fix: preserve points balance across account re-registration

Persist a per-email balance snapshot before account deletion and restore it on same-email re-registration, preventing both unintended balance reset and repeated signup bonus grants.

backend/tests/unit/test_points_service_audit.py

@@ -7,6 +7,7 @@ from uuid import UUID, uuid4
 import pytest
 
 from core.config.settings import config
+from models.register_bonus_claims import RegisterBonusClaims
 from schemas.domain.points import AppendAuditLedgerCommand, ApplyPointsChangeCommand
 from schemas.domain.points import PointsChargeSnapshot
 from v1.points.service import PointsService
@@ -28,6 +29,7 @@ class _FakePointsRepository:
         self.appended_ledger: list[ApplyPointsChangeCommand] = []
         self.appended_audit: list[AppendAuditLedgerCommand] = []
         self.claimed: bool = False
+        self.claim: RegisterBonusClaims | None = None
 
     async def get_or_create_user_points_for_update(
         self, *, user_id: UUID
@@ -69,15 +71,23 @@ class _FakePointsRepository:
         *,
         email_hash: str,
         user_email_snapshot: str,
-        first_user_id: UUID,
+        first_user_id_snapshot: UUID,
         grant_event_id: str,
     ) -> bool:
-        del email_hash, user_email_snapshot, first_user_id, grant_event_id
+        del email_hash, user_email_snapshot, first_user_id_snapshot, grant_event_id
         if self.claimed:
             return False
         self.claimed = True
         return True
 
+    async def get_register_bonus_claim(
+        self,
+        *,
+        email_hash: str,
+    ) -> RegisterBonusClaims | None:
+        del email_hash
+        return self.claim
+
 
 @pytest.mark.asyncio
 async def test_consume_successful_run_points_writes_real_usage_to_audit() -> None:
@@ -188,3 +198,30 @@ async def test_grant_register_bonus_if_eligible_second_time_skips() -> None:
     assert result.amount == 0
     assert len(repository.appended_ledger) == 0
     assert len(repository.appended_audit) == 0
+
+
+@pytest.mark.asyncio
+async def test_grant_register_bonus_if_eligible_restores_balance_snapshot() -> None:
+    repository = _FakePointsRepository(usage_snapshot=None)
+    repository.account.balance = 0
+    repository.claim = RegisterBonusClaims(
+        email_hash="abc",
+        user_email_snapshot="restore@example.com",
+        first_user_id_snapshot=uuid4(),
+        balance_snapshot=35,
+        grant_event_id="event",
+    )
+    service = PointsService(repository=repository)  # type: ignore[arg-type]
+
+    result = await service.grant_register_bonus_if_eligible(
+        user_id=uuid4(),
+        user_email="restore@example.com",
+    )
+
+    assert result.granted is False
+    assert result.amount == 0
+    assert result.balance_after == 35
+    assert repository.account.balance == 35
+    assert repository.claimed is False
+    assert len(repository.appended_ledger) == 0
+    assert len(repository.appended_audit) == 0