fix(distribution): 人工批次窗口期防退款穿透与退款中途金额单调性加固

backend/internal/modules/payment/refund_cumulative_test.go

@@ -94,3 +94,50 @@ func TestUpdateOrderRefundStatusUsesCumulativeRefundedAmount(t *testing.T) {
 		t.Fatalf("重复回调后 order.RefundAmountCent = %d, want 1000（单调不回退）", saved.RefundAmountCent)
 	}
 }
+
+// TestMarkOrderRefundingAndFailedPreserveCumulativeRefund 断言已成功退款的订单
+// 发生后续退款中或退款失败时，累计退款额不会被单笔处理金额冲减缩小。
+func TestMarkOrderRefundingAndFailedPreserveCumulativeRefund(t *testing.T) {
+	db := setupPaymentTestDB(t)
+	repo := NewRepository(db, nil, nil)
+
+	order := model.RentalOrder{
+		OrderNo: "ORD-REF-PRESERVE", ListingID: 1, AccountID: 1, OwnerID: 1, RenterID: 2,
+		Status: "completed", RentAmountCent: 10000, OwnerRentAmountCent: 6000,
+	}
+	if err := db.Create(&order).Error; err != nil {
+		t.Fatal(err)
+	}
+
+	// 先前已成功退款 5000。
+	prevRefund := model.PaymentOrder{
+		PaymentNo: "REF-PREV-1", OrderID: order.ID, OrderNo: order.OrderNo, UserID: order.RenterID,
+		Provider: "mock", ThirdOrderID: "REF-PREV-1", AmountCent: 5000, BizType: "admin_refund", Status: "refunded",
+	}
+	if err := db.Create(&prevRefund).Error; err != nil {
+		t.Fatal(err)
+	}
+
+	// 此时发起了另一笔 2000 的退款中：累计额应为 max(2000, 5000) = 5000。
+	if err := repo.markOrderRefunding(t.Context(), order.ID, 2000); err != nil {
+		t.Fatal(err)
+	}
+	var saved model.RentalOrder
+	if err := db.First(&saved, order.ID).Error; err != nil {
+		t.Fatal(err)
+	}
+	if saved.RefundStatus != "refunding" || saved.RefundAmountCent != 5000 {
+		t.Fatalf("markOrderRefunding 后状态 = %s/%d, want refunding/5000", saved.RefundStatus, saved.RefundAmountCent)
+	}
+
+	// 该笔 2000 退款最终失败：累计退款额还原为已成功流水合计 5000，而不是单笔 2000。
+	if err := repo.markOrderRefundFailed(t.Context(), order.ID, 2000); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.First(&saved, order.ID).Error; err != nil {
+		t.Fatal(err)
+	}
+	if saved.RefundStatus != "failed" || saved.RefundAmountCent != 5000 {
+		t.Fatalf("markOrderRefundFailed 后状态 = %s/%d, want failed/5000", saved.RefundStatus, saved.RefundAmountCent)
+	}
+}