feat(distribution): 补齐退款加价回退、本站自卖与开通默认规则

退款时压缩卖方加价，人工/自动批次仅完结单可入账，号主收入进主站钱包；仲裁后重算释放并支持作废未入账 DS。开通时四种模式按默认生效，对外口径合并为 35/40/25，不再单独展示通道费。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/modules/distribution/pricing.go

@@ -97,13 +97,46 @@ func DefaultRule(mode string) (Rule, error) {
 		base.DistributorARatio = DefaultReceivePercent
 		base.DistributorBRatio = DefaultSellPercent
 	case ModeSiteSelfSell:
-		return Rule{}, ErrUnsupportedMode
+		base.DistributorSellRatio = DefaultReceivePercent + DefaultSellPercent
 	default:
 		return Rule{}, ErrUnsupportedMode
 	}
 	return base, nil
 }
 
+// ValidateRule 校验模式，并在百分比服务费下要求收号+卖出+服务费合计为 100。
+func ValidateRule(rule Rule) error {
+	normalizeRulePercents(&rule)
+	if _, err := DefaultRule(rule.Mode); err != nil {
+		return ErrUnsupportedMode
+	}
+	unit := rule.ServiceFeeUnit
+	if unit == "" || unit == ServiceFeeUnitRatio {
+		unit = ServiceFeeUnitPercent
+	}
+	if unit != ServiceFeeUnitPercent && unit != ServiceFeeUnitFixedAmount {
+		return ErrInvalidServiceUnit
+	}
+	if unit != ServiceFeeUnitPercent {
+		return nil
+	}
+	var sum float64
+	switch rule.Mode {
+	case ModeTwoPartyDistributorReceive:
+		sum = rule.DistributorReceiveRatio + rule.PlatformSellRatio + rule.ServiceFeeValue
+	case ModeTwoPartyPlatformReceive:
+		sum = rule.PlatformReceiveRatio + rule.DistributorSellRatio + rule.ServiceFeeValue
+	case ModeThreeParty:
+		sum = rule.DistributorARatio + rule.DistributorBRatio + rule.ServiceFeeValue
+	case ModeSiteSelfSell:
+		sum = rule.DistributorSellRatio + rule.ServiceFeeValue
+	}
+	if math.Abs(sum-100) > 0.15 {
+		return ErrInvalidRate
+	}
+	return nil
+}
+
 // NormalizeSplitPercent 把口头 3.5/4/2.5 换成 35/40/25；已经是百分数的原样保留。
 func NormalizeSplitPercent(value float64) float64 {
 	if value <= 0 || math.IsNaN(value) || math.IsInf(value, 0) {
@@ -147,7 +180,8 @@ func CalculateSettlement(rule Rule, input SettlementInput) (SettlementResult, er
 	}
 	netPaid := input.GrossPaidAmountCent - input.RefundAmountCent
 	paymentFee := roundHalfUp(float64(netPaid) * float64(rule.PaymentFeeBPS) / 10000)
-	profit := netPaid - input.OwnerRentAmountCent - input.MarkupAmountCent
+	effectiveMarkup := EffectiveMarkupCent(netPaid, input.OwnerRentAmountCent, input.MarkupAmountCent)
+	profit := netPaid - input.OwnerRentAmountCent - effectiveMarkup
 	if profit < 0 {
 		profit = 0
 	}
@@ -164,7 +198,7 @@ func CalculateSettlement(rule Rule, input SettlementInput) (SettlementResult, er
 		NetPaidAmountCent:   netPaid,
 		PaymentFeeCent:      paymentFee,
 		ServiceFeeCent:      serviceFee,
-		MarkupAmountCent:    input.MarkupAmountCent,
+		MarkupAmountCent:    effectiveMarkup,
 		SplitBaseAmountCent: profit,
 	}
 	if rule.TaxEnabled {
@@ -206,6 +240,25 @@ func maxInt64(a, b int64) int64 {
 	return b
 }
 
+func minInt64(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+// EffectiveMarkupCent 按剩余净付款压缩加价：全额退租金后卖方不得再留加价。
+func EffectiveMarkupCent(netPaid, ownerRent, markup int64) int64 {
+	if markup <= 0 {
+		return 0
+	}
+	remain := netPaid - ownerRent
+	if remain <= 0 {
+		return 0
+	}
+	return minInt64(markup, remain)
+}
+
 // PartySplit 是一次分成拆分中单个参与方的金额。
 type PartySplit struct {
 	PartyRole  string
@@ -236,6 +289,11 @@ func SplitSettlement(rule Rule, profitCent int64, markupCent int64) []PartySplit
 			role  string
 			ratio float64
 		}{{"distributor_a", rule.DistributorARatio}, {"distributor_b", rule.DistributorBRatio}}
+	case ModeSiteSelfSell:
+		roles = []struct {
+			role  string
+			ratio float64
+		}{{"distributor_sell", rule.DistributorSellRatio}}
 	default:
 		return nil
 	}