feat(v2): Stripe adapter 落地 RefundingProvider(session→payment_intent→Refunds.New,refund_id 作幂等键)

internal/provider/stripe/stripe.go

@@ -42,12 +42,45 @@ func (p *Provider) Method() string { return "stripe" }
 func (p *Provider) Capabilities() provider.Capabilities {
 	return provider.Capabilities{
 		RenderTypes:      []provider.RenderType{provider.RenderRedirect},
-		SupportsRefund:   false, // P4
+		SupportsRefund:   true, // P4:/v1/refunds
 		SettleCurrencies: []string{supportedCurrency},
 		Regions:          []string{"global"},
 	}
 }
 
+// Refund 经 Checkout Session 取 PaymentIntent 再退款。refundID 作 Idempotency-Key。
+// 不传 Stripe Reason(仅收枚举);业务文案只落 pay 本地。
+func (p *Provider) Refund(_ context.Context, providerRef, refundID string, amountMinor int64, _ string) (string, provider.PaidStatus, error) {
+	sess, err := p.sc.CheckoutSessions.Get(providerRef, nil)
+	if err != nil {
+		return "", provider.PaidFailed, fmt.Errorf("stripe: 取 session 失败: %w", err)
+	}
+	if sess.PaymentIntent == nil || sess.PaymentIntent.ID == "" {
+		return "", provider.PaidFailed, fmt.Errorf("stripe: session %s 无 payment_intent,无法退款", providerRef)
+	}
+	params := &gostripe.RefundParams{
+		PaymentIntent: gostripe.String(sess.PaymentIntent.ID),
+		Amount:        gostripe.Int64(amountMinor), // cent = USD minor,直传
+	}
+	params.SetIdempotencyKey(refundID)
+	rf, err := p.sc.Refunds.New(params)
+	if err != nil {
+		return "", provider.PaidFailed, fmt.Errorf("stripe: 退款请求失败: %w", err)
+	}
+	return rf.ID, mapRefundStatus(rf.Status), nil
+}
+
+func mapRefundStatus(s gostripe.RefundStatus) provider.PaidStatus {
+	switch s {
+	case gostripe.RefundStatusSucceeded:
+		return provider.PaidSucceeded
+	case gostripe.RefundStatusFailed, gostripe.RefundStatusCanceled:
+		return provider.PaidFailed
+	default: // pending / requires_action → 异步,交上层保持 processing
+		return provider.PaidPending
+	}
+}
+
 func (p *Provider) Create(_ context.Context, req provider.CreateRequest) (*provider.Session, error) {
 	if req.Currency != supportedCurrency {
 		return nil, fmt.Errorf("stripe: 仅支持 %s, got %s", supportedCurrency, req.Currency)