Cache keyboard enhancement detection before event streams (#3950)

Hopefully fixes incorrectly showing ^J instead of Shift+Enter in the key
hints occasionally.

codex-rs/tui/src/app.rs

@@ -22,7 +22,6 @@ use color_eyre::eyre::WrapErr;
 use crossterm::event::KeyCode;
 use crossterm::event::KeyEvent;
 use crossterm::event::KeyEventKind;
-use crossterm::terminal::supports_keyboard_enhancement;
 use ratatui::style::Stylize;
 use ratatui::text::Line;
 use std::path::PathBuf;
@@ -85,7 +84,7 @@ impl App {
 
         let conversation_manager = Arc::new(ConversationManager::new(auth_manager.clone()));
 
-        let enhanced_keys_supported = supports_keyboard_enhancement().unwrap_or(false);
+        let enhanced_keys_supported = tui.enhanced_keys_supported();
 
         let chat_widget = match resume_selection {
             ResumeSelection::StartFresh | ResumeSelection::Exit => {

codex-rs/tui/src/tui.rs

@@ -27,6 +27,7 @@ use crossterm::event::PopKeyboardEnhancementFlags;
 use crossterm::event::PushKeyboardEnhancementFlags;
 use crossterm::terminal::EnterAlternateScreen;
 use crossterm::terminal::LeaveAlternateScreen;
+use crossterm::terminal::supports_keyboard_enhancement;
 use ratatui::backend::Backend;
 use ratatui::backend::CrosstermBackend;
 use ratatui::crossterm::execute;
@@ -160,6 +161,7 @@ pub struct Tui {
     alt_screen_active: Arc<AtomicBool>,
     // True when terminal/tab is focused; updated internally from crossterm events
     terminal_focused: Arc<AtomicBool>,
+    enhanced_keys_supported: bool,
 }
 
 #[cfg(unix)]
@@ -266,6 +268,10 @@ impl Tui {
             }
         });
 
+        // Detect keyboard enhancement support before any EventStream is created so the
+        // crossterm poller can acquire its lock without contention.
+        let enhanced_keys_supported = supports_keyboard_enhancement().unwrap_or(false);
+
         Self {
             frame_schedule_tx,
             draw_tx,
@@ -278,6 +284,7 @@ impl Tui {
             suspend_cursor_y: Arc::new(AtomicU16::new(0)),
             alt_screen_active: Arc::new(AtomicBool::new(false)),
             terminal_focused: Arc::new(AtomicBool::new(true)),
+            enhanced_keys_supported,
         }
     }
 
@@ -287,6 +294,10 @@ impl Tui {
         }
     }
 
+    pub fn enhanced_keys_supported(&self) -> bool {
+        self.enhanced_keys_supported
+    }
+
     pub fn event_stream(&self) -> Pin<Box<dyn Stream<Item = TuiEvent> + Send + 'static>> {
         use tokio_stream::StreamExt;
         let mut crossterm_events = crossterm::event::EventStream::new();