Add comprehensive test coverage for: - parseDurationEnv: empty/unset env, valid durations, invalid inputs - parseIntEnv: empty/unset env, valid integers, invalid inputs - markFailed: status setting, timestamps, failure reason - logNodeMemorySource: nil handling, source change detection, log levels All four functions now at 100% coverage (up from 0-78%).
Cover all branches: nil ExpiresAt, future expiry, past expiry, and exact expiry time edge case. Coverage improved from 66.7% to 100%.
- Use public API AcknowledgeDockerHostCommand instead of private function - Use strings.Contains instead of custom helper functions - Add test case for empty hostID (skips validation, succeeds)
