  • grep -c 'Buffer\.' dist/assets/index-*.js returns 1 (pre-existing JSZip polyfill; Plan 04-02 deferred)
  • grep -c 'window\.' dist/assets/index-*.js returns 0 (SW chunk DOM-globals)
  • grep -c 'document\.' dist/assets/index-*.js returns 0
  • Manifest validation + en/ru parity preserved (unchanged from Plan 04-03)
• vitest baseline preserved: npm test 2>&1 | tail -5 — expect 183/183 GREEN (or 180/183 with the 3 documented pre-existing parallel-vitest flakes per 04-CONTEXT items 9-10; flakes pass in isolation).

Step 6 — Write Plan 04-08 SUMMARY.

• Create .planning/phases/04-harden-clean-up-optional/04-08-SUMMARY.md:
  • Methodology reframe rationale (cite debug session-2 verdict verbatim)
  • Bundled WebM fixture decision (copy vs regenerate; size + codec evidence)
  • installFakeDisplayMedia diff summary (canvas -> HTMLVideoElement; 6 bridge ops preserved; A23 capture preserved)
  • Spike re-run evidence (videoSize before/after; segment-count probe values; elapsed time)
  • A33 land evidence (driveA33 + orchestrator wiring; FORBIDDEN_HOOK_STRINGS at 12; pre-checkpoint gates 6/6)
  • UAT before/after (33/33 -> 34/34 GREEN)
  • ROADMAP SC #1 closure with commit ref
  • Plan 04-04 SUMMARY post-debug amendment cross-reference
  • Persisting artifacts (stopServiceWorker + spike script + canonical methodology pattern)
  • Architectural integrity statement (offscreen-RAM segments: Blob[] is UNCHANGED and canonically correct)

Step 7 — Update STATE.md + ROADMAP.md markers (Phase 4 partial closure).

• STATE.md: append to "Decisions" section: [Phase 04-08]: Methodology reframe complete — video-file MediaStream replaces canvas.captureStream throttling per debug session-2 verdict; A33 harness assertion landed; UAT 33 -> 34 GREEN; ROADMAP SC #1 (SW state persistence) CLOSED.
• ROADMAP.md: flip Phase 4 SC #1 row from "STATUS 2026-05-21: OPEN" to "STATUS 2026-05-22: CLOSED via Plan 04-08 — see .planning/phases/04-harden-clean-up-optional/04-08-SUMMARY.md". Add Plan 04-08 row to the Plans list with brief objective.

Step 8 — Atomic commit.

