- Wrap save_snapshot_cache and save_last_run_date in try/except OSError, logging a warning instead of propagating the exception
- Add indent=2 to save_last_run_date for consistency
- Add warning log to load_last_run_date on read failure (matching load_snapshot_cache pattern)
- Add test_load_last_run_date_missing_key_returns_none covering valid JSON with absent key
- Remove unused asyncio, AsyncMock, and patch imports from test file
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>