diff --git a/codex-rs/exec-server/src/connection.rs b/codex-rs/exec-server/src/connection.rs
index 4c1ea63062..9d88a41a0c 100644
--- a/codex-rs/exec-server/src/connection.rs
+++ b/codex-rs/exec-server/src/connection.rs
@@ -722,12 +722,17 @@ mod tests {
     #[tokio::test]
     async fn websocket_connection_keeps_outbound_message_while_send_is_backpressured()
     -> anyhow::Result<()> {
-        let (websocket, control, mut outbound_rx) = ControlledWebSocket::new(false);
-        let mut connection =
-            JsonRpcConnection::from_websocket_stream(websocket, "test".into(), None);
+        let (websocket, control, mut outbound_rx) =
+            ControlledWebSocket::new(/*write_ready*/ false);
+        let mut connection = JsonRpcConnection::from_websocket_stream(
+            websocket,
+            "test".into(),
+            /*ping_interval*/ None,
+        );
         let message = test_jsonrpc_message();
 
         connection.outgoing_tx.send(message.clone()).await?;
+        control.wait_for_blocked_write().await?;
         control.send_inbound(Message::Ping(b"check".to_vec().into()))?;
         assert!(
             timeout(Duration::from_millis(50), connection.incoming_rx.recv())
@@ -777,12 +782,16 @@ mod tests {
         inbound_rx: futures_mpsc::UnboundedReceiver<Result<Message, std::convert::Infallible>>,
         outbound_tx: futures_mpsc::UnboundedSender<Message>,
         write_ready: Arc<AtomicBool>,
+        write_blocked: Arc<AtomicBool>,
+        write_blocked_waker: Arc<AtomicWaker>,
         write_waker: Arc<AtomicWaker>,
     }
 
     struct ControlledWebSocketHandle {
         inbound_tx: futures_mpsc::UnboundedSender<Result<Message, std::convert::Infallible>>,
         write_ready: Arc<AtomicBool>,
+        write_blocked: Arc<AtomicBool>,
+        write_blocked_waker: Arc<AtomicWaker>,
         write_waker: Arc<AtomicWaker>,
     }
 
@@ -797,17 +806,23 @@ mod tests {
             let (inbound_tx, inbound_rx) = futures_mpsc::unbounded();
             let (outbound_tx, outbound_rx) = futures_mpsc::unbounded();
             let write_ready = Arc::new(AtomicBool::new(write_ready));
+            let write_blocked = Arc::new(AtomicBool::new(false));
+            let write_blocked_waker = Arc::new(AtomicWaker::new());
             let write_waker = Arc::new(AtomicWaker::new());
             (
                 Self {
                     inbound_rx,
                     outbound_tx,
                     write_ready: Arc::clone(&write_ready),
+                    write_blocked: Arc::clone(&write_blocked),
+                    write_blocked_waker: Arc::clone(&write_blocked_waker),
                     write_waker: Arc::clone(&write_waker),
                 },
                 ControlledWebSocketHandle {
                     inbound_tx,
                     write_ready,
+                    write_blocked,
+                    write_blocked_waker,
                     write_waker,
                 },
                 outbound_rx,
@@ -826,6 +841,22 @@ mod tests {
             self.write_ready.store(true, Ordering::Release);
             self.write_waker.wake();
         }
+
+        async fn wait_for_blocked_write(&self) -> anyhow::Result<()> {
+            timeout(
+                Duration::from_secs(1),
+                futures::future::poll_fn(|cx| {
+                    if self.write_blocked.load(Ordering::Acquire) {
+                        Poll::Ready(())
+                    } else {
+                        self.write_blocked_waker.register(cx.waker());
+                        Poll::Pending
+                    }
+                }),
+            )
+            .await?;
+            Ok(())
+        }
     }
 
