List body names to confirm, expect "tray" and "puck".

tray_sim.py

@@ -144,4 +144,9 @@ def run_tray_simulation(
 
     print(f"Bodies: {model.nbody}, qpos size: {model.nq}, qvel size: {model.nv}")
 
+    for i in range(model.nbody):
+        name = mujoco.mj_id2name(model, mujoco.mjtObj.mjOBJ_BODY, i)
+        if name:
+            print(f"Body {i}: {name}")
+
     return gif_path, physics_state, json_path