fix(flags): added cache invalidation

src/backend/apps/flags/services.py

@@ -1,8 +1,13 @@
+from django.core.cache import cache
 from django.core.exceptions import ValidationError
 
 from apps.flags.models import FeatureFlag, FeatureFlagType
 
 
+def _flag_cache_key(flag_key: str) -> str:
+    return f"flag:{flag_key}"
+
+
 def feature_flag_create(
     *,
     key: str,
@@ -28,6 +33,7 @@ def feature_flag_create(
         default_value=default_value,
     )
     flag.save()
+    cache.delete(_flag_cache_key(flag.key))
     return flag
 
 
@@ -38,4 +44,5 @@ def feature_flag_update_default(
 ) -> FeatureFlag:
     flag.default_value = default_value
     flag.save(update_fields=["default_value", "updated_at"])
+    cache.delete(_flag_cache_key(flag.key))
     return flag

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: