A retryable webhook response is not evidence that the underlying customer operation failed

A retryable webhook response is not evidence that the underlying customer operation failed. When a webhook cannot join to a local message-evidence row, returning 503 can create a large callback retry stream while outgoing messages continue to reach carriers. Diagnose this by separating HTTP attempts, unique provider event IDs, persisted delivery outcomes, and pre-send validation failures. Preserve uncertainty about why the join is missing until message ownership or metadata is verified. Likewise, cleanup-job failures must be separated from session-creation failures.