A final response generated but not confirmed-delivered was the one
artifact the gateway could lose without a trace: crash or planned
restart between finalize and platform ACK dropped it silently, and the
resume path re-ran the whole turn at full cost (#58818 P1, #41696,
#63695's gateway half).
gateway/delivery_ledger.py records each outbound final response in
state.db (same conventions as the async-delegation ledger: WAL, owner
pid + process-start-time liveness, bounded retention):
pending -> attempting -> delivered | failed
startup sweep on dead-owner rows -> redeliver | abandoned
Contract (the lessons from the closed delivery-outbox attempt #61790):
- obligation recorded BEFORE the first send attempt; cleared only on
SendResult.success (destination acceptance, #51184)
- ambiguity is labeled, never silently retried: rows that were mid-send
when the process died redeliver with a visible '♻️ Recovered reply —
may be a duplicate' prefix (honest at-least-once)
- stable ids from session_key + inbound message id + content, so
distinct threads/topics can never collide
- poison rows bounded: 3 attempts / 24h freshness -> abandoned; claim
atomically re-stamps ownership so racing sweeps can't double-claim
- redelivery clears resume_pending for the session so the resume path
never re-runs a turn whose answer the ledger already holds
- best-effort everywhere: ledger failure can never block or delay a send
- slash-command/ephemeral/empty responses are not recorded; cron and
proactive delivery stay on DeliveryRouter (separate subsystem)
Config: gateway.delivery_ledger (default on; no version bump needed).
Validation: 30 ledger+producer tests; 352 blast-radius gateway tests
green; cross-process E2E (record in process A, kill it mid-send, claim
+ marker + redeliver in a fresh process B against the same state.db).
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