Fail exec client operations after disconnect

Reject new exec-server operations once the transport disconnects and convert pending RPC calls into closed errors. This lets remote MCP stdio calls surface executor loss immediately instead of waiting for the MCP tool timeout.

Co-authored-by: Codex <noreply@openai.com>

Author: aibrahim-oai

codex-rs/exec-server/src/client.rs

@@ -127,6 +127,7 @@ struct Inner {
     // need serialization so concurrent register/remove operations do not
     // overwrite each other's copy-on-write updates.
     sessions_write_lock: Mutex<()>,
+    disconnected: std::sync::RwLock<Option<String>>,
     session_id: std::sync::RwLock<Option<String>>,
     reader_task: tokio::task::JoinHandle<()>,
 }
@@ -158,6 +159,8 @@ pub enum ExecServerError {
     InitializeTimedOut { timeout: Duration },
     #[error("exec-server transport closed")]
     Closed,
+    #[error("{0}")]
+    Disconnected(String),
     #[error("failed to serialize or deserialize exec-server JSON: {0}")]
     Json(#[from] serde_json::Error),
     #[error("exec-server protocol error: {0}")]
@@ -233,127 +236,85 @@ impl ExecServerClient {
     }
 
     pub async fn exec(&self, params: ExecParams) -> Result<ExecResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(EXEC_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(EXEC_METHOD, &params).await
     }
 
     pub async fn read(&self, params: ReadParams) -> Result<ReadResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(EXEC_READ_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(EXEC_READ_METHOD, &params).await
     }
 
     pub async fn write(
         &self,
         process_id: &ProcessId,
         chunk: Vec<u8>,
     ) -> Result<WriteResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(
-                EXEC_WRITE_METHOD,
-                &WriteParams {
-                    process_id: process_id.clone(),
-                    chunk: chunk.into(),
-                },
-            )
-            .await
-            .map_err(Into::into)
+        self.call(
+            EXEC_WRITE_METHOD,
+            &WriteParams {
+                process_id: process_id.clone(),
+                chunk: chunk.into(),
+            },
+        )
+        .await
     }
 
     pub async fn terminate(
         &self,
         process_id: &ProcessId,
     ) -> Result<TerminateResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(
-                EXEC_TERMINATE_METHOD,
-                &TerminateParams {
-                    process_id: process_id.clone(),
-                },
-            )
-            .await
-            .map_err(Into::into)
+        self.call(
+            EXEC_TERMINATE_METHOD,
+            &TerminateParams {
+                process_id: process_id.clone(),
+            },
+        )
+        .await
     }
 
     pub async fn fs_read_file(
         &self,
         params: FsReadFileParams,
     ) -> Result<FsReadFileResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(FS_READ_FILE_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(FS_READ_FILE_METHOD, &params).await
     }
 
     pub async fn fs_write_file(
         &self,
         params: FsWriteFileParams,
     ) -> Result<FsWriteFileResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(FS_WRITE_FILE_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(FS_WRITE_FILE_METHOD, &params).await
     }
 
     pub async fn fs_create_directory(
         &self,
         params: FsCreateDirectoryParams,
     ) -> Result<FsCreateDirectoryResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(FS_CREATE_DIRECTORY_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(FS_CREATE_DIRECTORY_METHOD, &params).await
     }
 
     pub async fn fs_get_metadata(
         &self,
         params: FsGetMetadataParams,
     ) -> Result<FsGetMetadataResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(FS_GET_METADATA_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(FS_GET_METADATA_METHOD, &params).await
     }
 
     pub async fn fs_read_directory(
         &self,
         params: FsReadDirectoryParams,
     ) -> Result<FsReadDirectoryResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(FS_READ_DIRECTORY_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(FS_READ_DIRECTORY_METHOD, &params).await
     }
 
     pub async fn fs_remove(
         &self,
         params: FsRemoveParams,
     ) -> Result<FsRemoveResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(FS_REMOVE_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(FS_REMOVE_METHOD, &params).await
     }
 
     pub async fn fs_copy(&self, params: FsCopyParams) -> Result<FsCopyResponse, ExecServerError> {
-        self.inner
-            .client
-            .call(FS_COPY_METHOD, &params)
-            .await
-            .map_err(Into::into)
+        self.call(FS_COPY_METHOD, &params).await
     }
 
