Fixes 4 test failures identified in pipeline run 239:
1. RunnerJobsService cancel tests:
- Use updateMany mock instead of update (service uses optimistic locking)
- Add version field to mock objects
- Use mockResolvedValueOnce for sequential findUnique calls
2. ActivityService error handling tests:
- Update tests to expect null return (fire-and-forget pattern)
- Activity logging now returns null on DB errors per security fix
3. SecretScannerService unreadable file test:
- Handle root user case where chmod 0o000 doesn't prevent reads
- Test now adapts expectations based on runtime permissions
Quality gates: lint ✓ typecheck ✓ tests ✓
- @mosaic/orchestrator: 612 tests passing
- @mosaic/web: 650 tests passing
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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