feat(outbox): harden publish contract with crash-safe idempotency keys

[Banx17]

Overview

This PR hardens the outbox publish contract with crash-safe idempotency keys and comprehensive integration tests. The existing outbox infrastructure (publish idempotency key, lease-based crash recovery, IdempotentConsumer) is already in place - this PR adds integration-level coverage that simulates real crash scenarios to verify the guarantees hold end-to-end.

Related Issue

Closes #945

Changes

Crash-Safe Outbox Integration Tests

• [ADD] tests/integration/outboxCrashRecovery.integration.test.ts
  • Publish idempotency key crash recovery: simulates consumer crash after setting publish_idempotency_key but before markPublished - verifies recovery consumer skips duplicate publish
  • Crash before idempotency key: verifies recovery consumer proceeds with normal publish flow
  • Concurrent idempotency key race: two consumers racing - only one acquires the key
  • Lease lifecycle: claim, lease expiry, reclamation by another consumer, lease renewal, graceful releaseClaims on shutdown
  • Full lifecycle: insert, claim, publish, markPublished end-to-end
  • Poison pill quarantine: malformed events detected and routed to outbox_quarantine
  • Exponential backoff and dead_letter: retry exhaustion and next_attempt_at scheduling
  • Statistics reporting: getStats() verification across all statuses

Idempotent Consumer Key Tests

• Duplicate suppression: idempotency key prevents handler re-execution
• Concurrent deduplication: 5 concurrent calls - handler runs exactly once
• Retry after failure: failed processing allows retry
• Result persistence: isProcessed() and getResult() after processing
• TTL expiry: expired keys allow reprocessing
• Outbox event integration: downstream handler deduplication for outbox events

Verification Results

npm test src/db/outbox/ tests/integration/outboxCrashRecovery.integration.test.ts
63/63 passed (46 existing + 17 new)

Test Files 7 passed (7)
Tests 63 passed (63)

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