feat(tui): add /app desktop handoff (#25638)

codex-rs/tui/src/chatwidget/slash_dispatch.rs

@@ -202,6 +202,16 @@ impl ChatWidget {
             SlashCommand::Fork => {
                 self.app_event_tx.send(AppEvent::ForkCurrentSession);
             }
+            SlashCommand::App => {
+                let Some(thread_id) = self.thread_id else {
+                    self.add_error_message(
+                        "Session is still starting; try /app again in a moment.".to_string(),
+                    );
+                    return;
+                };
+                self.app_event_tx
+                    .send(AppEvent::OpenDesktopThread { thread_id });
+            }
             SlashCommand::Init => {
                 let init_target = self.config.cwd.join(DEFAULT_AGENTS_MD_FILENAME);
                 if init_target.exists() {
@@ -974,6 +984,7 @@ impl ChatWidget {
             | SlashCommand::Raw
             | SlashCommand::Vim
             | SlashCommand::Diff
+            | SlashCommand::App
             | SlashCommand::Rename
             | SlashCommand::TestApproval => QueueDrain::Continue,
             SlashCommand::Feedback

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__slash_app_without_thread_id_shows_starting_error.snap

@@ -0,0 +1,5 @@
+---
+source: tui/src/chatwidget/tests/slash_commands.rs
+expression: "lines_to_single_string(&cells[0])"
+---
+■ Session is still starting; try /app again in a moment.

codex-rs/tui/src/chatwidget/tests/slash_commands.rs

@@ -2052,6 +2052,36 @@ async fn slash_fork_requests_current_fork() {
     assert_matches!(rx.try_recv(), Ok(AppEvent::ForkCurrentSession));
 }
 
+#[tokio::test]
+async fn slash_app_requests_desktop_handoff() {
+    let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    let thread_id = ThreadId::new();
+    chat.thread_id = Some(thread_id);
+
+    chat.dispatch_command(SlashCommand::App);
+
+    assert_matches!(
+        rx.try_recv(),
+        Ok(AppEvent::OpenDesktopThread {
+            thread_id: actual_thread_id,
+        }) if actual_thread_id == thread_id
+    );
+}
+
+#[tokio::test]
+async fn slash_app_without_thread_id_shows_starting_error() {
+    let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+
+    chat.dispatch_command(SlashCommand::App);
+
+    let cells = drain_insert_history(&mut rx);
+    assert_eq!(cells.len(), 1, "expected app startup error");
+    assert_chatwidget_snapshot!(
+        "slash_app_without_thread_id_shows_starting_error",
+        lines_to_single_string(&cells[0])
+    );
+}
+
 #[tokio::test]
 async fn slash_rollout_displays_current_path() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;