TUI support for buffer experience (#29919)

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

@@ -27,6 +27,7 @@ impl ChatWidget {
         }
         self.refresh_plan_mode_nudge();
         self.turn_lifecycle.reset_thread();
+        self.clear_safety_buffering();
         self.thread_name = session.thread_name.clone();
         self.current_goal_status_indicator = None;
         self.current_goal_status = None;