fix: introduce EventMsg::TurnAborted (#2365)

Introduces `EventMsg::TurnAborted` that should be sent in response to
`Op::Interrupt`.

In the MCP server, updates the handling of a
`ClientRequest::InterruptConversation` request such that it sends the
`Op::Interrupt` but does not respond to the request until it sees an
`EventMsg::TurnAborted`.

codex-rs/core/src/codex.rs

@@ -14,6 +14,8 @@ use codex_apply_patch::ApplyPatchAction;
 use codex_apply_patch::MaybeApplyPatchVerified;
 use codex_apply_patch::maybe_parse_apply_patch_verified;
 use codex_login::CodexAuth;
+use codex_protocol::protocol::TurnAbortReason;
+use codex_protocol::protocol::TurnAbortedEvent;
 use futures::prelude::*;
 use mcp_types::CallToolResult;
 use serde::Serialize;
@@ -535,7 +537,7 @@ impl Session {
     pub fn set_task(&self, task: AgentTask) {
         let mut state = self.state.lock_unchecked();
         if let Some(current_task) = state.current_task.take() {
-            current_task.abort();
+            current_task.abort(TurnAbortReason::Replaced);
         }
         state.current_task = Some(task);
     }
@@ -852,13 +854,13 @@ impl Session {
             .await
     }
 
-    fn abort(&self) {
-        info!("Aborting existing session");
+    fn interrupt_task(&self) {
+        info!("interrupt received: abort current task, if any");
         let mut state = self.state.lock_unchecked();
         state.pending_approvals.clear();
         state.pending_input.clear();
         if let Some(task) = state.current_task.take() {
-            task.abort();
+            task.abort(TurnAbortReason::Interrupted);
         }
     }
 
@@ -894,7 +896,7 @@ impl Session {
 
 impl Drop for Session {
     fn drop(&mut self) {
-        self.abort();
+        self.interrupt_task();
     }
 }
 
@@ -964,14 +966,13 @@ impl AgentTask {
         }
     }
 
-    fn abort(self) {
+    fn abort(self, reason: TurnAbortReason) {
+        // TOCTOU?
         if !self.handle.is_finished() {
             self.handle.abort();
             let event = Event {
                 id: self.sub_id,
-                msg: EventMsg::Error(ErrorEvent {
-                    message: " Turn interrupted".to_string(),
-                }),
+                msg: EventMsg::TurnAborted(TurnAbortedEvent { reason }),
             };
             let tx_event = self.sess.tx_event.clone();
             tokio::spawn(async move {
@@ -994,7 +995,7 @@ async fn submission_loop(
         debug!(?sub, "Submission");
         match sub.op {
             Op::Interrupt => {
-                sess.abort();
+                sess.interrupt_task();
             }
             Op::UserInput { items } => {
                 // attempt to inject input into current task
@@ -1065,13 +1066,13 @@ async fn submission_loop(
             }
             Op::ExecApproval { id, decision } => match decision {
                 ReviewDecision::Abort => {
-                    sess.abort();
+                    sess.interrupt_task();
                 }
                 other => sess.notify_approval(&id, other),
             },
             Op::PatchApproval { id, decision } => match decision {
                 ReviewDecision::Abort => {
-                    sess.abort();
+                    sess.interrupt_task();
                 }
                 other => sess.notify_approval(&id, other),
             },