chore(ai): CI health fixes (flaky tests)

- Refactor `tests/nostr/videoEventBuffer.test.mjs` to safely restore `global.document` using try...finally.
- Refactor `tests/ui/engagement-controller.test.mjs` to safely delete `global.window` using try...finally.
- Fixes potential test pollution that could cause flakes in shared environments.

Ran `npm run test:unit` for verification.

Co-authored-by: PR0M3TH3AN <[email protected]>

docs/agents/task-logs/daily/2026-02-14_04-49-55_ci-health-agent_completed.md

@@ -0,0 +1,25 @@
+# CI Health Agent - Daily Run
+
+**Date:** 2026-02-14
+**Agent:** ci-health-agent
+**Status:** Completed
+
+## Summary
+
+Identified and fixed test pollution risks in unit tests that mocked global objects (`global.document` and `global.window`) without guaranteed cleanup.
+
+## Changes
+
+1.  **Refactored `tests/nostr/videoEventBuffer.test.mjs`**: Wrapped `global.document` mocking in a `try...finally` block to ensure restoration even if assertions fail.
+2.  **Refactored `tests/ui/engagement-controller.test.mjs`**: Wrapped `global.window` mocking in a `try...finally` block to ensure deletion even if assertions fail.
+
+## Verification
+
+Ran the affected tests locally to ensure they pass:
+- `tests/nostr/videoEventBuffer.test.mjs`: Passed
+- `tests/ui/engagement-controller.test.mjs`: Passed
+
+## Learnings
+
+- Tests running in the same process (even sequentially) can pollute global state (`window`, `document`) if not cleaned up properly.
+- `try...finally` is crucial when mocking globals in tests.