fix: add ledger refund uniqueness guard

apps/billing/migrations/0003_pointsledger_unique_ledger_change_type_per_call.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.2.15 on 2026-07-02 08:37
+
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('billing', '0002_exchangerate_pricingrule'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.AddConstraint(
+            model_name='pointsledger',
+            constraint=models.UniqueConstraint(fields=('ref_call', 'change_type'), name='unique_ledger_change_type_per_call'),
+        ),
+    ]

apps/billing/models.py

@@ -192,6 +192,10 @@ class PointsLedger(models.Model):
                 condition=~Q(points_delta=0),
                 name="points_ledger_points_delta_non_zero",
             ),
+            models.UniqueConstraint(
+                fields=("ref_call", "change_type"),
+                name="unique_ledger_change_type_per_call",
+            ),
         ]
         indexes = [
             models.Index(fields=("user", "created_at")),

apps/billing/tests.py

@@ -143,6 +143,41 @@ class BillingCoreModelTests(TestCase):
                     balance_after=-1,
                 )
 
+    def test_points_ledger_allows_consume_and_refund_but_rejects_duplicate_refund(self):
+        call = CallRecord.objects.create(
+            user=self.user,
+            operation_type=CallRecord.OperationType.TITLE,
+            alias="title-standard",
+            model_used="gpt-5.5",
+            points_cost=2,
+            status=CallRecord.Status.FAILED,
+        )
+
+        PointsLedger.objects.create(
+            user=self.user,
+            change_type=PointsLedger.ChangeType.CONSUME,
+            points_delta=-2,
+            balance_after=98,
+            ref_call=call,
+        )
+        PointsLedger.objects.create(
+            user=self.user,
+            change_type=PointsLedger.ChangeType.REFUND,
+            points_delta=2,
+            balance_after=100,
+            ref_call=call,
+        )
+
+        with self.assertRaises(IntegrityError):
+            with transaction.atomic():
+                PointsLedger.objects.create(
+                    user=self.user,
+                    change_type=PointsLedger.ChangeType.REFUND,
+                    points_delta=2,
+                    balance_after=102,
+                    ref_call=call,
+                )
+
     def test_billing_models_are_registered_in_admin(self):
         self.assertIn(UserWallet, admin.site._registry)
         self.assertIn(ApiKey, admin.site._registry)