refactor(tests): add import-state isolation helper

Test-only refactor continuing #2523. Adds a shared import-state isolation helper with focused coverage and migrates two pilot tests that manually preserved sys.modules and parent package attributes.

tests/test_webhook_ssrf_resilience.py

@@ -2,59 +2,20 @@ import sys
 import json
 from datetime import datetime
 
-# conftest.py stubs src.database with a fake module; webhook_manager imports
-# from it, so drop the stub here to load the real module under test. We RESTORE
-# both the sys.modules entry AND the parent `src` package attribute afterwards,
-# so the real src.database never leaks into sibling test modules (e.g.
-# llm_core.list_model_ids resolves `from src.database import ...` against
-# sys.modules at call time, and `import src.database as X` resolves through the
-# parent attribute). This mirrors the routes.session_routes isolation fix.
-_ABSENT = object()
+import pytest
 
+from tests.helpers.import_state import clear_module, preserve_import_state
 
-def _save_module_and_parent_attr(dotted_name):
-    """Capture a module's sys.modules entry *and* its parent-package attribute.
-
-    Returns a (module, attr) pair to hand back to
-    _restore_module_and_parent_attr. Either may be _ABSENT when not present.
-    """
-    saved_module = sys.modules.get(dotted_name, _ABSENT)
-    pkg_name, _, attr = dotted_name.rpartition(".")
-    pkg = sys.modules.get(pkg_name)
-    saved_attr = getattr(pkg, attr, _ABSENT) if pkg is not None else _ABSENT
-    return saved_module, saved_attr
-
-
-def _restore_module_and_parent_attr(dotted_name, saved_module, saved_attr):
-    """Restore (or remove) both the sys.modules entry and the parent attribute.
-
-    Passing _ABSENT for both clears the cache, which is how we drop the stub
-    before the real import below.
-    """
-    if saved_module is _ABSENT:
-        sys.modules.pop(dotted_name, None)
-    else:
-        sys.modules[dotted_name] = saved_module
-    pkg_name, _, attr = dotted_name.rpartition(".")
-    pkg = sys.modules.get(pkg_name)
-    if pkg is None:
-        return
-    if saved_attr is _ABSENT:
-        if hasattr(pkg, attr):
-            delattr(pkg, attr)
-    else:
-        setattr(pkg, attr, saved_attr)
-
-
-# Capture the stub state, then clear both bindings so webhook_manager's import
-# below produces/binds the real src.database with no stale stub behind it.
-_src_database_saved = _save_module_and_parent_attr("src.database")
-_restore_module_and_parent_attr("src.database", _ABSENT, _ABSENT)
-_core_database = sys.modules.get("core.database")
-_core_database_all = getattr(_core_database, "__all__", None) if _core_database is not None else None
-if (
-    _core_database is not None
-    and (
+# conftest.py stubs src.database; drop the stub so webhook_manager imports the
+# real module. preserve_import_state restores both sys.modules and the parent
+# src.database attribute after the block, preventing stub leakage into siblings.
+with preserve_import_state("src.database"):
+    clear_module("src.database")
+    _core_database = sys.modules.get("core.database")
+    _core_database_all = (
+        getattr(_core_database, "__all__", None) if _core_database is not None else None
+    )
+    if _core_database is not None and (
         not getattr(_core_database, "__file__", None)
         or (
             _core_database_all is not None
@@ -63,17 +24,9 @@ if (
                 or not all(isinstance(name, str) for name in _core_database_all)
             )
         )
-    )
-):
-    del sys.modules["core.database"]
-
-import pytest
-from src.webhook_manager import validate_webhook_url
-
-# webhook_manager is now bound to the real src.database, so restore both the
-# sys.modules entry and the parent `src.database` attribute to their original
-# stub state to avoid polluting sibling test modules.
-_restore_module_and_parent_attr("src.database", *_src_database_saved)
+    ):
+        del sys.modules["core.database"]
+    from src.webhook_manager import validate_webhook_url
 
 
 def test_webhook_url_ssrf_mitigation():