Enhance overlay camera state management in mujoco_server.py

- Added logic to store a reference to the old renderer before updating the overlay camera state, preventing race conditions.
- Updated the state management to ensure the old renderer is closed only after the new state is set, mitigating use-after-free issues.
- Implemented error handling when closing the old renderer to improve robustness.

mujoco_server.py

@@ -2022,15 +2022,24 @@ def add_camera():
     _store_dynamic_camera_config(robot_type, scene_name, config)
 
     state_payload = _build_overlay_camera_state(config, create_renderer=False)
+
+    # Store reference to old renderer to close after state update (prevents race condition)
+    old_renderer = None
     with overlay_camera_lock:
         if config["name"] in overlay_camera_states:
             old_renderer = overlay_camera_states[config["name"]].get("renderer")
-            if old_renderer:
-                old_renderer.close()
+        # Update state first before closing old renderer to prevent use-after-free
         overlay_camera_states[config["name"]] = state_payload
     with overlay_frame_lock:
         overlay_frames[config["name"]] = None
 
+    # Close old renderer after state is updated (prevents simulation loop from accessing freed renderer)
+    if old_renderer:
+        try:
+            old_renderer.close()
+        except Exception:
+            pass
+
     broadcast_camera_event(
         "added",
         camera_payload,