test: cross-file stub-scoping repairs — hub ConfigFlow base carries the full plumbing, standalone rebuilds when its holder is gone, test_init scoped hygiene mirrors scoped_stubs (completes t30 G6)

tests/test_standalone_setup.py

@@ -37,8 +37,15 @@ _STUB_NAMES = (
 
 
 def _install_stubs() -> None:
-    """Import-time stand-ins (idempotent; same shape as the pairing tests)."""
-    if sys.modules.get("voluptuous") is not None:
+    """Import-time stand-ins (idempotent; same shape as the pairing tests).
+
+    t30: the guard rebuilds whenever the module-level holder is missing —
+    a later file's scoped teardown may pop the shared stubs this file's
+    tests rely on (the flow-class surfaces live on the local base which we
+    MUST rebind against)."""
+    if sys.modules.get("voluptuous") is not None and hasattr(
+        sys.modules.get(__name__), "_zc_holder"
+    ):
         return
 
     vol = types.ModuleType("voluptuous")