Fix hang on turn/interrupt (#18392)

Fix a bug where the `turn/interrupt` RPC hangs when interrupting a turn
that has already completed.

Before this change, `turn/interrupt` requests were queued in app-server
and only answered when a later TurnAborted event arrived. If the target
turn was already complete, core treated Op::Interrupt as a no-op, so no
abort event was emitted and the RPC could hang indefinitely.

This change fixes that in two places:

* Reject turn/interrupt immediately with `INVALID_REQUEST` when the
requested turn is no longer the active turn.
* Resolve any already-accepted pending interrupt requests when the turn
reaches TurnComplete, covering the case where a turn finishes naturally
after the interrupt request is accepted but before it aborts.

I tested this by adding a failing test in
707487c063. You may view the results here:
https://github.com/openai/codex/actions/runs/24585182419/

<img width="1512" height="310" alt="CleanShot 2026-04-17 at 16 33 30@2x"
src="https://github.com/user-attachments/assets/f4a88228-b2a4-41f4-9aaa-ec82814096af"
/>

codex-rs/app-server/src/thread_state.rs

@@ -60,6 +60,7 @@ pub(crate) struct ThreadState {
     pub(crate) pending_interrupts: PendingInterruptQueue,
     pub(crate) pending_rollbacks: Option<ConnectionRequestId>,
     pub(crate) turn_summary: TurnSummary,
+    pub(crate) last_terminal_turn_id: Option<String>,
     pub(crate) cancel_tx: Option<oneshot::Sender<()>>,
     pub(crate) experimental_raw_events: bool,
     pub(crate) listener_generation: u64,
@@ -114,7 +115,7 @@ impl ThreadState {
         self.current_turn_history.active_turn_snapshot()
     }
 
-    pub(crate) fn track_current_turn_event(&mut self, event: &EventMsg) {
+    pub(crate) fn track_current_turn_event(&mut self, event_turn_id: &str, event: &EventMsg) {
         if let EventMsg::TurnStarted(payload) = event {
             self.turn_summary.started_at = payload.started_at;
         }
@@ -122,6 +123,7 @@ impl ThreadState {
         if matches!(event, EventMsg::TurnAborted(_) | EventMsg::TurnComplete(_))
             && !self.current_turn_history.has_active_turn()
         {
+            self.last_terminal_turn_id = Some(event_turn_id.to_string());
             self.current_turn_history.reset();
         }
     }