fix: tighten webhook provider resolution

backend/internal/service/payment_service.go

@@ -9,7 +9,6 @@ import (
 	"time"
 
 	dbent "github.com/Wei-Shaw/sub2api/ent"
-	"github.com/Wei-Shaw/sub2api/ent/paymentorder"
 	"github.com/Wei-Shaw/sub2api/ent/paymentproviderinstance"
 	"github.com/Wei-Shaw/sub2api/internal/payment"
 	"github.com/Wei-Shaw/sub2api/internal/payment/provider"
@@ -225,25 +224,6 @@ func (s *PaymentService) loadProviders(ctx context.Context) {
 	}
 }
 
-// GetWebhookProvider returns the provider instance that should verify a webhook.
-// It extracts out_trade_no from the raw body, looks up the order to find the
-// original provider instance, and creates a provider with that instance's credentials.
-// Falls back to the registry provider when the order cannot be found.
-func (s *PaymentService) GetWebhookProvider(ctx context.Context, providerKey, outTradeNo string) (payment.Provider, error) {
-	if outTradeNo != "" {
-		order, err := s.entClient.PaymentOrder.Query().Where(paymentorder.OutTradeNo(outTradeNo)).Only(ctx)
-		if err == nil {
-			p, pErr := s.getOrderProvider(ctx, order)
-			if pErr == nil {
-				return p, nil
-			}
-			slog.Warn("[Webhook] order provider creation failed, falling back to registry", "outTradeNo", outTradeNo, "error", pErr)
-		}
-	}
-	s.EnsureProviders(ctx)
-	return s.registry.GetProviderByKey(providerKey)
-}
-
 // --- Helpers ---
 
 func psIsRefundStatus(s string) bool {