feat(v2): 多币种 product(ProductPrice 分币价目 + v1 元回退)+ 结算币种由渠道能力驱动

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nMthbVEmQquxBRKb9Fj8u

internal/gateway/gateway.go

@@ -18,15 +18,18 @@ import (
 )
 
 var (
-	ErrProductNotFound = errors.New("gateway: product not found")
-	ErrNoAccount       = errors.New("gateway: no enabled account for method/region")
-	ErrOrderNotPending = errors.New("gateway: order not pending")
+	ErrProductNotFound  = errors.New("gateway: product not found")
+	ErrNoAccount        = errors.New("gateway: no enabled account for method/region")
+	ErrOrderNotPending  = errors.New("gateway: order not pending")
+	ErrNoSettleCurrency = errors.New("gateway: channel has no settle currency")
+	ErrCurrencyMismatch = errors.New("gateway: retry method settles a different currency")
 )
 
-// ProductResolver maps a client-facing SKU to the authoritative amount/currency.
-// Amount authority lives in pay (设计 §3.1); the client never sends raw amounts.
+// ProductResolver maps a client SKU + settlement currency to authoritative amount.
+// Currency is chosen by the selected channel's SettleCurrencies (设计 §3.1/§4.1),
+// never sent by the client.
 type ProductResolver interface {
-	Resolve(sku string) (amountMinor int64, currency, subject, bizCode string, err error)
+	Resolve(sku, currency string) (amountMinor int64, subject, bizCode string, err error)
 }
 
 // WebhookEnqueuer receives a domain payload to deliver to the business system.
@@ -72,14 +75,19 @@ type OrderResult struct {
 // account, persists a pending Order + Attempt (P1 OrderStore), and returns the
 // payment session {render_type, payload}. 加渠道不改 client(设计 §4.2)。
 func (g *Gateway) CreateOrder(ctx context.Context, in CreateOrderInput) (*OrderResult, error) {
-	amountMinor, currency, subject, bizCode, err := g.products.Resolve(in.SKU)
-	if err != nil {
-		return nil, err // ErrProductNotFound
-	}
 	prov, err := g.providers.Get(in.Method)
 	if err != nil {
 		return nil, err // ErrUnknownMethod
 	}
+	caps := prov.Capabilities()
+	if len(caps.SettleCurrencies) == 0 {
+		return nil, ErrNoSettleCurrency
+	}
+	currency := caps.SettleCurrencies[0] // 结算币种由渠道自述能力驱动(设计 §4.1)
+	amountMinor, subject, bizCode, err := g.products.Resolve(in.SKU, currency)
+	if err != nil {
+		return nil, err // ErrProductNotFound(含"该币种无价")
+	}
 	outNo := util.NewOutTradeNo("pay")
 	acct, err := g.picker.Pick(in.Method, g.region, accounts.PickHint{
 		OutTradeNo: outNo, AmountMinor: amountMinor,
@@ -154,6 +162,11 @@ func (g *Gateway) RetryOrder(ctx context.Context, outTradeNo, method string) (*O
 	if err != nil {
 		return nil, err
 	}
+	caps := prov.Capabilities()
+	if len(caps.SettleCurrencies) == 0 || caps.SettleCurrencies[0] != o.Currency {
+		// 换到结算币种不同的渠道重试 = 需重定价,超出 P3 范围(P5 多币种路由)。
+		return nil, ErrCurrencyMismatch
+	}
 	tried, err := g.orders.AttemptAccountIDs(outTradeNo, method)
 	if err != nil {
 		return nil, err