[codex] Handle Ctrl-C for non-TTY unified exec (#26734)

## Why

A long-running unified exec process started with `tty: false` could not
be interrupted via `write_stdin`: ordinary non-TTY stdin writes are
rejected once stdin is closed, but an exact U+0003 payload should still
map to a process interrupt. The interrupt should flow through the same
process lifecycle path as a real signal so Codex preserves
process-reported output and exit metadata instead of fabricating a
Ctrl-C exit code or tearing down the session early.

## What Changed

- Add `process/signal` to exec-server with `ProcessSignal::Interrupt`
and an empty response.
- Add a non-consuming `ProcessHandle::signal` path for spawned
processes; on Unix it sends SIGINT to the process group and leaves
terminate/hard-kill unchanged.
- Route non-TTY U+0003 `write_stdin` through `process.signal(...)`
instead of `terminate`, then let the normal post-write collection path
drain output and observe exit.
- Add exec-server coverage where a shell `trap INT` handler prints the
signal and exits with its own code.
- Add unified exec coverage where a `tty: false` process traps SIGINT,
emits output, and exits with its own code.

## Validation

- `just test -p codex-exec-server
exec_process_signal_interrupts_process`
- `just test -p codex-exec-server`
- `just test -p codex-core
write_stdin_ctrl_c_interrupts_non_tty_session`

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

@@ -35,6 +35,7 @@ use crate::protocol::EXEC_EXITED_METHOD;
 use crate::protocol::EXEC_METHOD;
 use crate::protocol::EXEC_OUTPUT_DELTA_METHOD;
 use crate::protocol::EXEC_READ_METHOD;
+use crate::protocol::EXEC_SIGNAL_METHOD;
 use crate::protocol::EXEC_TERMINATE_METHOD;
 use crate::protocol::EXEC_WRITE_METHOD;
 use crate::protocol::EnvironmentInfo;
@@ -80,8 +81,11 @@ use crate::protocol::INITIALIZED_METHOD;
 use crate::protocol::InitializeParams;
 use crate::protocol::InitializeResponse;
 use crate::protocol::ProcessOutputChunk;
+use crate::protocol::ProcessSignal;
 use crate::protocol::ReadParams;
 use crate::protocol::ReadResponse;
+use crate::protocol::SignalParams;
+use crate::protocol::SignalResponse;
 use crate::protocol::TerminateParams;
 use crate::protocol::TerminateResponse;
 use crate::protocol::WriteParams;
@@ -394,6 +398,23 @@ impl ExecServerClient {
         .await
     }
 
+    pub async fn signal(
+        &self,
+        process_id: &ProcessId,
+        signal: ProcessSignal,
+    ) -> Result<(), ExecServerError> {
+        let _response: SignalResponse = self
+            .call(
+                EXEC_SIGNAL_METHOD,
+                &SignalParams {
+                    process_id: process_id.clone(),
+                    signal,
+                },
+            )
+            .await?;
+        Ok(())
+    }
+
     pub async fn terminate(
         &self,
         process_id: &ProcessId,
@@ -763,6 +784,10 @@ impl Session {
         self.client.write(&self.process_id, chunk).await
     }
 
+    pub(crate) async fn signal(&self, signal: ProcessSignal) -> Result<(), ExecServerError> {
+        self.client.signal(&self.process_id, signal).await
+    }
+
     pub(crate) async fn terminate(&self) -> Result<(), ExecServerError> {
         self.client.terminate(&self.process_id).await?;
         Ok(())

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

@@ -93,9 +93,12 @@ pub use protocol::HttpRequestResponse;
 pub use protocol::InitializeParams;
 pub use protocol::InitializeResponse;
 pub use protocol::ProcessOutputChunk;
+pub use protocol::ProcessSignal;
 pub use protocol::ReadParams;
 pub use protocol::ReadResponse;
 pub use protocol::ShellInfo;
+pub use protocol::SignalParams;
+pub use protocol::SignalResponse;
 pub use protocol::TerminateParams;
 pub use protocol::TerminateResponse;
 pub use protocol::WriteParams;

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

@@ -10,6 +10,7 @@ use codex_protocol::config_types::EnvironmentVariablePattern;
 use codex_protocol::config_types::ShellEnvironmentPolicy;
 use codex_protocol::shell_environment;
 use codex_utils_pty::ExecCommandSession;
+use codex_utils_pty::ProcessSignal as PtyProcessSignal;
 use codex_utils_pty::TerminalSize;
 use tokio::sync::Mutex;
 use tokio::sync::Notify;
@@ -33,8 +34,11 @@ use crate::protocol::ExecOutputStream;
 use crate::protocol::ExecParams;
 use crate::protocol::ExecResponse;
 use crate::protocol::ProcessOutputChunk;
+use crate::protocol::ProcessSignal;
 use crate::protocol::ReadParams;
 use crate::protocol::ReadResponse;
+use crate::protocol::SignalParams;
+use crate::protocol::SignalResponse;
 use crate::protocol::TerminateParams;
 use crate::protocol::TerminateResponse;
 use crate::protocol::WriteParams;
@@ -272,7 +276,6 @@ impl LocalProcess {
         &self,
         params: ReadParams,
     ) -> Result<ReadResponse, JSONRPCErrorError> {
-        let _process_id = params.process_id.clone();
         let after_seq = params.after_seq.unwrap_or(0);
         let max_bytes = params.max_bytes.unwrap_or(usize::MAX);
         let wait = Duration::from_millis(params.wait_ms.unwrap_or(0));
@@ -351,7 +354,6 @@ impl LocalProcess {
         &self,
         params: WriteParams,
     ) -> Result<WriteResponse, JSONRPCErrorError> {
-        let _process_id = params.process_id.clone();
         let _input_bytes = params.chunk.0.len();
         let writer_tx = {
             let process_map = self.inner.processes.lock().await;
@@ -383,11 +385,33 @@ impl LocalProcess {
         })
     }
 
+    pub(crate) async fn signal_process(
+        &self,
+        params: SignalParams,
+    ) -> Result<SignalResponse, JSONRPCErrorError> {
+        {
+            let process_map = self.inner.processes.lock().await;
+            match process_map.get(&params.process_id) {
+                Some(ProcessEntry::Running(process)) => {
+                    if process.exit_code.is_some() {
+                        return Ok(SignalResponse {});
+                    }
+                    process
+                        .session
+                        .signal(pty_process_signal(params.signal))
+                        .map_err(|err| internal_error(format!("failed to signal process: {err}")))?
+                }
+                Some(ProcessEntry::Starting) | None => {}
+            }
+        }
+
+        Ok(SignalResponse {})
+    }
+
     pub(crate) async fn terminate_process(
         &self,
         params: TerminateParams,
     ) -> Result<TerminateResponse, JSONRPCErrorError> {
-        let _process_id = params.process_id.clone();
         let running = {
             let process_map = self.inner.processes.lock().await;
             match process_map.get(&params.process_id) {
@@ -483,6 +507,10 @@ impl ExecProcess for LocalExecProcess {
         self.backend.write(&self.process_id, chunk).await
     }
 
+    async fn signal(&self, signal: ProcessSignal) -> Result<(), ExecServerError> {
+        self.backend.signal(&self.process_id, signal).await
+    }
+
     async fn terminate(&self) -> Result<(), ExecServerError> {
         self.backend.terminate(&self.process_id).await
     }
@@ -519,6 +547,20 @@ impl LocalProcess {
         .map_err(map_handler_error)
     }
 
+    async fn signal(
+        &self,
+        process_id: &ProcessId,
+        signal: ProcessSignal,
+    ) -> Result<(), ExecServerError> {
+        self.signal_process(SignalParams {
+            process_id: process_id.clone(),
+            signal,
+        })
+        .await
+        .map_err(map_handler_error)?;
+        Ok(())
+    }
+
     async fn terminate(&self, process_id: &ProcessId) -> Result<(), ExecServerError> {
         self.terminate_process(TerminateParams {
             process_id: process_id.clone(),
@@ -529,6 +571,12 @@ impl LocalProcess {
     }
 }
 
+fn pty_process_signal(signal: ProcessSignal) -> PtyProcessSignal {
+    match signal {
+        ProcessSignal::Interrupt => PtyProcessSignal::Interrupt,
+    }
+}
+
 fn map_handler_error(error: JSONRPCErrorError) -> ExecServerError {
     ExecServerError::Server {
         code: error.code,

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

@@ -10,6 +10,7 @@ use crate::ExecServerError;
 use crate::ProcessId;
 use crate::protocol::ExecParams;
 use crate::protocol::ProcessOutputChunk;
+use crate::protocol::ProcessSignal;
 use crate::protocol::ReadResponse;
 use crate::protocol::WriteResponse;
 
@@ -178,6 +179,8 @@ pub trait ExecProcess: Send + Sync {
 
     async fn write(&self, chunk: Vec<u8>) -> Result<WriteResponse, ExecServerError>;
 
+    async fn signal(&self, signal: ProcessSignal) -> Result<(), ExecServerError>;
+
     async fn terminate(&self) -> Result<(), ExecServerError>;
 }
 

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

@@ -15,6 +15,7 @@ pub const INITIALIZED_METHOD: &str = "initialized";
 pub const EXEC_METHOD: &str = "process/start";
 pub const EXEC_READ_METHOD: &str = "process/read";
 pub const EXEC_WRITE_METHOD: &str = "process/write";
+pub const EXEC_SIGNAL_METHOD: &str = "process/signal";
 pub const EXEC_TERMINATE_METHOD: &str = "process/terminate";
 pub const EXEC_OUTPUT_DELTA_METHOD: &str = "process/output";
 pub const EXEC_EXITED_METHOD: &str = "process/exited";
@@ -166,6 +167,23 @@ pub struct WriteResponse {
     pub status: WriteStatus,
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum ProcessSignal {
+    Interrupt,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SignalParams {
+    pub process_id: ProcessId,
+    pub signal: ProcessSignal,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SignalResponse {}
+
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct TerminateParams {

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

@@ -12,6 +12,7 @@ use crate::StartedExecProcess;
 use crate::client::LazyRemoteExecServerClient;
 use crate::client::Session;
 use crate::protocol::ExecParams;
+use crate::protocol::ProcessSignal;
 use crate::protocol::ReadResponse;
 use crate::protocol::WriteResponse;
 
@@ -76,6 +77,11 @@ impl ExecProcess for RemoteExecProcess {
         self.session.write(chunk).await
     }
 
+    async fn signal(&self, signal: ProcessSignal) -> Result<(), ExecServerError> {
+        trace!("exec process signal");
+        self.session.signal(signal).await
+    }
+
     async fn terminate(&self) -> Result<(), ExecServerError> {
         trace!("exec process terminate");
         self.session.terminate().await

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

@@ -42,6 +42,8 @@ use crate::protocol::InitializeParams;
 use crate::protocol::InitializeResponse;
 use crate::protocol::ReadParams;
 use crate::protocol::ReadResponse;
+use crate::protocol::SignalParams;
+use crate::protocol::SignalResponse;
 use crate::protocol::TerminateParams;
 use crate::protocol::TerminateResponse;
 use crate::protocol::WriteParams;
@@ -171,6 +173,14 @@ impl ExecServerHandler {
         session.process().exec_write(params).await
     }
 
+    pub(crate) async fn signal(
+        &self,
+        params: SignalParams,
+    ) -> Result<SignalResponse, JSONRPCErrorError> {
+        let session = self.require_initialized_for("exec")?;
+        session.process().signal(params).await
+    }
+
     pub(crate) async fn terminate(
         &self,
         params: TerminateParams,

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

@@ -5,6 +5,8 @@ use crate::protocol::ExecParams;
 use crate::protocol::ExecResponse;
 use crate::protocol::ReadParams;
 use crate::protocol::ReadResponse;
+use crate::protocol::SignalParams;
+use crate::protocol::SignalResponse;
 use crate::protocol::TerminateParams;
 use crate::protocol::TerminateResponse;
 use crate::protocol::WriteParams;
@@ -49,6 +51,13 @@ impl ProcessHandler {
         self.process.exec_write(params).await
     }
 
