diff --git a/tests/cron/conftest.py b/tests/cron/conftest.py
index 256fff1403..b73ec99e93 100644
--- a/tests/cron/conftest.py
+++ b/tests/cron/conftest.py
@@ -45,6 +45,13 @@ def make_cron_provider():
     return _make
 
 
+@pytest.fixture(autouse=True)
+def _no_managed_store(tmp_path, monkeypatch):
+    """Point PM's store at an empty dir: script runs must not select the host install's
+    dependency venv (POSIX cron scripts run on it when a store is committed)."""
+    monkeypatch.setenv("HERMES_RUNTIME_DIR", str(tmp_path / "no-pm-store"))
+
+
 @pytest.fixture(autouse=True)
 def _default_cron_test_model(monkeypatch):
     """Pin a default HERMES_MODEL so cron run_job tests have a resolvable model."""