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) {
+    fn interrupt_task(&self) {
-        info!("Aborting existing session");
+        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 {
+                msg: EventMsg::TurnAborted(TurnAbortedEvent { reason }),
-                    message: " Turn interrupted".to_string(),
-                }),
             };
             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),
             },

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -21,6 +21,7 @@ use codex_core::protocol::PatchApplyBeginEvent;
 use codex_core::protocol::PatchApplyEndEvent;
 use codex_core::protocol::SessionConfiguredEvent;
 use codex_core::protocol::TaskCompleteEvent;
+use codex_core::protocol::TurnAbortReason;
 use codex_core::protocol::TurnDiffEvent;
 use owo_colors::OwoColorize;
 use owo_colors::Style;
@@ -522,6 +523,14 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             EventMsg::GetHistoryEntryResponse(_) => {
                 // Currently ignored in exec output.
             }
+            EventMsg::TurnAborted(abort_reason) => match abort_reason.reason {
+                TurnAbortReason::Interrupted => {
+                    ts_println!(self, "task interrupted");
+                }
+                TurnAbortReason::Replaced => {
+                    ts_println!(self, "task aborted: replaced by a new task");
+                }
+            },
             EventMsg::ShutdownComplete => return CodexStatus::Shutdown,
         }
         CodexStatus::Running

codex-rs/mcp-server/src/codex_message_processor.rs

@@ -77,6 +77,8 @@ pub(crate) struct CodexMessageProcessor {
     codex_linux_sandbox_exe: Option<PathBuf>,
     conversation_listeners: HashMap<Uuid, oneshot::Sender<()>>,
     active_login: Arc<Mutex<Option<ActiveLogin>>>,
+    // Queue of pending interrupt requests per conversation. We reply when TurnAborted arrives.
+    pending_interrupts: Arc<Mutex<HashMap<Uuid, Vec<RequestId>>>>,
 }
 
 impl CodexMessageProcessor {
@@ -91,6 +93,7 @@ impl CodexMessageProcessor {
             codex_linux_sandbox_exe,
             conversation_listeners: HashMap::new(),
             active_login: Arc::new(Mutex::new(None)),
+            pending_interrupts: Arc::new(Mutex::new(HashMap::new())),
         }
     }
 
@@ -399,13 +402,14 @@ impl CodexMessageProcessor {
             return;
         };
 
-        let _ = conversation.submit(Op::Interrupt).await;
+        // Record the pending interrupt so we can reply when TurnAborted arrives.
+        {
+            let mut map = self.pending_interrupts.lock().await;
+            map.entry(conversation_id.0).or_default().push(request_id);
+        }
 
-        // Apparently CodexConversation does not send an ack for Op::Interrupt,
+        // Submit the interrupt; we'll respond upon TurnAborted.
-        // so we can reply to the request right away.
+        let _ = conversation.submit(Op::Interrupt).await;
-        self.outgoing
-            .send_response(request_id, InterruptConversationResponse {})
-            .await;
     }
 
     async fn add_conversation_listener(
@@ -433,6 +437,7 @@ impl CodexMessageProcessor {
         self.conversation_listeners
             .insert(subscription_id, cancel_tx);
         let outgoing_for_task = self.outgoing.clone();
+        let pending_interrupts = self.pending_interrupts.clone();
         tokio::spawn(async move {
             loop {
                 tokio::select! {
@@ -473,7 +478,7 @@ impl CodexMessageProcessor {
                         })
                         .await;
 
-                        apply_bespoke_event_handling(event, conversation_id, conversation.clone(), outgoing_for_task.clone()).await;
+                        apply_bespoke_event_handling(event.clone(), conversation_id, conversation.clone(), outgoing_for_task.clone(), pending_interrupts.clone()).await;
                     }
                 }
             }
@@ -512,6 +517,7 @@ async fn apply_bespoke_event_handling(
     conversation_id: ConversationId,
     conversation: Arc<CodexConversation>,
     outgoing: Arc<OutgoingMessageSender>,
+    pending_interrupts: Arc<Mutex<HashMap<Uuid, Vec<RequestId>>>>,
 ) {
     let Event { id: event_id, msg } = event;
     match msg {
@@ -560,6 +566,22 @@ async fn apply_bespoke_event_handling(
                 on_exec_approval_response(event_id, rx, conversation).await;
             });
         }
+        // If this is a TurnAborted, reply to any pending interrupt requests.
+        EventMsg::TurnAborted(turn_aborted_event) => {
+            let pending = {
+                let mut map = pending_interrupts.lock().await;
+                map.remove(&conversation_id.0).unwrap_or_default()
+            };
+            if !pending.is_empty() {
+                let response = InterruptConversationResponse {
+                    abort_reason: turn_aborted_event.reason,
+                };
+                for rid in pending {
+                    outgoing.send_response(rid, response.clone()).await;
+                }
+            }
+        }
+
         _ => {}
     }
 }

