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/gateway/refund.go

@@ -3,6 +3,7 @@ package gateway
 import (
 	"context"
 	"errors"
+	"log"
 	"time"
 
 	"github.com/wangjia/pay/internal/model"
@@ -93,9 +94,20 @@ func (g *Gateway) Refund(ctx context.Context, in RefundInput) (*RefundResult, er
 	// 渠道退款:refundID 作渠道幂等键。
 	refundRef, pstatus, rerr := rp.Refund(ctx, att.ProviderRef, refundID, in.AmountMinor, in.Reason)
 	if rerr != nil {
-		_, _ = g.refunds.MarkRefundStatus(refundID, model.RefundProcessing, model.RefundFailed, "", time.Now())
-		_ = g.enqueueRefundEvent(o, att, r, "refund.failed", "")
-		return &RefundResult{RefundID: refundID, Status: string(model.RefundFailed)}, rerr
+		if errors.Is(rerr, provider.ErrRefundRejected) {
+			// 渠道明确拒绝:钱确定没退成,安全标 failed 并释放预留额度(RefundSum
+			// 守卫按 status<>failed 计,见 store.CreateRefundGuarded)。
+			_, _ = g.refunds.MarkRefundStatus(refundID, model.RefundProcessing, model.RefundFailed, "", time.Now())
+			_ = g.enqueueRefundEvent(o, att, r, "refund.failed", "")
+			return &RefundResult{RefundID: refundID, Status: string(model.RefundFailed)}, rerr
+		}
+		// 歧义渠道错误(超时/网络/5xx 等结果不确定的失败):不改状态,留 processing
+		// 继续占用预留额度——渠道那边可能已经实际执行了退款,标 failed 会在没有真退成
+		// 的情况下释放额度,让同单能再退一次造成超退,而且 P6 只扫 processing 态的
+		// RefundStuckAlertTask 对账/告警会因为状态被误标 failed 而永远扫不到它。
+		// 退款结果不确定,留 processing 待人工核实/对账收敛。
+		log.Printf("[gateway] refund %s 渠道结果不确定(非 ErrRefundRejected),留 processing 待人工/对账: %v", refundID, rerr)
+		return &RefundResult{RefundID: refundID, Status: string(model.RefundProcessing)}, rerr
 	}
 	switch pstatus {
 	case provider.PaidSucceeded: