Stabilize abort task follow-up handling (#13874)

- production logic plus tests; cancel running tasks before clearing
pending turn state
- suppress follow-up model requests after cancellation and assert on
stabilized request counts instead of fixed sleeps

codex-rs/core/src/codex.rs

@@ -2702,8 +2702,9 @@ impl Session {
     /// Emit an exec approval request event and await the user's decision.
     ///
     /// The request is keyed by `call_id` + `approval_id` so matching responses
-    /// are delivered to the correct in-flight turn. If the task is aborted,
-    /// this returns the default `ReviewDecision` (`Denied`).
+    /// are delivered to the correct in-flight turn. If the pending approval is
+    /// cleared before a response arrives, treat it as an abort so interrupted
+    /// turns do not continue on a synthetic denial.
     ///
     /// Note that if `available_decisions` is `None`, then the other fields will
     /// be used to derive the available decisions via
@@ -2777,7 +2778,7 @@ impl Session {
             parsed_cmd,
         });
         self.send_event(turn_context, event).await;
-        rx_approve.await.unwrap_or_default()
+        rx_approve.await.unwrap_or(ReviewDecision::Abort)
     }
 
     pub async fn request_patch_approval(
@@ -6859,6 +6860,10 @@ async fn try_run_sampling_request(
 
     drain_in_flight(&mut in_flight, sess.clone(), turn_context.clone()).await?;
 
+    if cancellation_token.is_cancelled() {
+        return Err(CodexErr::TurnAborted);
+    }
+
     if should_emit_turn_diff {
         let unified_diff = {
             let mut tracker = turn_diff_tracker.lock().await;