     pub(crate) async fn register_session(
@@ -398,7 +359,7 @@ impl ExecServerClient {
                                 && let Err(err) =
                                     handle_server_notification(&inner, notification).await
                             {
-                                fail_all_sessions(
+                                mark_disconnected(
                                     &inner,
                                     format!("exec-server notification handling failed: {err}"),
                                 )
@@ -408,7 +369,7 @@ impl ExecServerClient {
                         }
                         RpcClientEvent::Disconnected { reason } => {
                             if let Some(inner) = weak.upgrade() {
-                                fail_all_sessions(&inner, disconnected_message(reason.as_deref()))
+                                mark_disconnected(&inner, disconnected_message(reason.as_deref()))
                                     .await;
                             }
                             return;
@@ -421,6 +382,7 @@ impl ExecServerClient {
                 client: rpc_client,
                 sessions: ArcSwap::from_pointee(HashMap::new()),
                 sessions_write_lock: Mutex::new(()),
+                disconnected: std::sync::RwLock::new(None),
                 session_id: std::sync::RwLock::new(None),
                 reader_task,
             }
@@ -438,6 +400,30 @@ impl ExecServerClient {
             .await
             .map_err(ExecServerError::Json)
     }
+
+    async fn call<P, T>(&self, method: &str, params: &P) -> Result<T, ExecServerError>
+    where
+        P: serde::Serialize,
+        T: serde::de::DeserializeOwned,
+    {
+        if let Some(error) = self.inner.disconnected_error() {
+            return Err(error);
+        }
+
+        match self.inner.client.call(method, params).await {
+            Ok(response) => Ok(response),
+            Err(error) => {
+                let error = ExecServerError::from(error);
+                if is_transport_closed_error(&error) {
+                    let message = disconnected_message(/*reason*/ None);
+                    let message = mark_disconnected(&self.inner, message).await;
+                    Err(ExecServerError::Disconnected(message))
+                } else {
+                    Err(error)
+                }
+            }
+        }
+    }
 }
 
 impl From<RpcCallError> for ExecServerError {
@@ -573,6 +559,26 @@ impl Session {
 }
 
 impl Inner {
+    fn disconnected_error(&self) -> Option<ExecServerError> {
+        self.disconnected
+            .read()
+            .unwrap_or_else(std::sync::PoisonError::into_inner)
+            .clone()
+            .map(ExecServerError::Disconnected)
+    }
+
+    fn set_disconnected(&self, message: String) -> Option<String> {
+        let mut disconnected = self
+            .disconnected
+            .write()
+            .unwrap_or_else(std::sync::PoisonError::into_inner);
+        if disconnected.is_some() {
+            return None;
+        }
+        *disconnected = Some(message.clone());
+        Some(message)
+    }
+
     fn get_session(&self, process_id: &ProcessId) -> Option<Arc<SessionState>> {
         self.sessions.load().get(process_id).cloned()
     }
@@ -583,6 +589,9 @@ impl Inner {
         session: Arc<SessionState>,
     ) -> Result<(), ExecServerError> {
         let _sessions_write_guard = self.sessions_write_lock.lock().await;
+        if let Some(error) = self.disconnected_error() {
+            return Err(error);
+        }
         let sessions = self.sessions.load();
         if sessions.contains_key(process_id) {
             return Err(ExecServerError::Protocol(format!(
@@ -623,14 +632,30 @@ fn disconnected_message(reason: Option<&str>) -> String {
 }
 
 fn is_transport_closed_error(error: &ExecServerError) -> bool {
-    matches!(error, ExecServerError::Closed)
-        || matches!(
-            error,
-            ExecServerError::Server {
-                code: -32000,
-                message,
-            } if message == "JSON-RPC transport closed"
-        )
+    matches!(
+        error,
+        ExecServerError::Closed | ExecServerError::Disconnected(_)
+    ) || matches!(
+        error,
+        ExecServerError::Server {
+            code: -32000,
+            message,
+        } if message == "JSON-RPC transport closed"
+    )
+}
+
+async fn mark_disconnected(inner: &Arc<Inner>, message: String) -> String {
+    if let Some(message) = inner.set_disconnected(message.clone()) {
+        fail_all_sessions(inner, message.clone()).await;
+        message
+    } else {
+        inner
+            .disconnected
+            .read()
+            .unwrap_or_else(std::sync::PoisonError::into_inner)
+            .clone()
+            .unwrap_or(message)
+    }
 }
 
 async fn fail_all_sessions(inner: &Arc<Inner>, message: String) {