     impl Sink<Message> for ControlledWebSocket {
@@ -835,6 +866,8 @@ mod tests {
             if self.write_ready.load(Ordering::Acquire) {
                 Poll::Ready(Ok(()))
             } else {
+                self.write_blocked.store(true, Ordering::Release);
+                self.write_blocked_waker.wake();
                 self.write_waker.register(cx.waker());
                 Poll::Pending
             }
diff --git a/codex-rs/exec-server/src/relay.rs b/codex-rs/exec-server/src/relay.rs
index 7d3751c67d..4dd607a305 100644
--- a/codex-rs/exec-server/src/relay.rs
+++ b/codex-rs/exec-server/src/relay.rs
@@ -622,7 +622,8 @@ mod tests {
     #[tokio::test]
     async fn harness_connection_keeps_outbound_frame_while_send_is_backpressured()
     -> anyhow::Result<()> {
-        let (websocket, control, mut outbound_rx) = ControlledWebSocket::new(true);
+        let (websocket, control, mut outbound_rx) =
+            ControlledWebSocket::new(/*write_ready*/ true);
         let mut connection = harness_connection_from_websocket(websocket, "test".to_string());
         let Message::Binary(resume_payload) = timeout(Duration::from_secs(1), outbound_rx.next())
             .await?
@@ -635,6 +636,7 @@ mod tests {
 
         control.set_write_blocked();
         connection.outgoing_tx.send(message.clone()).await?;
+        control.wait_for_blocked_write().await?;
         control.send_inbound(Message::Ping(b"check".to_vec().into()))?;
         assert!(
             timeout(Duration::from_millis(50), connection.incoming_rx.recv())
@@ -722,12 +724,16 @@ mod tests {
         inbound_rx: futures_mpsc::UnboundedReceiver<Result<Message, std::convert::Infallible>>,
         outbound_tx: futures_mpsc::UnboundedSender<Message>,
         write_ready: Arc<AtomicBool>,
+        write_blocked: Arc<AtomicBool>,
+        write_blocked_waker: Arc<AtomicWaker>,
         write_waker: Arc<AtomicWaker>,
     }
 
     struct ControlledWebSocketHandle {
         inbound_tx: futures_mpsc::UnboundedSender<Result<Message, std::convert::Infallible>>,
         write_ready: Arc<AtomicBool>,
+        write_blocked: Arc<AtomicBool>,
+        write_blocked_waker: Arc<AtomicWaker>,
         write_waker: Arc<AtomicWaker>,
     }
 
@@ -742,17 +748,23 @@ mod tests {
             let (inbound_tx, inbound_rx) = futures_mpsc::unbounded();
             let (outbound_tx, outbound_rx) = futures_mpsc::unbounded();
             let write_ready = Arc::new(AtomicBool::new(write_ready));
+            let write_blocked = Arc::new(AtomicBool::new(false));
+            let write_blocked_waker = Arc::new(AtomicWaker::new());
             let write_waker = Arc::new(AtomicWaker::new());
             (
                 Self {
                     inbound_rx,
                     outbound_tx,
                     write_ready: Arc::clone(&write_ready),
+                    write_blocked: Arc::clone(&write_blocked),
+                    write_blocked_waker: Arc::clone(&write_blocked_waker),
                     write_waker: Arc::clone(&write_waker),
                 },
                 ControlledWebSocketHandle {
                     inbound_tx,
                     write_ready,
+                    write_blocked,
+                    write_blocked_waker,
                     write_waker,
                 },
                 outbound_rx,
@@ -775,6 +787,22 @@ mod tests {
             self.write_ready.store(true, Ordering::Release);
             self.write_waker.wake();
         }
+
+        async fn wait_for_blocked_write(&self) -> anyhow::Result<()> {
+            timeout(
+                Duration::from_secs(1),
+                futures::future::poll_fn(|cx| {
+                    if self.write_blocked.load(Ordering::Acquire) {
+                        Poll::Ready(())
+                    } else {
+                        self.write_blocked_waker.register(cx.waker());
+                        Poll::Pending
+                    }
+                }),
+            )
+            .await?;
+            Ok(())
+        }
     }
 
     impl Sink<Message> for ControlledWebSocket {
@@ -784,6 +812,8 @@ mod tests {
             if self.write_ready.load(Ordering::Acquire) {
                 Poll::Ready(Ok(()))
             } else {
+                self.write_blocked.store(true, Ordering::Release);
+                self.write_blocked_waker.wake();
                 self.write_waker.register(cx.waker());
                 Poll::Pending
             }