第 4 阶段：订单、交接与账务--ok

backend/internal/modules/order/service.go

@@ -10,6 +10,8 @@ var (
 	ErrOrderCannotCancel     = errors.New("order cannot cancel")
 	ErrOrderCannotHandoff    = errors.New("order cannot handoff")
 	ErrOrderCannotReceive    = errors.New("order cannot receive")
+	ErrOrderCannotReturn     = errors.New("order cannot return")
+	ErrOrderCannotComplete   = errors.New("order cannot complete")
 	ErrPermissionDenied      = errors.New("permission denied")
 )
 
@@ -62,6 +64,23 @@ func (s *Service) HandoffRecords(userID uint64, orderID uint64) ([]HandoffRecord
 	return s.repo.HandoffRecords(userID, orderID)
 }
 
+func (s *Service) SubmitReturn(userID uint64, orderID uint64, req SubmitReturnRequest) (*HandoffRecordDTO, error) {
+	if s.repo == nil {
+		return nil, ErrDependencyUnavailable
+	}
+	if orderID == 0 || req.Content == "" {
+		return nil, ErrOrderCannotReturn
+	}
+	return s.repo.SubmitReturn(userID, orderID, req)
+}
+
+func (s *Service) ConfirmReturn(userID uint64, orderID uint64) error {
+	if s.repo == nil {
+		return ErrDependencyUnavailable
+	}
+	return s.repo.ConfirmReturn(userID, orderID)
+}
+
 func (s *Service) ListForUser(userID uint64) ([]OrderDTO, error) {
 	if s.repo == nil {
 		return nil, ErrDependencyUnavailable