fix(acp): discard stale prepared edit steers

Signed-off-by: Larry <8cf5a83f590ec0955b11647d1c88f796a98e088c30a492c58e0e46c3026ae7a4@buzz.block.builderlab.xyz>

crates/buzz-acp/src/lib.rs

@@ -1389,6 +1389,13 @@ struct NativeSteerPrepared {
     prompt_blocks: Vec<String>,
 }
 
+/// Async edit enrichment may finish after channel membership was revoked.
+/// Such prepared work is stale: removal drains its queue reservation, and it
+/// must never be forwarded to an otherwise still-live ACP turn.
+fn native_steer_preparation_is_stale(removed_channels: &HashSet<Uuid>, channel_id: Uuid) -> bool {
+    removed_channels.contains(&channel_id)
+}
+
 struct SteerAckEvent {
     channel_id: Uuid,
     event_id: String,
@@ -2792,6 +2799,14 @@ async fn tokio_main() -> Result<()> {
                 event,
                 prompt_blocks,
             })) => {
+                if native_steer_preparation_is_stale(&removed_channels, channel_id) {
+                    tracing::debug!(
+                        %channel_id,
+                        event_id = %event.id.to_hex(),
+                        "discarding native steer prepared after channel removal"
+                    );
+                    continue;
+                }
                 if !try_native_steer(
                     &mut pool,
                     &mut queue,

crates/buzz-acp/src/queue.rs

@@ -5099,6 +5099,37 @@ mod tests {
         assert_eq!(batch.events[0].event.id.to_hex(), event_id);
     }
 
+    #[test]
+    fn removed_channel_discards_late_async_edit_steer_preparation() {
+        let mut q = EventQueue::new(DedupMode::Queue);
+        let ch = Uuid::new_v4();
+        let event = edit_event(&"ab".repeat(32));
+        let event_id = event.id.to_hex();
+        q.push(QueuedEvent {
+            channel_id: ch,
+            event,
+            received_at: Instant::now(),
+            prompt_tag: "@mention".into(),
+        });
+        q.in_flight_channels.insert(ch);
+        q.in_flight_deadlines
+            .insert(ch, Instant::now() + Duration::from_secs(60));
+
+        assert!(q.mark_native_steer_pending(ch, &event_id));
+        q.drain_channel(ch);
+        let removed_channels = HashSet::from([ch]);
+        assert!(crate::native_steer_preparation_is_stale(
+            &removed_channels,
+            ch
+        ));
+
+        // A late preparation is discarded by the main loop. Its reservation
+        // was already drained, so release cannot resurrect stale work.
+        q.release_native_steer(ch, &event_id);
+        q.mark_complete(ch);
+        assert!(q.flush_next().is_none());
+    }
+
     #[test]
     fn native_steer_edit_uses_original_thread_anchor() {
         let original_id = "66".repeat(32);