feat: add plugin runtime and cross-device task orchestration

tests/conftest.py

@@ -46,6 +46,17 @@ def mock_driver():
     return MockDeviceDriver(device_id="fixture-mock-device", width=1080, height=2400)
 
 
+@pytest.fixture(autouse=True)
+def isolated_plugin_registry(monkeypatch, tmp_path, request):
+    """Unit tests never load or mutate the user's installed plugins and credentials."""
+    if any(
+        request.node.get_closest_marker(name)
+        for name in ("android", "integration", "e2e", "manual")
+    ):
+        return
+    monkeypatch.setattr("artemis.plugins.store.get_app_dir", lambda: tmp_path / "app")
+
+
 def pytest_collection_modifyitems(items: list[pytest.Item]) -> None:
     """Attach test-layer markers according to the owning test directory."""
     for item in items: