webhook_url on submit. When the check reaches a terminal status, we POST once
(with retries on transport / 5xx errors):
type is document_check.{status}: either completed or failed.
Guarantees
- Delivery is at-least-once. Handlers must be idempotent on
data.id. - We stop retrying on
4xx(your endpoint rejected the payload). - Already-delivered checks are not re-posted on Celery retry.