History & DLQ

Every delivery attempt writes a row to /v1/delivery/items with its status, HTTP code, error code, and request/response bodies. Terminal failures (retry ladder exhausted or permanent 4xx) escalate to /v1/delivery/dlq. Both are fully replayable — replay enqueues a new attempt with a fresh idempotency key. Nothing in history is ever mutated; the log is strictly append-only.