- CleanExpired: split into two phases — collect expired entries under
lock, then delete files after releasing the lock to minimize contention
- CleanExpired: guard against zero MaxAge (no-op if unconfigured)
- CleanExpired: log file removal errors instead of silently ignoring
- Start: protect with startOnce to prevent multiple goroutines
- Stop: rename once -> stopOnce for clarity
- cmd_gateway: call mediaStore.Stop() on error path after Start()
- Add TestCleanExpiredZeroMaxAge and double-Start test
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>