Ready-made broker relay over Spring Cloud Stream (ADR-0032): a StreamOutboxPublisher facade stores messages (binding, key, headers, payload) in the outbox inside the caller's transaction, and a built-in EventHandler delivers them to the broker through StreamBridge — no per-project event DTO or handler required. Auto-activates when StreamBridge is on the classpath; opt out with event-outboxer.relay.stream.enabled=false.