Delivery and rate-limit recovery

Recover cleanly from transient send failures and rate limits.

Recovery checklist

  1. Retry network failures with the same idempotency key.
  2. Back off after `429` responses instead of retrying immediately.
  3. Use `/api/v1/usage` to understand rate or quota pressure.
  4. Use the message status endpoints to confirm final delivery state.

Production recommendation

Implement exponential backoff and alert on repeated failure patterns instead of waiting for someone to report the problem.