refactor(gateway): snapshot usage worker inputs

backend/internal/handler/openai_gateway_handler.go

@@ -1379,6 +1379,7 @@ func (h *OpenAIGatewayHandler) ResponsesWebSocket(c *gin.Context) {
 			zap.Int("candidate_count", scheduleDecision.CandidateCount),
 		)
 
+		var requestPayloadHash string
 		hooks := &service.OpenAIWSIngressHooks{
 			InitialRequestModel: reqModel,
 			BeforeRequest: func(turn int, payload []byte, originalModel string) error {
@@ -1464,7 +1465,7 @@ func (h *OpenAIGatewayHandler) ResponsesWebSocket(c *gin.Context) {
 						UpstreamEndpoint:   upstreamEndpoint,
 						UserAgent:          userAgent,
 						IPAddress:          clientIP,
-						RequestPayloadHash: service.HashUsageRequestPayload(firstMessage),
+						RequestPayloadHash: requestPayloadHash,
 						APIKeyService:      h.apiKeyService,
 						ChannelUsageFields: channelMappingWS.ToUsageFields(reqModel, result.UpstreamModel),
 					}); err != nil {
@@ -1484,6 +1485,9 @@ func (h *OpenAIGatewayHandler) ResponsesWebSocket(c *gin.Context) {
 			wsFirstMessage = h.gatewayService.ReplaceModelInBody(firstMessage, channelMappingWS.MappedModel)
 		}
 
+		// WebSocket 首包可能很大，hash 必须在 hooks 外算成字符串，避免 AfterTurn 闭包保活请求体。
+		requestPayloadHash = service.HashUsageRequestPayload(wsFirstMessage)
+
 		if err := h.gatewayService.ProxyResponsesWebSocketFromClient(ctx, c, wsConn, account, token, wsFirstMessage, hooks); err != nil {
 			var failoverErr *service.UpstreamFailoverError
 			if errors.As(err, &failoverErr) {