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -272,6 +272,7 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::TurnDiff(_)
                     | EventMsg::GetHistoryEntryResponse(_)
                     | EventMsg::PlanUpdate(_)
+                    | EventMsg::TurnAborted(_)
                     | EventMsg::ShutdownComplete => {
                         // For now, we do not do anything extra for these
                         // events. Note that

codex-rs/mcp-server/src/conversation_loop.rs

@@ -52,7 +52,6 @@ pub async fn run_conversation_loop(
                             call_id,
                         )
                         .await;
-                        continue;
                     }
                     EventMsg::Error(_) => {
                         error!("Codex runtime error");
@@ -75,7 +74,6 @@ pub async fn run_conversation_loop(
                             event.id.clone(),
                         )
                         .await;
-                        continue;
                     }
                     EventMsg::TaskComplete(_) => {}
                     EventMsg::SessionConfigured(_) => {
@@ -107,6 +105,7 @@ pub async fn run_conversation_loop(
                     | EventMsg::PatchApplyEnd(_)
                     | EventMsg::GetHistoryEntryResponse(_)
                     | EventMsg::PlanUpdate(_)
+                    | EventMsg::TurnAborted(_)
                     | EventMsg::ShutdownComplete => {
                         // For now, we do not do anything extra for these
                         // events. Note that

codex-rs/mcp-server/src/wire_format.rs

@@ -6,6 +6,7 @@ use codex_core::protocol::AskForApproval;
 use codex_core::protocol::FileChange;
 use codex_core::protocol::ReviewDecision;
 use codex_core::protocol::SandboxPolicy;
+use codex_core::protocol::TurnAbortReason;
 use codex_core::protocol_config_types::ReasoningEffort;
 use codex_core::protocol_config_types::ReasoningSummary;
 use mcp_types::RequestId;
@@ -191,9 +192,11 @@ pub struct InterruptConversationParams {
     pub conversation_id: ConversationId,
 }
 
-#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+#[derive(Serialize, Deserialize, Debug, Clone)]
 #[serde(rename_all = "camelCase")]
-pub struct InterruptConversationResponse {}
+pub struct InterruptConversationResponse {
+    pub abort_reason: TurnAbortReason,
+}
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
 #[serde(rename_all = "camelCase")]

codex-rs/mcp-server/tests/interrupt.rs

@@ -5,8 +5,6 @@ use std::path::Path;
 
 use codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR;
 use codex_mcp_server::CodexToolCallParam;
-use mcp_types::JSONRPCResponse;
-use mcp_types::RequestId;
 use serde_json::json;
 use tempfile::TempDir;
 use tokio::time::timeout;
@@ -100,22 +98,13 @@ async fn shell_command_interruption() -> anyhow::Result<()> {
         )
         .await?;
 
-    // Expect Codex to return an error or interruption response
+    // Expect Codex to emit a TurnAborted event notification
-    let codex_response: JSONRPCResponse = timeout(
+    let _turn_aborted = timeout(
         DEFAULT_READ_TIMEOUT,
-        mcp_process.read_stream_until_response_message(RequestId::Integer(codex_request_id)),
+        mcp_process.read_stream_until_notification_message("turn_aborted"),
     )
     .await??;
 
-    assert!(
-        codex_response
-            .result
-            .as_object()
-            .map(|o| o.contains_key("error"))
-            .unwrap_or(false),
-        "Expected an interruption or error result, got: {codex_response:?}"
-    );
-
     let codex_reply_request_id = mcp_process
         .send_codex_reply_tool_call(&session_id, "Second Run: run `sleep 60`")
         .await?;
@@ -131,21 +120,12 @@ async fn shell_command_interruption() -> anyhow::Result<()> {
         )
         .await?;
 
-    // Expect Codex to return an error or interruption response
+    // Expect Codex to emit a TurnAborted event notification
-    let codex_response: JSONRPCResponse = timeout(
+    let _turn_aborted = timeout(
         DEFAULT_READ_TIMEOUT,
-        mcp_process.read_stream_until_response_message(RequestId::Integer(codex_reply_request_id)),
+        mcp_process.read_stream_until_notification_message("turn_aborted"),
     )
     .await??;
-
-    assert!(
-        codex_response
-            .result
-            .as_object()
-            .map(|o| o.contains_key("error"))
-            .unwrap_or(false),
-        "Expected an interruption or error result, got: {codex_response:?}"
-    );
     Ok(())
 }
 

codex-rs/protocol/src/protocol.rs

@@ -39,7 +39,7 @@ pub struct Submission {
 #[non_exhaustive]
 pub enum Op {
     /// Abort current task.
-    /// This server sends no corresponding Event
+    /// This server sends [`EventMsg::TurnAborted`] in response.
     Interrupt,
 
     /// Input from the user
@@ -422,6 +422,8 @@ pub enum EventMsg {
 
     PlanUpdate(UpdatePlanArgs),
 
+    TurnAborted(TurnAbortedEvent),
+
     /// Notification that the agent is shutting down.
     ShutdownComplete,
 }
@@ -745,6 +747,18 @@ pub struct Chunk {
     pub inserted_lines: Vec<String>,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct TurnAbortedEvent {
+    pub reason: TurnAbortReason,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum TurnAbortReason {
+    Interrupted,
+    Replaced,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

codex-rs/tui/src/chatwidget.rs

@@ -635,6 +635,7 @@ impl ChatWidget<'_> {
             EventMsg::TaskComplete(TaskCompleteEvent { .. }) => self.on_task_complete(),
             EventMsg::TokenCount(token_usage) => self.on_token_count(token_usage),
             EventMsg::Error(ErrorEvent { message }) => self.on_error(message),
+            EventMsg::TurnAborted(_) => self.on_error("Turn interrupted".to_owned()),
             EventMsg::PlanUpdate(update) => self.on_plan_update(update),
             EventMsg::ExecApprovalRequest(ev) => self.on_exec_approval_request(id, ev),
             EventMsg::ApplyPatchApprovalRequest(ev) => self.on_apply_patch_approval_request(id, ev),