Streaming markdown (#1920)

We wait until we have an entire newline, then format it with markdown and stream in to the UI. This reduces time to first token but is the right thing to do with our current rendering model IMO. Also lets us add word wrapping!

codex-rs/tui/src/app.rs

@@ -64,6 +64,9 @@ pub(crate) struct App<'a> {
     pending_history_lines: Vec<Line<'static>>,
 
     enhanced_keys_supported: bool,
+
+    /// Controls the animation thread that sends CommitTick events.
+    commit_anim_running: Arc<AtomicBool>,
 }
 
 /// Aggregate parameters needed to create a `ChatWidget`, as creation may be
@@ -173,6 +176,7 @@ impl App<'_> {
             file_search,
             pending_redraw,
             enhanced_keys_supported,
+            commit_anim_running: Arc::new(AtomicBool::new(false)),
         }
     }
 
@@ -189,7 +193,7 @@ impl App<'_> {
         // redraw is already pending so we can return early.
         if self
             .pending_redraw
-            .compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst)
+            .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
             .is_err()
         {
             return;
@@ -200,7 +204,7 @@ impl App<'_> {
         thread::spawn(move || {
             thread::sleep(REDRAW_DEBOUNCE);
             tx.send(AppEvent::Redraw);
-            pending_redraw.store(false, Ordering::SeqCst);
+            pending_redraw.store(false, Ordering::Release);
         });
     }
 
@@ -221,6 +225,30 @@ impl App<'_> {
                 AppEvent::Redraw => {
                     std::io::stdout().sync_update(|_| self.draw_next_frame(terminal))??;
                 }
+                AppEvent::StartCommitAnimation => {
+                    if self
+                        .commit_anim_running
+                        .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
+                        .is_ok()
+                    {
+                        let tx = self.app_event_tx.clone();
+                        let running = self.commit_anim_running.clone();
+                        thread::spawn(move || {
+                            while running.load(Ordering::Relaxed) {
+                                thread::sleep(Duration::from_millis(50));
+                                tx.send(AppEvent::CommitTick);
+                            }
+                        });
+                    }
+                }
+                AppEvent::StopCommitAnimation => {
+                    self.commit_anim_running.store(false, Ordering::Release);
+                }
+                AppEvent::CommitTick => {
+                    if let AppState::Chat { widget } = &mut self.app_state {
+                        widget.on_commit_tick();
+                    }
+                }
                 AppEvent::KeyEvent(key_event) => {
                     match key_event {
                         KeyEvent {