支持结账多轮协商与按实际消耗双比例结算

允许双方最多 6 轮修改结账方案；哈夫币按实际消耗与 buyer/seller 比例计价，打超从押金扣，押金不足禁止自动完结并引导人工争议。同步收紧结账明细展示密度。

backend/internal/modules/order/checkout.go

@@ -41,10 +41,14 @@ func (r *Repository) SubmitCheckout(ctx context.Context, userID uint64, orderID
 		if err := tx.Create(&record).Error; err != nil {
 			return err
 		}
-		checkout, err := buildCheckout(order, order.RenterID, checkoutStatusSubmitted, req.Content, req.EvidenceURLS, req.ConsumableAmountCent, req.CoinConsumedM, req.OtherAmountCent, 0, false)
+		// 首轮：租客提案，轮到号主确认/还价；押金赔付可由租客申报 other
+		checkout, err := buildCheckout(order, order.RenterID, checkoutStatusSubmitted, req.Content, req.EvidenceURLS, req.ConsumableAmountCent, req.CoinConsumedM, req.OtherAmountCent, req.OtherAmountCent, true)
 		if err != nil {
 			return err
 		}
+		checkout.RoundCount = 1
+		checkout.Turn = checkoutTurnOwner
+		checkout.ProposedBy = order.RenterID
 		if err := tx.Create(&checkout).Error; err != nil {
 			return err
 		}
@@ -58,7 +62,7 @@ func (r *Repository) SubmitCheckout(ctx context.Context, userID uint64, orderID
 			UserID:  order.OwnerID,
 			Type:    "checkout",
 			Title:   "租客已发起结账",
-			Content: "请检查账号状态和消耗明细，确认无误后完成结算。",
+			Content: "请检查账号状态和消耗明细，确认无误后完成结算；也可修改后交由租客确认。",
 			BizType: "order",
 			BizID:   &orderID,
 		}); err != nil {
@@ -80,6 +84,7 @@ func (r *Repository) ConfirmReturn(ctx context.Context, userID uint64, orderID u
 	return r.ConfirmCheckout(ctx, userID, orderID)
 }
 
+// ConfirmCheckout 号主同意当前提案并完结（轮到号主时）
 func (r *Repository) ConfirmCheckout(ctx context.Context, userID uint64, orderID uint64) error {
 	var refund *refundAction
 	err := r.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
@@ -93,11 +98,14 @@ func (r *Repository) ConfirmCheckout(ctx context.Context, userID uint64, orderID
 		if order.Status != orderStatusPendingCheckoutConfirm || order.HandoffStatus != handoffStatusPendingOwnerCheckout {
 			return ErrCheckoutCannotConfirm
 		}
-		var checkout model.OrderCheckout
-		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).
-			Where("order_id = ? AND status = ?", order.ID, checkoutStatusSubmitted).
-			Order("id DESC").
-			First(&checkout).Error; err != nil {
+		checkout, err := lockOpenCheckout(tx, order.ID)
+		if err != nil {
+			return err
+		}
+		if normalizeCheckoutTurn(checkout) != checkoutTurnOwner {
+			return ErrCheckoutCannotConfirm
+		}
+		if err := ensureCheckoutCompletable(order, checkout); err != nil {
 			return err
 		}
 		now := time.Now()
@@ -108,7 +116,7 @@ func (r *Repository) ConfirmCheckout(ctx context.Context, userID uint64, orderID
 		}
 		checkout.Status = checkoutStatusAccepted
 		checkout.OwnerAdjustedAt = &now
-		action, err := r.finalizeCheckout(tx, &order, &checkout, "号主已确认结账，订单完成。")
+		action, err := r.finalizeCheckout(tx, &order, checkout, "号主已确认结账，订单完成。")
 		refund = action
 		return err
 	})
@@ -119,27 +127,42 @@ func (r *Repository) ConfirmCheckout(ctx context.Context, userID uint64, orderID
 	return nil
 }
 