• Single atomic commit with all Task 2 + Task 3 artifacts: feat(04-08): A33 SW state persistence harness assertion — methodology reframe (34/34 GREEN; ROADMAP SC #1 CLOSED). npx tsc --noEmit && npm run build:test && HEADLESS=1 SKIP_PROD_REBUILD=1 SKIP_LONG_UAT=1 npm run test:uat 2>&1 | tail -5 | tee /tmp/04-08-uat-skip.log; grep -c '34/34|34 passed' /tmp/04-08-uat-skip.log | awk '$1 >= 1 {exit 0} {exit 1}' && grep -c 'driveA33' tests/uat/harness.test.ts | awk '$1 >= 3 {exit 0} {exit 1}' && grep -c 'SKIP_LONG_UAT' tests/uat/harness.test.ts | awk '$1 >= 2 {exit 0} {exit 1}' && grep -c 'dispatchSaveArchive' tests/uat/lib/harness-page-driver.ts tests/uat/extension-page-harness.ts tests/uat/harness.test.ts 2>/dev/null | grep -v ":0$" | wc -l | awk '$1 == 0 {exit 0} {exit 1}' <acceptance_criteria>
  • Spike re-run output contains SPIKE OUTCOME: PASSED AND videoSize > 100_000. (If FAILED branch fires, STOP and document; A33 land is BLOCKED.)
  • npx tsc --noEmit exits 0.
  • npm run build:test exits 0.
  • tests/uat/lib/harness-page-driver.ts contains driveA33 function with the 4-arg signature (page, browser, extensionId, downloadsDir) => Promise<AssertionRecord>.
  • tests/uat/lib/harness-page-driver.ts driveA33 dispatches SAVE_ARCHIVE inline via chrome.runtime.sendMessage({type: 'SAVE_ARCHIVE'}, ...) — verify grep -c "type: 'SAVE_ARCHIVE'" tests/uat/lib/harness-page-driver.ts returns ≥ 1.
  • tests/uat/harness.test.ts imports driveA33 (1 line; grep -c returns ≥ 4 including comment).
  • tests/uat/harness.test.ts defines driveA33Wrapped const.
  • tests/uat/harness.test.ts drivers-array contains an { name: 'A33', drive: ... } entry with SKIP_LONG_UAT env-gate.
  • Skip-mode UAT: HEADLESS=1 SKIP_PROD_REBUILD=1 SKIP_LONG_UAT=1 npm run test:uat reports 34/34 GREEN in ~95s.
  • Full-mode UAT: HEADLESS=1 SKIP_PROD_REBUILD=1 npm run test:uat reports 34/34 GREEN in ~6.5 min; A33.1 + A33.2 + A33.3 all PASS.
  • dispatchSaveArchive symbol is NOT introduced anywhere — grep -c 'dispatchSaveArchive' tests/uat/ returns 0.
  • FORBIDDEN_HOOK_STRINGS inventory unchanged at 12 entries — verify by line count of both arrays.
  • Pre-checkpoint bundle gates 6/6 PASS unchanged from Plan 04-03 baseline.
  • vitest 183 baseline preserved (or 180/183 with the 3 documented pre-existing flakes; pass in isolation).
  • .planning/phases/04-harden-clean-up-optional/04-08-SUMMARY.md exists with: methodology rationale + spike re-run evidence + A33 land evidence + UAT before/after + ROADMAP SC #1 closure + cross-reference to Plan 04-04 post-debug amendment.
  • .planning/STATE.md Decisions list contains a Plan 04-08 entry citing ROADMAP SC #1 CLOSED.
  • .planning/ROADMAP.md Phase 4 SC #1 row flipped from OPEN to CLOSED with date + Plan 04-08 cite. </acceptance_criteria> A33 lands; UAT 33->34 GREEN; ROADMAP SC #1 CLOSED. Atomic commit: feat(04-08): A33 SW state persistence harness assertion — methodology reframe (34/34 GREEN; ROADMAP SC #1 CLOSED).

<threat_model>

Trust Boundaries

Boundary	Description
Bundled WebM fixture -> offscreen test bundle	the tests/uat/fixtures/synthetic-display-source.webm is project-owned (CC0-equivalent internal capture) and loaded via Vite's ?url asset pipeline only in test builds. Production builds tree-shake the entire offscreen-hooks module per __MOKOSH_UAT__; the fixture has zero attack surface in production.
HTMLVideoElement.captureStream -> MediaRecorder	the video element source is bundled at build time (not network-fetched); no remote-origin attack vector. The captured stream feeds the production MediaRecorder code path verbatim — same boundary as canvas.captureStream had.
Puppeteer CDP -> Chrome MV3 SW	unchanged from Plan 04-04 (stopServiceWorker helper reused verbatim).

