fix heart refill and grant unlimited hearts to active subscribers

next_refill_at was set on UserHearts but never read or recalculated,
so a heart lost to zero never came back. UserHearts.apply_regen() now
catches up missed 24h intervals on read/deduct, and lose_heart() starts
the timer only when it isn't already running.

Any user with an active (non-expired) subscription now skips heart
deduction entirely, regardless of which plan they're on — good enough
for now until per-plan perks are needed.

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

content/tests.py

@@ -1,12 +1,15 @@
+from datetime import timedelta
 from unittest.mock import patch
 
 from django.test import TestCase
+from django.utils import timezone
 from rest_framework.test import APIClient
 from rest_framework.throttling import ScopedRateThrottle
 
 from accounts.authentication import issue_access_token
 from accounts.models import User
 from progress.models import UserHearts, UserStats
+from subscription.models import Plan, Subscription
 
 from .models import Choice, Grade, Lesson, Node, NodeProgress, Question, Unit, UserAnswer, UserLessonCompletion
 
@@ -636,6 +639,63 @@ class GradesListCacheTests(TestCase):
         self.assertEqual(len(r3.data['grades']), 2)
 
 
+class UnlimitedHeartsSubscriptionTests(TestCase):
+    """رگرسیون: هر مشترکِ فعال (فارغ از پلن) نباید با جوابِ غلط هارت از دست بده."""
+
+    def setUp(self):
+        self.client = APIClient()
+        self.user = User.objects.create(device_id='dev-unlimited-hearts', is_guest=True, name='')
+        self.token = issue_access_token(self.user.id)
+
+        grade = Grade.objects.create(title='پایه اول', icon='icon', color='#fff')
+        unit = Unit.objects.create(grade=grade, title='فصل ۱', order=1)
+        node = Node.objects.create(unit=unit, title='گره ۱', order=1)
+        lesson = Lesson.objects.create(node=node, title='درس ۱', intro_text='...')
+        self.question = Question.objects.create(lesson=lesson, type='multiple_choice', prompt='سوال ۱')
+        Choice.objects.create(question=self.question, value='درست', is_correct=True)
+        self.wrong_choice = Choice.objects.create(question=self.question, value='غلط', is_correct=False)
+
+    def _answer_wrong(self):
+        return self.client.post(
+            f'/api/questions/{self.question.id}/answer',
+            {'selectedOptionId': str(self.wrong_choice.id)},
+            format='json',
+            HTTP_AUTHORIZATION=f'Bearer {self.token}',
+        )
+
+    def test_wrong_answer_costs_a_heart_without_subscription(self):
+        UserHearts.objects.create(user_id=self.user.id, current_hearts=5, max_hearts=5)
+
+        response = self._answer_wrong()
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.data['heartsRemaining'], 4)
+
+    def test_wrong_answer_does_not_cost_a_heart_with_active_subscription(self):
+        UserHearts.objects.create(user_id=self.user.id, current_hearts=5, max_hearts=5)
+        plan = Plan.objects.create(title='ماهانه', price=100000)
+        Subscription.objects.create(
+            user_id=self.user.id, plan=plan, status='active',
+            expires_at=timezone.now() + timedelta(days=30),
+        )
+
+        response = self._answer_wrong()
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.data['heartsRemaining'], 5)
+        self.assertEqual(UserHearts.objects.get(user_id=self.user.id).current_hearts, 5)
+
+    def test_expired_subscription_still_costs_a_heart(self):
+        UserHearts.objects.create(user_id=self.user.id, current_hearts=5, max_hearts=5)
+        plan = Plan.objects.create(title='ماهانه', price=100000)
+        Subscription.objects.create(
+            user_id=self.user.id, plan=plan, status='active',
+            expires_at=timezone.now() - timedelta(days=1),
+        )
+
+        response = self._answer_wrong()
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.data['heartsRemaining'], 4)
+
+
 class ReadThrottleTests(TestCase):
     def setUp(self):
         _django_cache.clear()