fix(v2): 币种错误映射 409/503(不再误导 500 重试)+ DailyLimit 量纲注释

- handler: ErrCurrencyMismatch → 409, ErrNoSettleCurrency → 503
- test: TestV2RetryCurrencyMismatch409 验证重试不同币种渠道返回 409
- config: DailyLimit 添加量纲注释(minor units)

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

config/config.go

@@ -27,10 +27,12 @@ type Config struct {
 // 只存 CredentialEnvPrefix，真值由 internal/accounts.Registry 运行时从环境变量
 // `<CredentialEnvPrefix>_<KEY>` 读取。
 type AccountConfig struct {
-	AccountID           string `mapstructure:"account_id"`
-	Channel             string `mapstructure:"channel"`
-	Weight              int    `mapstructure:"weight"`
-	Enabled             bool   `mapstructure:"enabled"`
+	AccountID string `mapstructure:"account_id"`
+	Channel   string `mapstructure:"channel"`
+	Weight    int    `mapstructure:"weight"`
+	Enabled   bool   `mapstructure:"enabled"`
+	// DailyLimit 单位为该账户所属渠道结算币种的最小单位(minor units)——渠道币种由 Capabilities().SettleCurrencies[0] 决定;
+	// 跨币种账户的限额刻度互不可比,运营配置时按各自币种填。
 	DailyLimit          int64  `mapstructure:"daily_limit"`
 	Region              string `mapstructure:"region"`
 	Subject             string `mapstructure:"subject"`

internal/handler/gateway.go

@@ -154,6 +154,10 @@ func (h *GatewayHandler) writeCreateErr(c *gin.Context, action, method string, e
 		util.RespondError(c, http.StatusBadRequest, "unknown_method", "不支持的支付方式")
 	case errors.Is(err, gateway.ErrNoAccount):
 		util.RespondError(c, http.StatusServiceUnavailable, "no_account", "该支付方式暂不可用")
+	case errors.Is(err, gateway.ErrCurrencyMismatch):
+		util.RespondError(c, http.StatusConflict, "currency_mismatch", "该支付方式结算币种与订单不符,请换一种支付方式")
+	case errors.Is(err, gateway.ErrNoSettleCurrency):
+		util.RespondError(c, http.StatusServiceUnavailable, "no_settle_currency", "该支付方式配置不完整,暂不可用")
 	default:
 		log.Printf("[v2 order] %s失败 method=%s: %v", action, method, err)
 		util.RespondError(c, http.StatusInternalServerError, "create_failed", action+"失败,请稍后重试")

internal/handler/gateway_test.go

@@ -2,10 +2,13 @@ package handler_test
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"testing"
+	"time"
 
 	"github.com/gin-gonic/gin"
 
@@ -163,3 +166,79 @@ func TestV2CallbackMalformedBodyIs400Transient(t *testing.T) {
 		t.Fatalf("malformed body callback code=%d, want 400", w.Code)
 	}
 }
+
+// TestV2RetryCurrencyMismatch409 覆盖 review 发现:重试到结算币种不同的渠道应返回 409,
+// 不再落入默认 500,以避免客户端误以为是瞬时失败而无限重试。
+func TestV2RetryCurrencyMismatch409(t *testing.T) {
+	t.Helper()
+	gin.SetMode(gin.TestMode)
+	orders := store.NewOrderStore(model.OpenTestDB(t))
+	preg := provider.NewRegistry()
+	preg.Register(fake.New()) // method="fake", settles in "USDT"
+
+	// 构造一个只支持 EUR 的 provider
+	eurProvider := &eurFakeProvider{}
+	preg.Register(eurProvider) // method="fake_eur", settles in "EUR"
+
+	areg := accounts.New([]config.AccountConfig{
+		{AccountID: "fake-a1", Channel: "fake", Region: "global", Enabled: true, Weight: 1},
+		{AccountID: "fake-a2", Channel: "fake_eur", Region: "global", Enabled: true, Weight: 1},
+	})
+	picker := accounts.NewRouter(areg, nil, nil)
+	g := gateway.New(orders, preg, picker, oneResolver{}, nopEnqueuer{}, "global")
+	r := gin.New()
+	router.SetupV2(r, g)
+
+	// 下单(USDT 渠道)
+	w, out := do(t, r, http.MethodPost, "/api/v2/orders", map[string]any{"sku": "pro_year", "method": "fake"})
+	if w.Code != http.StatusOK {
+		t.Fatalf("create code=%d body=%v", w.Code, out)
+	}
+	orderNo := out["data"].(map[string]any)["order_no"].(string)
+
+	// 重试到 EUR 渠道 → 币种不符 → 409 currency_mismatch
+	wRetry, outRetry := do(t, r, http.MethodPost, "/api/v2/orders/"+orderNo+"/retry", map[string]any{"method": "fake_eur"})
+	if wRetry.Code != http.StatusConflict {
+		t.Fatalf("retry code=%d, want 409; body=%v", wRetry.Code, outRetry)
+	}
+	if outRetry["code"] != "currency_mismatch" {
+		t.Fatalf("retry code=%v, want currency_mismatch", outRetry["code"])
+	}
+}
+
+// eurFakeProvider 是一个测试用的 provider,仅支持 EUR。
+type eurFakeProvider struct{}
+
+func (p *eurFakeProvider) Method() string { return "fake_eur" }
+
+func (p *eurFakeProvider) Capabilities() provider.Capabilities {
+	return provider.Capabilities{
+		RenderTypes:      []provider.RenderType{provider.RenderCryptoAddress},
+		SupportsRefund:   false,
+		SettleCurrencies: []string{"EUR"},
+		Regions:          []string{"global"},
+	}
+}
+
+func (p *eurFakeProvider) Create(_ context.Context, req provider.CreateRequest) (*provider.Session, error) {
+	exp := time.Now().Add(15 * time.Minute)
+	ref := "EURK-" + req.OutTradeNo
+	return &provider.Session{
+		ProviderRef: ref,
+		RenderType:  provider.RenderCryptoAddress,
+		Payload: map[string]any{
+			"address":      "EFake" + req.Account.AccountID + req.OutTradeNo,
+			"amount_minor": req.AmountMinor,
+			"currency":     req.Currency,
+		},
+		ExpiresAt: &exp,
+	}, nil
+}
+
+func (p *eurFakeProvider) VerifyCallback(_ context.Context, in provider.CallbackInput) (*provider.PaidEvent, error) {
+	return nil, errors.New("not implemented")
+}
+
+func (p *eurFakeProvider) Query(_ context.Context, req provider.QueryRequest) (*provider.PaidEvent, error) {
+	return nil, errors.New("not implemented")
+}