+// CounterCheckout 任一方在轮到自己时修改结账提案（最多 checkoutMaxRounds 轮）
 func (r *Repository) CounterCheckout(ctx context.Context, userID uint64, orderID uint64, req CounterCheckoutRequest) (*CheckoutDTO, error) {
 	var checkoutID uint64
+	var orderSnapshot model.RentalOrder
 	err := r.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
 		var order model.RentalOrder
 		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).First(&order, orderID).Error; err != nil {
 			return err
 		}
-		if order.OwnerID != userID {
+		isOwner := order.OwnerID == userID
+		isRenter := order.RenterID == userID
+		if !isOwner && !isRenter {
 			return ErrPermissionDenied
 		}
-		if order.Status != orderStatusPendingCheckoutConfirm || order.HandoffStatus != handoffStatusPendingOwnerCheckout {
+		if order.Status != orderStatusPendingCheckoutConfirm && order.Status != orderStatusPendingCheckoutAccept {
 			return ErrCheckoutCannotCounter
 		}
-		var checkout model.OrderCheckout
-		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).
-			Where("order_id = ? AND status = ?", order.ID, checkoutStatusSubmitted).
-			Order("id DESC").
-			First(&checkout).Error; err != nil {
+		checkout, err := lockOpenCheckout(tx, order.ID)
+		if err != nil {
 			return err
 		}
-		// 号主修正只认押金赔付扣除；other 与 deduct 对齐，避免双字段语义分裂
+		turn := normalizeCheckoutTurn(checkout)
+		if isOwner && (turn != checkoutTurnOwner || order.Status != orderStatusPendingCheckoutConfirm) {
+			return ErrCheckoutCannotCounter
+		}
+		if isRenter && (turn != checkoutTurnRenter || order.Status != orderStatusPendingCheckoutAccept) {
+			return ErrCheckoutCannotCounter
+		}
+		round := checkout.RoundCount
+		if round <= 0 {
+			round = 1
+		}
+		if round >= checkoutMaxRounds {
+			return ErrCheckoutMaxRounds
+		}
+
 		depositDeductCent := req.DepositDeductAmountCent
 		if depositDeductCent <= 0 && req.OtherAmountCent > 0 {
 			depositDeductCent = req.OtherAmountCent
@@ -150,6 +173,8 @@ func (r *Repository) CounterCheckout(ctx context.Context, userID uint64, orderID
 		}
 		now := time.Now()
 		checkout.Status = checkoutStatusCountered
+		checkout.RoundCount = round + 1
+		checkout.ProposedBy = userID
 		checkout.RentAmountCent = next.RentAmountCent
 		checkout.OwnerRentAmountCent = next.OwnerRentAmountCent
 		checkout.PlatformFeeCent = next.PlatformFeeCent
@@ -160,18 +185,33 @@ func (r *Repository) CounterCheckout(ctx context.Context, userID uint64, orderID
 		checkout.DepositDeductAmountCent = next.DepositDeductAmountCent
 		checkout.RenterRefundAmountCent = next.RenterRefundAmountCent
 		checkout.OwnerIncomeAmountCent = next.OwnerIncomeAmountCent
+		checkout.ShortfallCent = next.ShortfallCent
+		checkout.OvershootAmountCent = next.OvershootAmountCent
 		checkout.OwnerAdjustmentReason = req.Reason
 		checkout.OwnerAdjustedAt = &now
 		checkout.EvidenceURLS = next.EvidenceURLS
-		order.Status = orderStatusPendingCheckoutAccept
-		order.HandoffStatus = handoffStatusPendingRenterCheckout
+
+		notifyUserID := order.RenterID
+		notifyTitle := "号主已修改结账金额"
+		notifyContent := "请核对对方修正的消耗和结算金额。可同意完结、继续还价（最多 6 轮），或发起争议。"
+		if isOwner {
+			checkout.Turn = checkoutTurnRenter
+			order.Status = orderStatusPendingCheckoutAccept
+			order.HandoffStatus = handoffStatusPendingRenterCheckout
+		} else {
+			checkout.Turn = checkoutTurnOwner
+			order.Status = orderStatusPendingCheckoutConfirm
+			order.HandoffStatus = handoffStatusPendingOwnerCheckout
+			notifyUserID = order.OwnerID
+			notifyTitle = "租客已修改结账金额"
+		}
 		order.SettlementStatus = settlementStatusPending
 		orderID := order.ID
 		if err := notification.Append(tx, notification.Entry{
-			UserID:  order.RenterID,
+			UserID:  notifyUserID,
 			Type:    "checkout",
-			Title:   "号主已修改结账金额",
-			Content: "请核对号主修正的消耗和结算金额。同意后订单完成；不同意可发起争议。",
+			Title:   notifyTitle,
+			Content: notifyContent,
 			BizType: "order",
 			BizID:   &orderID,
 		}); err != nil {
@@ -180,10 +220,11 @@ func (r *Repository) CounterCheckout(ctx context.Context, userID uint64, orderID
 		if err := tx.Save(&order).Error; err != nil {
 			return err
 		}
-		if err := tx.Save(&checkout).Error; err != nil {
+		if err := tx.Save(checkout).Error; err != nil {
 			return err
 		}
 		checkoutID = checkout.ID
+		orderSnapshot = order
 		return nil
 	})
 	if err != nil {
@@ -193,15 +234,11 @@ func (r *Repository) CounterCheckout(ctx context.Context, userID uint64, orderID
 	if err != nil {
 		return nil, err
 	}
-	dto := toCheckoutDTOForUser(*checkout, userID, model.RentalOrder{
-		OwnerID:             userID,
-		RentAmountCent:      checkout.RentAmountCent,
-		OwnerRentAmountCent: checkout.OwnerRentAmountCent,
-		DepositAmountCent:   checkout.DepositAmountCent,
-	})
+	dto := toCheckoutDTOForUser(*checkout, userID, orderSnapshot)
 	return &dto, nil
 }
 
