A distributed messaging guarantee ensuring that each event is processed once and only once, even during network failures.
Exactly-Once Semantics (EoS) guarantees that even if a producer retries publishing a message due to a network timeout, or a consumer restarts after an unexpected crash, the system processes and commits the payload exactly once with zero duplicates and zero data loss.
Guarantees that financial escrow locks, token burns, and carbon certificate minting are never executed more than once per shipment order.
Combines KafkaJS `idempotent: true` (producer sequence numbers + PID) with database transaction upserts (`ON CONFLICT DO NOTHING`) and Redis idempotency intent leases.
EoS requires end-to-end support across producer, transport, and consumer; enabling idempotent producers alone does not guarantee exactly-once database execution.