STRIDE Threat Register

Threat ID	Category	Component	Disposition	Mitigation Plan
T-04-08-01	Tampering	future change to installFakeDisplayMedia() reintroduces canvas.captureStream silently	mitigate	grep -c "canvas.captureStream" src/test-hooks/offscreen-hooks.ts invariant = 0 codified in Task 1 verify. A33 acts as a regression-catching gate; if a future PR moves source back to canvas, the spike fails fast (videoSize=8505).
T-04-08-02	Tampering	bundled synthetic-display-source.webm is renamed/deleted/replaced with a tiny or invalid WebM	mitigate	Task 1 verify checks wc -c >= 1_000_000 bytes; Task 2 spike re-run catches any content-level corruption (videoSize-floor gate).
T-04-08-03	Information disclosure	the bundled WebM contains operator content (it's a project-internal capture of the developer's screen)	accept	The existing tests/fixtures/last_30sec.webm has been in the repo since 2026-05-15 (Plan 01-07 closure); the new copy at tests/uat/fixtures/synthetic-display-source.webm is the same project-owned artifact. Tradeoff: rebuilding a fresh WebM from ffmpeg -f lavfi -i testsrc is OPTIONAL per Task 1 Step 1. If the developer prefers content-free fixtures, the regeneration path is the documented escape hatch.
T-04-08-04	DoS (test runtime)	A33's 5-min idle adds ~5 min to harness wall-clock (95s -> 395s); per-commit CI lanes would suffer	mitigate	Env-gated by SKIP_LONG_UAT=1 (default RUN for closure + alpha; documented per-commit fast-skip path). Same gate Plan 04-04 specified.
T-04-08-05	Repudiation	HTMLVideoElement.captureStream is non-standard (not in lib.dom.d.ts at all TS versions); a TS strict-mode bump could break the cast-through-unknown idiom	accept	The cast is pinned in the code at Task 1 Step 3; project's TS pin is documented; if a TS upgrade ever breaks the cast, the build-test gate (Task 1 verify) catches it. The runtime surface itself (HTMLMediaElement.captureStream) is implemented in Chrome since 2017 and stable per MDN.
T-04-08-06	Spoofing	a malicious replacement synthetic-display-source.webm could inject malicious VP9 codec data	accept	the fixture is committed to git; any tamper is visible via git diff. Plan 04-08's threat surface is test-only and the test build runs in a sandboxed Puppeteer browser instance. No production user is exposed.
</threat_model>

- `npx tsc --noEmit` exits 0. - `npm run build` exits 0 (production; test-hooks tree-shake verified). - `npm run build:test` exits 0 (test; ?url import resolves). - `wc -c tests/uat/fixtures/synthetic-display-source.webm` reports >= 1_000_000 bytes; codec=vp9 per ffprobe. - `grep -c "canvas.captureStream" src/test-hooks/offscreen-hooks.ts` returns 0. - `grep -c "videoEl.captureStream\|fakeVideoEl" src/test-hooks/offscreen-hooks.ts` returns >= 2. - `grep -c "synthetic-display-source" dist/ -r` returns 0 (production tree-shake). - Spike re-run: `HEADLESS=1 npx tsx tests/uat/spike-a33-sw-persistence.ts` exits 0 with `videoSize > 100_000` (typical 1-3 MB). - UAT harness count 33 -> 34. - Skip-mode UAT: `HEADLESS=1 SKIP_PROD_REBUILD=1 SKIP_LONG_UAT=1 npm run test:uat` GREEN 34/34 in ~95s. - Full-mode UAT: `HEADLESS=1 SKIP_PROD_REBUILD=1 npm run test:uat` GREEN 34/34 in ~6.5 min. - ROADMAP SC #1 row flipped from OPEN to CLOSED (Plan 04-08 cite + 2026-05-22 date). - Tier-1 FORBIDDEN_HOOK_STRINGS lockstep at 12 entries (unchanged). - Pre-checkpoint bundle gates 6/6 PASS (new Function=0 + eval=0 + Buffer.=1 + window.=0 + document.=0 in SW + Tier-1=12 + en/ru parity). - vitest baseline 183 preserved (or 180/183 with 3 documented pre-existing flakes; pass in isolation). - A29 + A30 + A31 + A32 unchanged (no regression to existing assertions). - Architecture invariant preserved: `src/offscreen/recorder.ts:91 let segments: Blob[] = []` UNCHANGED — debug session-2 verdict is honored (NO IndexedDB persistence work). - spike-FAILED forensic-evidence preservation: `tests/uat/spike-a33-sw-persistence.ts` retained (Plan 04-04 commit 3726eee + debug session-2 Step B + C additions); now functions as a PASSING regression test under the new methodology. - `dispatchSaveArchive` symbol NOT introduced anywhere — `grep -c` across spike script + harness files returns 0.

