fix: stabilize headless rollout and summarize phase1 grid

tests/test_eval_vla_headless_import.py

@@ -0,0 +1,26 @@
+import json
+import os
+import subprocess
+import sys
+
+
+def test_eval_vla_import_does_not_import_mujoco_early_when_headless_backend_not_set():
+    env = os.environ.copy()
+    env.pop('MUJOCO_GL', None)
+    proc = subprocess.run(
+        [
+            sys.executable,
+            '-c',
+            (
+                'import json, sys; '
+                'from roboimi.demos.vla_scripts import eval_vla; '
+                'print(json.dumps({"mujoco_in_sys_modules": "mujoco" in sys.modules}))'
+            ),
+        ],
+        capture_output=True,
+        text=True,
+        env=env,
+        check=True,
+    )
+    payload = json.loads(proc.stdout.strip())
+    assert payload['mujoco_in_sys_modules'] is False