Fix: Clear ContentType/guardian caches at import and test cases (#12758)

src/documents/tests/conftest.py

@@ -8,6 +8,8 @@ from typing import TYPE_CHECKING
 import filelock
 import pytest
 from django.contrib.auth import get_user_model
+from django.contrib.contenttypes.models import ContentType
+from guardian.shortcuts import clear_ct_cache
 from pytest_django.fixtures import SettingsWrapper
 from rest_framework.test import APIClient
 
@@ -158,6 +160,19 @@ def user_client(rest_api_client: APIClient, regular_user: UserModelT) -> APIClie
     return rest_api_client
 
 
+@pytest.fixture(autouse=True)
+def _clear_content_type_caches() -> None:
+    """Clear Django's ContentType cache and guardian's lru_cache before each test.
+
+    Tests that delete and reinsert ContentType/Permission rows (e.g. the
+    importer) corrupt both caches. Without this fixture a subsequent test on
+    the same xdist worker sees stale ContentType objects and guardian raises
+    MixedContentTypeError.
+    """
+    ContentType.objects.clear_cache()
+    clear_ct_cache()
+
+
 @pytest.fixture(scope="session", autouse=True)
 def faker_session_locale():
     """Set Faker locale for reproducibility."""