When a messaging platform fails to connect at startup (e.g. transient DNS
failure) or disconnects at runtime with a retryable error, the gateway now
queues it for background reconnection instead of giving up permanently.
- New _platform_reconnect_watcher background task runs alongside the
existing session expiry watcher
- Exponential backoff: 30s, 60s, 120s, 240s, 300s cap
- Max 20 retry attempts before giving up on a platform
- Non-retryable errors (bad auth token, etc.) are not retried
- Runtime disconnections via _handle_adapter_fatal_error now queue
retryable failures instead of triggering gateway shutdown
- On successful reconnect, adapter is wired up and channel directory
is rebuilt automatically
Fixes the case where a DNS blip during gateway startup caused Telegram
and Discord to be permanently unavailable until manual restart.
3b509da571