Avoid redundant TUI redraws while streaming (#34049)

## What changed

- Redraw assistant and plan stream tails only when a completed line changes the visible tail.
- Cache the first reasoning header and update the status indicator only when its visible state changes, while restoring the cached header if the indicator is recreated.
- Keep regular commit ticks able to clear stale stream tails.

## Testing

- Add coverage for unchanged partial deltas, changed newline-delimited tails, reasoning-header redraws, recreated status indicators, stale plan tails, and history-line draw scheduling.

GitOrigin-RevId: 9016175f97ef2db2edc2fd5ba13a4d731dc2d98c

codex-rs/tui/src/tui.rs

@@ -105,6 +105,7 @@ mod tests {
     use codex_config::types::NotificationCondition;
     use ratatui::layout::Position;
     use ratatui::layout::Rect;
+    use ratatui::text::Line;
 
     #[test]
     fn unfocused_notification_condition_is_suppressed_when_focused() {
@@ -170,6 +171,20 @@ mod tests {
             "expected stale cells inside the new viewport to be cleared, rows: {rows:?}"
         );
     }
+
+    #[tokio::test(flavor = "current_thread", start_paused = true)]
+    async fn inserting_history_lines_schedules_a_draw() {
+        let mut tui = crate::tui::test_support::make_test_tui().expect("test tui");
+        let mut draw_rx = tui.draw_tx.subscribe();
+
+        tui.insert_history_lines(vec![Line::from("committed stream line")]);
+        tokio::time::advance(std::time::Duration::from_millis(20)).await;
+
+        assert!(matches!(
+            tokio::time::timeout(std::time::Duration::from_millis(50), draw_rx.recv()).await,
+            Ok(Ok(()))
+        ));
+    }
 }
 
 pub fn set_modes() -> Result<()> {