+    pub(crate) async fn signal(
+        &self,
+        params: SignalParams,
+    ) -> Result<SignalResponse, JSONRPCErrorError> {
+        self.process.signal_process(params).await
+    }
+
     pub(crate) async fn terminate(
         &self,
         params: TerminateParams,

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

@@ -3,6 +3,7 @@ use std::sync::Arc;
 use crate::protocol::ENVIRONMENT_INFO_METHOD;
 use crate::protocol::EXEC_METHOD;
 use crate::protocol::EXEC_READ_METHOD;
+use crate::protocol::EXEC_SIGNAL_METHOD;
 use crate::protocol::EXEC_TERMINATE_METHOD;
 use crate::protocol::EXEC_WRITE_METHOD;
 use crate::protocol::ExecParams;
@@ -32,6 +33,7 @@ use crate::protocol::INITIALIZE_METHOD;
 use crate::protocol::INITIALIZED_METHOD;
 use crate::protocol::InitializeParams;
 use crate::protocol::ReadParams;
+use crate::protocol::SignalParams;
 use crate::protocol::TerminateParams;
 use crate::protocol::WriteParams;
 use crate::rpc::RpcRouter;
@@ -77,6 +79,12 @@ pub(crate) fn build_router() -> RpcRouter<ExecServerHandler> {
             handler.exec_write(params).await
         },
     );
+    router.request(
+        EXEC_SIGNAL_METHOD,
+        |handler: Arc<ExecServerHandler>, params: SignalParams| async move {
+            handler.signal(params).await
+        },
+    );
     router.request(
         EXEC_TERMINATE_METHOD,
         |handler: Arc<ExecServerHandler>, params: TerminateParams| async move {

codex-rs/exec-server/tests/exec_process.rs

@@ -1,5 +1,3 @@
-#![cfg(unix)]
-
 mod common;
 
 use std::sync::Arc;
@@ -13,6 +11,7 @@ use codex_exec_server::ExecParams;
 use codex_exec_server::ExecProcess;
 use codex_exec_server::ExecProcessEvent;
 use codex_exec_server::ProcessId;
+use codex_exec_server::ProcessSignal;
 use codex_exec_server::ReadResponse;
 use codex_exec_server::StartedExecProcess;
 use codex_exec_server::WriteStatus;
@@ -505,6 +504,98 @@ async fn assert_exec_process_rejects_write_without_pipe_stdin(use_remote: bool)
     Ok(())
 }
 
