cache the subscription plans list

subscription/views.py
  - PlansListView: served from cache (subscription:plans:v1, 1h TTL);
    plans change ~never and the list is read on every subscription screen.
subscription/receivers.py (new)
  - post_save/post_delete on Plan -> cache.delete(PLANS_CACHE_KEY).
subscription/apps.py
  - SubscriptionConfig.ready() imports receivers.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

subscription/apps.py

@@ -4,3 +4,6 @@ from django.apps import AppConfig
 class SubscriptionConfig(AppConfig):
     default_auto_field = 'django.db.models.BigAutoField'
     name = 'subscription'
+
+    def ready(self):
+        from . import receivers  # noqa: F401  (باطل‌کردنِ کشِ پلن‌ها)

subscription/receivers.py

@@ -0,0 +1,14 @@
+"""باطل‌کردنِ کشِ لیستِ پلن‌ها با هر تغییرِ Plan (از ادمین)."""
+from django.core.cache import cache
+from django.db.models.signals import post_delete, post_save
+from django.dispatch import receiver
+
+from .models import Plan
+
+PLANS_CACHE_KEY = 'subscription:plans:v1'  # هم‌تراز با subscription/views.py
+
+
+@receiver(post_save, sender=Plan, dispatch_uid='subscription_invalidate_plans_cache_on_save')
+@receiver(post_delete, sender=Plan, dispatch_uid='subscription_invalidate_plans_cache_on_delete')
+def _invalidate_plans_cache(sender, **kwargs):
+    cache.delete(PLANS_CACHE_KEY)

subscription/views.py

@@ -1,3 +1,4 @@
+from django.core.cache import cache
 from django.db import transaction
 from django.db.models import F
 from django.shortcuts import get_object_or_404
@@ -38,13 +39,19 @@ class GuestAwarePurchaseThrottle(ScopedRateThrottle):
         return self.cache_format % {'scope': self.scope, 'ident': ident}
 
 
+# پلن‌ها تقریباً هیچ‌وقت عوض نمی‌شوند و روی صفحه‌ی اشتراک هر بار خوانده می‌شوند.
+# با هر save/delete روی Plan کش باطل می‌شود (subscription/receivers.py).
+PLANS_CACHE_KEY = 'subscription:plans:v1'
+PLANS_CACHE_TTL = 3600
+
+
 class PlansListView(APIView):
     """GET /api/subscription/plans — list available plans."""
 
     @extend_schema(responses=PlansListResponseSerializer, tags=['Subscription (subscription)'])
     def get(self, request):
-        plans = Plan.objects.all()
+        def build():
-        data = {
+            return {
                 'plans': [
                     {
                         'id': str(p.id),
@@ -55,9 +62,11 @@ class PlansListView(APIView):
                         'discountPercent': p.discount_percent,
                         'durationDays': p.duration_days,
                     }
-                for p in plans
+                    for p in Plan.objects.all()
                 ]
             }
+
+        data = cache.get_or_set(PLANS_CACHE_KEY, build, PLANS_CACHE_TTL)
         return Response(PlansListResponseSerializer(data).data)