<success_criteria>

• Bundled WebM fixture lands at tests/uat/fixtures/synthetic-display-source.webm (>=1 MB VP9; project-owned).
• installFakeDisplayMedia() rewritten — canvas.captureStream replaced by HTMLVideoElement.captureStream; displaySurface monkey-patch + A23 capture + idempotency contract preserved.
• Ambient module decl for *.webm?url added to globals.d.ts.
• Spike re-run produces videoSize > 100_000 (typical 1-3 MB) — methodology reframe empirically validated.
• A33 harness assertion lands per Plan 04-04 Pattern 4 verbatim: driveA33 + driveA33Wrapped + orchestrator entry + SKIP_LONG_UAT env-gate.
• UAT harness count 33 -> 34 GREEN (skip-mode in ~95s; full-mode in ~6.5 min).
• ROADMAP SC #1 (SW state persistence) flipped CLOSED in ROADMAP.md.
• Plan 04-04 SUMMARY post-debug amendment cross-referenced in Plan 04-08 SUMMARY.
• Tier-1 FORBIDDEN_HOOK_STRINGS inventory unchanged at 12 entries.
• Pre-checkpoint bundle gates 6/6 PASS.
• Architectural integrity preserved (no IndexedDB persistence; no chrome.storage migration; src/offscreen/recorder.ts:91 segments array unchanged).
• vitest 183 baseline preserved.
• Plan 04-04 forensic artifacts (stopServiceWorker helper + spike script) repurposed as PASSING regression tests under valid methodology. </success_criteria>

After completion, create `.planning/phases/04-harden-clean-up-optional/04-08-SUMMARY.md` capturing:

• Methodology reframe rationale — verbatim cite of debug session-2 verdict (REFUTED-architecture; canvas-captureStream issue); explicit rejection of the previously-proposed IndexedDB persistence plan-fix with the empirical reasoning (the spike would STILL produce 8505 bytes after IDB lands because the failure is in the fake stream, not in segment persistence).
• Bundled WebM fixture decision — copy from tests/fixtures/last_30sec.webm vs regenerate via ffmpeg; size + codec + duration evidence; license/provenance attestation (CC0-equivalent project-owned internal capture).
• installFakeDisplayMedia diff summary — before (canvas.captureStream + RAF + setInterval) vs after (HTMLVideoElement + canplay event + .play() + captureStream); preserved invariants (displaySurface monkey-patch, A23 capture, idempotency, 6 bridge ops).
• Spike re-run evidence — videoSize before (8505) vs after (>100_000; typical 1-3 MB); segment-count probe values (POST-PRIME=0, PRE-KILL=3, POST-KILL=3); elapsed time (~308s baseline preserved); SPIKE OUTCOME: PASSED.
• A33 land evidence — driveA33 (4-arg signature); 3-file lockstep diff (extension-page-harness.ts unchanged per Option B; harness-page-driver.ts +driveA33; harness.test.ts +import +wrapped +array push); FORBIDDEN_HOOK_STRINGS at 12 entries (unchanged); pre-checkpoint gates 6/6 PASS.
• UAT before/after — 33/33 -> 34/34 GREEN; skip-mode wall-clock ~95s; full-mode wall-clock ~6.5 min.
• ROADMAP SC #1 closure — flipped OPEN -> CLOSED with Plan 04-08 cite + 2026-05-22 date.
• Plan 04-04 cross-reference — debug session-2 verdict honored; spike-FAILED forensic artifacts (stopServiceWorker helper + spike-a33-sw-persistence.ts) repurposed as PASSING regression tests.
• Architectural integrity statement — let segments: Blob[] = [] at src/offscreen/recorder.ts:91 is UNCHANGED and canonically correct per debug session-2 segment-count probe evidence.
• Commit refs — Task 1 atomic commit (methodology fix) + Task 2 atomic commit (A33 land + SUMMARY + STATE/ROADMAP markers).
• Next plan handoff — Plan 04-07 (closure aggregator) can now reference ROADMAP SC #1 as GREEN; v1 milestone close prep unblocked from the SW persistence side.