+// AcceptCheckout 租客同意当前提案并完结（轮到租客时）
 func (r *Repository) AcceptCheckout(ctx context.Context, userID uint64, orderID uint64) error {
 	var refund *refundAction
 	err := r.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
@@ -215,17 +252,20 @@ func (r *Repository) AcceptCheckout(ctx context.Context, userID uint64, orderID
 		if order.Status != orderStatusPendingCheckoutAccept || order.HandoffStatus != handoffStatusPendingRenterCheckout {
 			return ErrCheckoutCannotConfirm
 		}
-		var checkout model.OrderCheckout
-		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).
-			Where("order_id = ? AND status = ?", order.ID, checkoutStatusCountered).
-			Order("id DESC").
-			First(&checkout).Error; err != nil {
+		checkout, err := lockOpenCheckout(tx, order.ID)
+		if err != nil {
+			return err
+		}
+		if normalizeCheckoutTurn(checkout) != checkoutTurnRenter {
+			return ErrCheckoutCannotConfirm
+		}
+		if err := ensureCheckoutCompletable(order, checkout); err != nil {
 			return err
 		}
 		now := time.Now()
 		checkout.Status = checkoutStatusAccepted
 		checkout.RenterConfirmedAt = &now
-		action, err := r.finalizeCheckout(tx, &order, &checkout, "租客已确认修正结账，订单完成。")
+		action, err := r.finalizeCheckout(tx, &order, checkout, "租客已确认结账协商，订单完成。")
 		refund = action
 		return err
 	})
@@ -235,3 +275,42 @@ func (r *Repository) AcceptCheckout(ctx context.Context, userID uint64, orderID
 	r.startRefundBestEffort(ctx, refund)
 	return nil
 }
+
+func lockOpenCheckout(tx *gorm.DB, orderID uint64) (*model.OrderCheckout, error) {
+	var checkout model.OrderCheckout
+	err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).
+		Where("order_id = ? AND status IN ?", orderID, []string{checkoutStatusSubmitted, checkoutStatusCountered}).
+		Order("id DESC").
+		First(&checkout).Error
+	if err != nil {
+		return nil, err
+	}
+	return &checkout, nil
+}
+
+func normalizeCheckoutTurn(checkout *model.OrderCheckout) string {
+	if checkout == nil {
+		return checkoutTurnOwner
+	}
+	switch checkout.Turn {
+	case checkoutTurnOwner, checkoutTurnRenter:
+		return checkout.Turn
+	default:
+		// 兼容旧数据：已反价默认等租客，否则等号主
+		if checkout.Status == checkoutStatusCountered {
+			return checkoutTurnRenter
+		}
+		return checkoutTurnOwner
+	}
+}
+
+func ensureCheckoutCompletable(order model.RentalOrder, checkout *model.OrderCheckout) error {
+	if checkout == nil {
+		return ErrCheckoutCannotConfirm
+	}
+	settlement := buildCheckoutSettlement(order, checkout)
+	if settlement.ShortfallCent > 0 {
+		return ErrCheckoutDepositShortfall
+	}
+	return nil
+}