+async fn assert_exec_process_signal_interrupts_process(use_remote: bool) -> Result<()> {
+    let context = create_process_context(use_remote).await?;
+    let process_id = "proc-signal".to_string();
+    let session = context
+        .backend
+        .start(ExecParams {
+            process_id: process_id.clone().into(),
+            argv: vec![
+                "/bin/sh".to_string(),
+                "-c".to_string(),
+                "trap 'printf \"signal:2\\n\"; exit 7' INT; printf 'ready\\n'; while :; do :; done".to_string(),
+            ],
+            cwd: std::env::current_dir()?,
+            env_policy: /*env_policy*/ None,
+            env: Default::default(),
+            tty: false,
+            pipe_stdin: false,
+            arg0: None,
+        })
+        .await?;
+    assert_eq!(session.process.process_id().as_str(), process_id);
+
+    let StartedExecProcess { process } = session;
+    let mut wake_rx = process.subscribe_wake();
+    let mut ready_output = String::new();
+    let mut after_seq = None;
+    loop {
+        let response =
+            read_process_until_change(Arc::clone(&process), &mut wake_rx, after_seq).await?;
+        for chunk in response.chunks {
+            ready_output.push_str(&String::from_utf8_lossy(&chunk.chunk.into_inner()));
+            after_seq = Some(chunk.seq);
+        }
+        if ready_output.contains("ready\n") {
+            break;
+        }
+        if response.closed {
+            anyhow::bail!("process closed before readiness marker: {ready_output:?}");
+        }
+        after_seq = response.next_seq.checked_sub(1).or(after_seq);
+    }
+
+    process.signal(ProcessSignal::Interrupt).await?;
+    let (output, exit_code, closed) = collect_process_output_from_reads(process, wake_rx).await?;
+
+    assert!(
+        output.contains("signal:2"),
+        "expected signal handler output, got {output:?}"
+    );
+    assert_eq!(exit_code, Some(7));
+    assert!(closed);
+    Ok(())
+}
+
+async fn assert_exec_process_signal_reports_unsupported_on_windows(use_remote: bool) -> Result<()> {
+    let context = create_process_context(use_remote).await?;
+    let session = context
+        .backend
+        .start(ExecParams {
+            process_id: ProcessId::from("proc-windows-signal"),
+            argv: vec![
+                "cmd".to_string(),
+                "/C".to_string(),
+                "echo ready && ping -n 30 127.0.0.1 >NUL".to_string(),
+            ],
+            cwd: std::env::current_dir()?,
+            env_policy: /*env_policy*/ None,
+            env: Default::default(),
+            tty: false,
+            pipe_stdin: false,
+            arg0: None,
+        })
+        .await?;
+
+    let err = match session.process.signal(ProcessSignal::Interrupt).await {
+        Ok(()) => anyhow::bail!("Windows non-TTY signal should report unsupported"),
+        Err(err) => err,
+    };
+    let message = err.to_string();
+    assert!(
+        message.contains("failed to signal process"),
+        "unexpected signal error: {message}"
+    );
+    assert!(
+        message.contains("process interrupt is not supported by this process backend"),
+        "unexpected signal error: {message}"
+    );
+
+    session.process.terminate().await?;
+    Ok(())
+}
+
 async fn assert_exec_process_preserves_queued_events_before_subscribe(
     use_remote: bool,
 ) -> Result<()> {
@@ -539,6 +630,7 @@ async fn assert_exec_process_preserves_queued_events_before_subscribe(
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
 async fn remote_exec_process_reports_transport_disconnect() -> Result<()> {
@@ -630,6 +722,7 @@ async fn remote_exec_process_reports_transport_disconnect() -> Result<()> {
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -639,6 +732,7 @@ async fn exec_process_starts_and_exits(use_remote: bool) -> Result<()> {
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -648,6 +742,7 @@ async fn exec_process_streams_output(use_remote: bool) -> Result<()> {
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -657,6 +752,7 @@ async fn exec_process_pushes_events(use_remote: bool) -> Result<()> {
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -666,6 +762,7 @@ async fn exec_process_replays_events_after_close(use_remote: bool) -> Result<()>
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -677,6 +774,7 @@ async fn exec_process_retains_output_after_exit_until_streams_close(
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -686,6 +784,7 @@ async fn exec_process_write_then_read(use_remote: bool) -> Result<()> {
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -695,6 +794,7 @@ async fn exec_process_write_then_read_without_tty(use_remote: bool) -> Result<()
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]
@@ -704,6 +804,27 @@ async fn exec_process_rejects_write_without_pipe_stdin(use_remote: bool) -> Resu
 
 #[test_case(false ; "local")]
 #[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+// Serialize tests that launch a real exec-server process through the full CLI.
+#[serial_test::serial(remote_exec_server)]
+async fn exec_process_signal_interrupts_process(use_remote: bool) -> Result<()> {
+    assert_exec_process_signal_interrupts_process(use_remote).await
+}
+
+#[test_case(false ; "local")]
+#[test_case(true ; "remote")]
+#[cfg_attr(not(windows), ignore = "Windows-only exec-server process test")]
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+// Serialize tests that launch a real exec-server process through the full CLI.
+#[serial_test::serial(remote_exec_server)]
+async fn exec_process_signal_reports_unsupported_on_windows(use_remote: bool) -> Result<()> {
+    assert_exec_process_signal_reports_unsupported_on_windows(use_remote).await
+}
+
+#[test_case(false ; "local")]
+#[test_case(true ; "remote")]
+#[cfg_attr(not(unix), ignore = "Unix-only exec-server process test")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 // Serialize tests that launch a real exec-server process through the full CLI.
 #[serial_test::serial(remote_exec_server)]