diff --git a/tests/conftest.py b/tests/conftest.py
index 2573a3f..79d3dd0 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -53,6 +53,17 @@ def isolated_drive_usage_cache(tmp_path, monkeypatch):
     monkeypatch.setattr('core.drive_usage.cache_path', lambda: tmp_path / 'drive_usage_cache.json')
 
 
+@pytest.fixture(autouse=True)
+def isolated_capacity_workers(monkeypatch, collect_gui_cycles):
+    """No queued capacity read or helper survives into the next test.
+
+    Keep each test's mocks installed while draining its workers; the GUI
+    collector must also remain active until those workers have finished.
+    """
+    yield
+    shutdown_capacity_executor()
+
+
 @pytest.fixture(autouse=True)
 def synchronous_navigation(monkeypatch):
     """Legacy tests expect navigate_to() to take effect at once; tests/test_drive_switch.py covers the async path."""