feat: processed-event ledger, idempotent dispatch

crates/domain/src/ports/processed_events.rs

@@ -0,0 +1,16 @@
+use async_trait::async_trait;
+
+use crate::{errors::DomainError, events::EventId};
+
+/// Records which handler has already completed which event, so a redelivered
+/// event does not re-run handlers that succeeded.
+#[async_trait]
+pub trait ProcessedEventLedger: Send + Sync {
+    async fn has_processed(&self, id: &EventId, handler: &str) -> Result<bool, DomainError>;
+
+    /// Idempotent: recording an existing pair is not an error.
+    async fn record_processed(&self, id: &EventId, handler: &str) -> Result<(), DomainError>;
+
+    /// Returns the number of rows removed.
+    async fn delete_older_than(&self, cutoff: chrono::NaiveDateTime) -> Result<u64, DomainError>;
+}