saveOutboxMessage

@Transactional
fun saveOutboxMessage(topic: String, key: String, payload: ByteArray, sagaId: String? = null, eventId: String? = null): OutboxMessage(source)

Creates a new outbox message for a raw topic name.

The payload must already be serialized to its on-the-wire form (ByteArray). Encoding (Avro, JSON, …) is the responsibility of the caller — this processor is transport-agnostic.