fix: tighten check-in token handling

backend/checkins/test_services.py

@@ -74,6 +74,17 @@ class CheckInServiceTests(TestCase):
         with self.assertRaises(InvalidToken):
             preview_check_in_token(raw_token, staff_user=self.staff_user)
 
+    def test_preview_rejects_expired_check_in_token(self):
+        reservation = self.create_reservation()
+        _, raw_token = ReservationToken.create_token(
+            reservation=reservation,
+            purpose=ReservationToken.Purpose.CHECK_IN,
+            expires_at=timezone.now() - timedelta(minutes=1),
+        )
+
+        with self.assertRaises(InvalidToken):
+            preview_check_in_token(raw_token, staff_user=self.staff_user)
+
     def test_check_in_succeeds_for_confirmed_reservation(self):
         reservation = self.create_reservation()
         _, raw_token = self.create_check_in_token(reservation)
@@ -158,6 +169,14 @@ class CheckInServiceTests(TestCase):
         with self.assertRaises(InvalidToken):
             confirm_check_in_from_token(raw_token, staff_user=self.staff_user)
 
+    def test_check_in_rejects_used_check_in_token(self):
+        reservation = self.create_reservation()
+        token, raw_token = self.create_check_in_token(reservation)
+        token.mark_used()
+
+        with self.assertRaises(InvalidToken):
+            confirm_check_in_from_token(raw_token, staff_user=self.staff_user)
+
     def create_reservation(self, **overrides):
         data = {
             "performance": self.performance,