fix: per-handler claim lease in ledger, nats max_deliver, pin handler names

crates/application/tests/worker/worker_test.rs

@@ -477,3 +477,83 @@ async fn duplicate_handler_names_are_rejected() {
     let err = result.err().expect("duplicate names must be rejected");
     assert!(err.to_string().contains("same"), "{err}");
 }
+
+#[tokio::test]
+async fn a_handler_already_running_elsewhere_is_not_run_concurrently() {
+    use domain::ports::{Begin, ProcessedEventLedger};
+    let (handler, calls) = CountingHandler::new("slow", 0);
+    let store = InMemoryStore::new();
+    let id = domain::events::EventId::new();
+    // Another delivery holds a live claim on this (event, handler).
+    assert_eq!(store.begin(&id, "slow").await.unwrap(), Begin::Run);
+    let nacks = Arc::new(Mutex::new(0));
+    let consumer = RedeliveringConsumer {
+        id: Some(id),
+        event: movie_discovered(),
+        times: 1,
+        nacks: Arc::clone(&nacks),
+    };
+
+    WorkerService::new(Arc::new(consumer), vec![handler], store)
+        .unwrap()
+        .run(tokio::sync::watch::channel(false).1)
+        .await;
+
+    assert_eq!(
+        *calls.lock().unwrap(),
+        0,
+        "must not run beside the claim holder"
+    );
+    assert_eq!(*nacks.lock().unwrap(), 1, "delivery is retried later");
+}
+
+#[tokio::test]
+async fn a_stale_in_progress_claim_is_taken_over() {
+    use domain::ports::HANDLER_LEASE_SECONDS;
+    let (handler, calls) = CountingHandler::new("crashed", 0);
+    let store = InMemoryStore::new();
+    let id = domain::events::EventId::new();
+    store.seed_processed_event(
+        &id,
+        "crashed",
+        false,
+        chrono::Utc::now().naive_utc() - chrono::Duration::seconds(HANDLER_LEASE_SECONDS + 1),
+    );
+    let nacks = Arc::new(Mutex::new(0));
+    let consumer = RedeliveringConsumer {
+        id: Some(id),
+        event: movie_discovered(),
+        times: 1,
+        nacks: Arc::clone(&nacks),
+    };
+
+    WorkerService::new(Arc::new(consumer), vec![handler], store)
+        .unwrap()
+        .run(tokio::sync::watch::channel(false).1)
+        .await;
+
+    assert_eq!(*calls.lock().unwrap(), 1);
+    assert_eq!(*nacks.lock().unwrap(), 0);
+}
+
+#[tokio::test]
+async fn a_failed_handler_releases_its_claim_so_redelivery_retries() {
+    let (handler, calls) = CountingHandler::new("flaky", 1);
+    let store = InMemoryStore::new();
+    let nacks = Arc::new(Mutex::new(0));
+    let consumer = RedeliveringConsumer {
+        id: Some(domain::events::EventId::new()),
+        event: movie_discovered(),
+        times: 3,
+        nacks: Arc::clone(&nacks),
+    };
+
+    WorkerService::new(Arc::new(consumer), vec![handler], store.clone())
+        .unwrap()
+        .run(tokio::sync::watch::channel(false).1)
+        .await;
+
+    // Delivery 1 fails and releases; 2 succeeds; 3 is skipped as done.
+    assert_eq!(*calls.lock().unwrap(), 2);
+    assert_eq!(*nacks.lock().unwrap(), 1);
+}