fix(v2): P4 终审波——歧义渠道错误留 processing(ErrRefundRejected 哨兵)/ 拒绝fixture签名 / 错误映射测试 / GetRefund 日志

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

internal/provider/stripe/stripe.go

@@ -7,6 +7,7 @@ package stripe
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -65,6 +66,14 @@ func (p *Provider) Refund(_ context.Context, providerRef, refundID string, amoun
 	params.SetIdempotencyKey(refundID)
 	rf, err := p.sc.Refunds.New(params)
 	if err != nil {
+		// *stripe.Error + HTTPStatusCode 4xx = 渠道对这次请求的确定性拒绝(参数/状态
+		// 类错误,如金额超出可退余额、PaymentIntent 已全额退过);5xx/网络错误(err 不是
+		// *stripe.Error,或是但状态码 5xx)结果不确定,不 wrap ErrRefundRejected ——
+		// 与 alipay 同一判定原则(见 provider.ErrRefundRejected 注释 / item 1)。
+		var serr *gostripe.Error
+		if errors.As(err, &serr) && serr.HTTPStatusCode >= 400 && serr.HTTPStatusCode < 500 {
+			return "", provider.PaidFailed, fmt.Errorf("stripe: 退款被拒: %w", errors.Join(provider.ErrRefundRejected, err))
+		}
 		return "", provider.PaidFailed, fmt.Errorf("stripe: 退款请求失败: %w", err)
 	}
 	return rf.ID, mapRefundStatus(rf.Status), nil