diff --git a/codex-rs/tui/src/app/session_lifecycle.rs b/codex-rs/tui/src/app/session_lifecycle.rs
index d1a8679f45..fcb21c3ed8 100644
--- a/codex-rs/tui/src/app/session_lifecycle.rs
+++ b/codex-rs/tui/src/app/session_lifecycle.rs
@@ -430,15 +430,15 @@ impl App {
         result: Result<AppServerStartedThread, String>,
     ) -> Result<()> {
         if self.pending_startup_thread_start_request_id.as_deref() != Some(request_id.as_str()) {
-            if let Ok(started) = result
-                && let Err(err) = app_server
-                    .thread_unsubscribe(started.session.thread_id)
-                    .await
-            {
-                tracing::warn!(
-                    thread_id = %started.session.thread_id,
-                    "failed to unsubscribe stale startup thread: {err}"
-                );
+            if let Ok(started) = result {
+                let thread_id = started.session.thread_id;
+                if let Err(err) = app_server.thread_unsubscribe(thread_id).await {
+                    tracing::warn!(
+                        thread_id = %thread_id,
+                        "failed to unsubscribe stale startup thread: {err}"
+                    );
+                }
+                self.discard_thread_local_state(thread_id).await;
             }
             return Ok(());
         }
@@ -453,9 +453,14 @@ impl App {
                 self.chat_widget.maybe_send_next_queued_input();
             }
             Err(err) => {
-                self.chat_widget.add_error_message(format!(
-                    "Failed to start a fresh session through the app server: {err}"
-                ));
+                let message =
+                    format!("Failed to start a fresh session through the app server: {err}");
+                tracing::warn!(
+                    error = %err,
+                    "startup thread/start failed"
+                );
+                self.chat_widget.add_error_message(message.clone());
+                return Err(color_eyre::eyre::eyre!(message));
             }
         }
         Ok(())
diff --git a/codex-rs/tui/src/app/side.rs b/codex-rs/tui/src/app/side.rs
index 044cb9b391..492639f139 100644
--- a/codex-rs/tui/src/app/side.rs
+++ b/codex-rs/tui/src/app/side.rs
@@ -369,15 +369,15 @@ impl App {
             self.chat_widget.add_error_message(message);
             return false;
         }
-        self.discard_side_thread_local(thread_id).await;
+        self.discard_thread_local_state(thread_id).await;
         true
     }
 
     pub(super) async fn discard_closed_side_thread(&mut self, thread_id: ThreadId) {
-        self.discard_side_thread_local(thread_id).await;
+        self.discard_thread_local_state(thread_id).await;
     }
 
-    async fn discard_side_thread_local(&mut self, thread_id: ThreadId) {
+    pub(super) async fn discard_thread_local_state(&mut self, thread_id: ThreadId) {
         self.abort_thread_event_listener(thread_id);
         self.thread_event_channels.remove(&thread_id);
         self.side_threads.remove(&thread_id);
diff --git a/codex-rs/tui/src/app/tests/startup.rs b/codex-rs/tui/src/app/tests/startup.rs
index 6760594e63..305bb8caa4 100644
--- a/codex-rs/tui/src/app/tests/startup.rs
+++ b/codex-rs/tui/src/app/tests/startup.rs
@@ -181,6 +181,86 @@ async fn startup_thread_started_submits_queued_startup_input() {
     }
 }
 
+#[tokio::test]
+async fn startup_thread_start_failure_returns_error() {
+    let (mut app, _app_event_rx, _op_rx) = make_test_app_with_channels().await;
+    let request_id = "startup-thread-start-failed".to_string();
+    app.pending_startup_thread_start_request_id = Some(request_id.clone());
+    app.chat_widget
+        .set_queue_submissions_until_session_configured(/*queue*/ true);
+
+    let mut app_server = Box::pin(crate::start_embedded_app_server_for_picker(
+        app.chat_widget.config_ref(),
+    ))
+    .await
+    .expect("embedded app server");
+    let err = app
+        .handle_startup_thread_started(&mut app_server, request_id, Err("boom".to_string()))
+        .await
+        .expect_err("startup thread failure should exit instead of leaving chat unconfigured");
+
+    assert!(
+        err.to_string()
+            .contains("Failed to start a fresh session through the app server: boom")
+    );
+    assert_eq!(app.pending_startup_thread_start_request_id, None);
+    assert_eq!(app.primary_thread_id, None);
+}
+
+#[test]
+fn stale_startup_thread_started_removes_local_routing_state() -> Result<()> {
+    const WORKER_THREADS: usize = 1;
+    const TEST_STACK_SIZE_BYTES: usize = 8 * 1024 * 1024;
+
+    let runtime = tokio::runtime::Builder::new_multi_thread()
+        .worker_threads(WORKER_THREADS)
+        .thread_stack_size(TEST_STACK_SIZE_BYTES)
+        .enable_all()
+        .build()?;
+
+    runtime.block_on(async {
+        let mut app = make_test_app().await;
+        let mut app_server =
+            crate::start_embedded_app_server_for_picker(app.chat_widget.config_ref()).await?;
+        let stale_started = app_server
+            .start_thread(app.chat_widget.config_ref())
+            .await?;
+        let primary_thread_id = ThreadId::new();
+        let stale_thread_id = stale_started.session.thread_id;
+        app.primary_thread_id = Some(primary_thread_id);
+        app.thread_event_channels.insert(
+            primary_thread_id,
+            ThreadEventChannel::new(THREAD_EVENT_CHANNEL_CAPACITY),
+        );
+        app.activate_thread_channel(primary_thread_id).await;
+        app.thread_event_channels.insert(
+            stale_thread_id,
+            ThreadEventChannel::new(THREAD_EVENT_CHANNEL_CAPACITY),
+        );
+        app.agent_navigation.upsert(
+            stale_thread_id,
+            Some("Stale".to_string()),
+            /*agent_role*/ None,
+            /*is_closed*/ false,
+        );
+        app.pending_startup_thread_start_request_id = Some("newer-startup-request".to_string());
+        assert!(app.thread_event_channels.contains_key(&stale_thread_id));
+        assert!(app.agent_navigation.get(&stale_thread_id).is_some());
+
+        app.handle_startup_thread_started(
+            &mut app_server,
+            "old-startup-request".to_string(),
+            Ok(stale_started),
+        )
+        .await?;
+
+        assert!(!app.thread_event_channels.contains_key(&stale_thread_id));
+        assert_eq!(app.agent_navigation.get(&stale_thread_id), None);
+        assert_eq!(app.active_thread_id, Some(primary_thread_id));
+        Ok(())
+    })
+}
+
 #[tokio::test]
 async fn ignore_same_thread_resume_reports_noop_for_current_thread() {
     let (mut app, mut app_event_rx, _op_rx) = make_test_app_with_channels().await;