feat(v2): gateway.Refund 编排(部分/多次累计 + 超退守卫 + crypto 人工向闭环)+ RefundingProvider 加 refundID 幂等键

internal/provider/fake/fake.go

@@ -20,6 +20,11 @@ import (
 type Provider struct {
 	mu           sync.Mutex
 	queryResults map[string]provider.PaidEvent
+
+	supportsRefund bool
+	refundRef      string
+	refundStatus   provider.PaidStatus
+	refundErr      error
 }
 
 func New() *Provider { return &Provider{queryResults: map[string]provider.PaidEvent{}} }
@@ -29,7 +34,7 @@ func (p *Provider) Method() string { return "fake" }
 func (p *Provider) Capabilities() provider.Capabilities {
 	return provider.Capabilities{
 		RenderTypes:      []provider.RenderType{provider.RenderCryptoAddress},
-		SupportsRefund:   false,
+		SupportsRefund:   p.supportsRefund,
 		SettleCurrencies: []string{"USDT"},
 		Regions:          []string{"global"},
 	}
@@ -89,3 +94,23 @@ func (p *Provider) SetQueryResult(providerRef string, ev provider.PaidEvent) {
 	defer p.mu.Unlock()
 	p.queryResults[providerRef] = ev
 }
+
+// EnableRefund 令 fake 表现为可退渠道并预置一次退款结果(测试缝)。
+func (p *Provider) EnableRefund(refundRef string, status provider.PaidStatus, err error) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.supportsRefund = true
+	p.refundRef = refundRef
+	p.refundStatus = status
+	p.refundErr = err
+}
+
+// Refund implements provider.RefundingProvider (测试缝:忽略入参,回放预置结果)。
+func (p *Provider) Refund(_ context.Context, _, _ string, _ int64, _ string) (string, provider.PaidStatus, error) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if p.refundErr != nil {
+		return "", provider.PaidFailed, p.refundErr
+	}
+	return p.refundRef, p.refundStatus, nil
+}