Database-backed notifications

Decision

GamePlan stores notification preferences and deduplicated Delivery Attempts in PostgreSQL. A separate Compose worker claims due attempts before making any Discord API call. It never retries an attempt once claimed, because Discord message creation is not idempotent and duplicate player notifications are worse than a recorded failed delivery in pre-alpha.

Consequences

The app remains self-hostable with Docker Compose and no external queue. Failed or interrupted attempts remain visible in the database rather than silently creating duplicate DMs after a worker restart.