Queue cancellation mechanism:
- Add CancelByAlertIDs method to mark queued notifications as cancelled when alerts resolve
- Update CancelAlert to cancel queued notifications containing resolved alert IDs
- Skip cancelled notifications in queue processor
- Prevents resolved alerts from triggering notifications after they clear
Atomic DB operations:
- Add IncrementAttemptAndSetStatus to atomically update attempt counter and status
- Replace separate IncrementAttempt + UpdateStatus calls with single atomic operation
- Prevents orphaned queue entries when crashes occur between operations
- Eliminates race condition where rows get stuck in "pending" or "sending" status
These fixes ensure queued notifications are properly cancelled when alerts resolve
and prevent database inconsistencies during crash scenarios.
Critical fixes (P0):
- Fix cooldown timing: Mark cooldown only after successful delivery, not before enqueue
- Add os.MkdirAll to queue initialization to prevent silent failures on fresh installs
- Add DNS re-validation at webhook send time to prevent DNS rebinding SSRF attacks
- Add SSRF validation for Apprise HTTP URLs
- Remove secret logging (bot tokens, routing keys) from debug logs
- Implement lastNotified cleanup to prevent unbounded memory growth
- Use shared HTTP client for webhooks to enable TLS connection reuse
- Add fallback to direct sending when queue enqueue fails
- Make queue worker concurrent (5 workers with semaphore) to prevent head-of-line blocking
- Fix webhook rate limiter race condition with separate mutex
- Fix email manager thread safety with mutex on rate limiter
- Fix grouping timer leak by adding stopCleanup signal
- Fix webhook 429 double sleep (use Retry-After OR backoff, not both)
Frontend improvements:
- Add queue/DLQ management API methods (getQueueStats, getDLQ, retryDLQItem, deleteDLQItem)
- Add getNotificationHealth and getWebhookHistory endpoints
- Add Apprise test support to NotificationTestRequest type
Related to notification system audit
Remove 4 LLM-generated internal development docs that don't belong in the repository:
- MIGRATION_SCAFFOLDING.md
- NOTIFICATION_AUDIT.md
- NOTIFICATION_QUICK_REFERENCE.md
- NOTIFICATION_SYSTEM_MAP.md
These were internal development notes, not user-facing documentation.
