[usrnk1]

Summary

• Attach the desktop startup harness with Playwright's noDefaults: true so observing Electron preserves its native media and focus preferences.
• Document the same requirement for agents attaching to a user's live desktop window.

Cause

Playwright applies light-mode media emulation by default when connectOverCDP attaches to an existing browser. A desktop app following the system theme immediately follows that override, then returns to dark when the connection closes.

The investigation captured a 23 ms dark → light → dark transition with two bright frames, coinciding with another agent's diagnostic attachment. No reload occurred. The fix belongs in the attachment, not in application theme handling; this PR does not change production theme code.

Verification

• Three default Playwright attachments each forced light mode; three attachments with noDefaults: true preserved dark mode with zero media-query changes.
• bun run check — passed (existing lint warnings).
• bun typecheck in packages/app — passed.
• bun test ./e2e/performance/unit/desktop-startup.test.ts in packages/app — 4 passed.
• bun run lint:changed — passed.
• Prettier check and git diff --check — passed.
• bun run typecheck:e2e in packages/app — reports 11 existing errors in unrelated files; reproduced the identical errors on clean origin/dev at 432d870b02.

No investigation probes, screenshots, or other transient artifacts are committed.

[opencodejr]

The change looks sound: the startup harness already fails a run if the desktop theme changes during startup (requireStableTheme). Playwright's default attachment forces light mode, so the attachment itself could trip that check on a dark system. noDefaults: true is supported by the pinned Playwright 1.60.0. The harness doesn't use downloads, so turning off Playwright's other default overrides shouldn't affect it.

I couldn't run it myself, because the benchmark launches the real Electron app and this environment has no display for it. The desktop-startup unit tests pass (4 tests). typecheck:e2e reports 11 errors, none in the changed file, the same count you reported for clean dev.

Public API: unchanged (benchmark harness and AGENTS.md only).

No blocking concerns.

[opencodejr]

The new commit only merges dev into the branch and doesn't change this PR's diff, so my earlier review still applies. Public API: unchanged. No new concerns.