From a6f0fc0c0f59e05faf1b8621cec9fb6d97e31ca8 Mon Sep 17 00:00:00 2001
From: Larry
 <8cf5a83f590ec0955b11647d1c88f796a98e088c30a492c58e0e46c3026ae7a4@buzz.block.builderlab.xyz>
Date: Tue, 11 Aug 2026 12:38:21 -0400
Subject: [PATCH] fix(acp): release prepared edits before fallback

Signed-off-by: Larry <8cf5a83f590ec0955b11647d1c88f796a98e088c30a492c58e0e46c3026ae7a4@buzz.block.builderlab.xyz>
---
 crates/buzz-acp/src/lib.rs   |  6 +++-
 crates/buzz-acp/src/queue.rs | 65 ++++++++++++++++++++++++++++--------
 2 files changed, 56 insertions(+), 15 deletions(-)

diff --git a/crates/buzz-acp/src/lib.rs b/crates/buzz-acp/src/lib.rs
index 1e03b8cc0..122da7165 100644
--- a/crates/buzz-acp/src/lib.rs
+++ b/crates/buzz-acp/src/lib.rs
@@ -2627,9 +2627,13 @@ async fn tokio_main() -> Result<()> {
                                         if queue.has_native_steer_reservations(
                                             buzz_event.channel_id,
                                         ) {
+                                            let released = queue.release_native_steers(
+                                                buzz_event.channel_id,
+                                            );
                                             tracing::debug!(
                                                 channel_id = %buzz_event.channel_id,
-                                                "native steer preparation already pending; preserving channel order via cancel+merge"
+                                                released,
+                                                "native steer preparation already pending; releasing reservations for ordered cancel+merge"
                                             );
                                             false
                                         } else if is_edit
diff --git a/crates/buzz-acp/src/queue.rs b/crates/buzz-acp/src/queue.rs
index 84c77bc24..3d03b6086 100644
--- a/crates/buzz-acp/src/queue.rs
+++ b/crates/buzz-acp/src/queue.rs
@@ -796,6 +796,29 @@ impl EventQueue {
         }
     }
 
+    /// Release every native-steer reservation for `channel_id` to the queue
+    /// front, preserving original FIFO order. Detached edit preparation then
+    /// observes its missing reservation and discards the stale completion.
+    pub fn release_native_steers(&mut self, channel_id: Uuid) -> usize {
+        let Some(entries) = self.withheld_native_steer.remove(&channel_id) else {
+            return 0;
+        };
+        let n = entries.len();
+        let queue = self.queues.entry(channel_id).or_default();
+        for qe in entries.into_iter().rev() {
+            queue.push_front(qe);
+        }
+        while queue.len() > MAX_PENDING_PER_CHANNEL {
+            queue.pop_back();
+            tracing::warn!(
+                channel_id = %channel_id,
+                limit = MAX_PENDING_PER_CHANNEL,
+                "withheld-steer release overflow — dropped newest event to enforce cap"
+            );
+        }
+        n
+    }
+
     /// Bulk-release every withheld event for `channel_id` back to the queue
     /// front, preserving relative FIFO order.
     ///
@@ -810,21 +833,9 @@ impl EventQueue {
     /// composes to original-FIFO order at the queue front (same discipline
     /// as `requeue_preserve_timestamps` at line 453).
     fn recover_withheld_for_expired_channel(&mut self, channel_id: Uuid) {
-        let Some(entries) = self.withheld_native_steer.remove(&channel_id) else {
+        let n = self.release_native_steers(channel_id);
+        if n == 0 {
             return;
-        };
-        let n = entries.len();
-        let queue = self.queues.entry(channel_id).or_default();
-        for qe in entries.into_iter().rev() {
-            queue.push_front(qe);
-        }
-        while queue.len() > MAX_PENDING_PER_CHANNEL {
-            queue.pop_back();
-            tracing::warn!(
-                channel_id = %channel_id,
-                limit = MAX_PENDING_PER_CHANNEL,
-                "withheld-steer recovery overflow — dropped newest event to enforce cap"
-            );
         }
         tracing::warn!(
             channel_id = %channel_id,
@@ -4758,6 +4769,32 @@ mod tests {
         ));
     }
 
+    #[test]
+    fn releasing_pending_preparation_restores_fifo_ahead_of_later_event() {
+        let mut q = EventQueue::new(DedupMode::Queue);
+        let ch = Uuid::new_v4();
+        let edit = make_queued_at(ch, "edit", Duration::from_millis(20));
+        let edit_id = edit.event.id.to_hex();
+        let later = make_queued_at(ch, "later", Duration::from_millis(10));
+        let later_id = later.event.id.to_hex();
+        q.push(edit);
+        assert!(q.mark_native_steer_pending(ch, &edit_id));
+        q.push(later);
+
+        // A later event triggers cancel+merge. Releasing the pending edit first
+        // makes both events visible to the next flush in original arrival order;
+        // the detached preparation will be stale because its reservation is gone.
+        assert_eq!(q.release_native_steers(ch), 1);
+        assert!(!q.has_native_steer_reservation(ch, &edit_id));
+        let replacement = q.flush_next().expect("both events should dispatch");
+        let ids: Vec<_> = replacement
+            .events
+            .iter()
+            .map(|event| event.event.id.to_hex())
+            .collect();
+        assert_eq!(ids, vec![edit_id, later_id]);
+    }
+
     /// Bulk-release on expiry must preserve original FIFO. The
     /// implementation iterates the side-table entries in reverse and
     /// `push_front`s each — composing to original-FIFO at the queue front.