fix(flags): added cache invalidation

src/backend/apps/flags/tests/test_flags.py

@@ -1,6 +1,7 @@
 from django.core.exceptions import ValidationError
 from django.test import TestCase
 
+from apps.decision.services import decide_for_flag
 from apps.flags.models import (
     FeatureFlagType,
     validate_value_for_type,
@@ -159,6 +160,20 @@ class FeatureFlagServiceTest(TestCase):
         with self.assertRaises(ValidationError):
             feature_flag_update_default(flag=flag, default_value="bad")
 
+    def test_update_default_invalidates_decide_flag_cache(self) -> None:
+        flag = feature_flag_create(
+            key="svc_upd_cache",
+            name="Update Cache",
+            value_type=FeatureFlagType.STRING,
+            default_value="old",
+        )
+        first = decide_for_flag(flag.key, "svc_subj_1", {})
+        self.assertEqual(first["value"], "old")
+        feature_flag_update_default(flag=flag, default_value="new")
+        second = decide_for_flag(flag.key, "svc_subj_2", {})
+        self.assertEqual(second["reason"], "no_active_experiment")
+        self.assertEqual(second["value"], "new")
+
 
 class FeatureFlagSelectorTest(TestCase):
     def test_list_all(self) -> None: