feat: worker relays outbox to nats

crates/domain/src/ports/events.rs

@@ -2,7 +2,7 @@ use async_trait::async_trait;
 
 use crate::{
     errors::DomainError,
-    events::{DomainEvent, EventEnvelope},
+    events::{DomainEvent, EventEnvelope, EventId},
 };
 
 #[async_trait]
@@ -10,6 +10,13 @@ pub trait EventPublisher: Send + Sync {
     async fn publish(&self, event: &DomainEvent) -> Result<(), DomainError>;
 }
 
+/// Delivers one outbox row to the message bus. `Ok` means the bus accepted it
+/// (for a brokered bus: acknowledged), so the row may be marked done.
+#[async_trait]
+pub trait EventRelaySink: Send + Sync {
+    async fn relay(&self, id: Option<&EventId>, event: &DomainEvent) -> Result<(), DomainError>;
+}
+
 pub trait EventConsumer: Send + Sync {
     fn consume(&self) -> futures::stream::BoxStream<'_, Result<EventEnvelope, DomainError>>;
 }