fix(openai-ws): classify canceled client streams

backend/internal/handler/openai_gateway_handler.go

@@ -792,6 +792,22 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 			})
 		}
 		if err != nil {
+			if result != nil && result.ClientDisconnect {
+				reqLog.Info("openai.client_disconnected",
+					zap.Int64("account_id", account.ID),
+					zap.Error(err),
+				)
+				submitResponsesUsage(result)
+				return
+			}
+			if failoverClientGone(c) {
+				reqLog.Info("openai.client_disconnected",
+					zap.Int64("account_id", account.ID),
+					zap.Error(err),
+				)
+				submitResponsesUsage(result)
+				return
+			}
 			if result != nil && result.ImageCount > 0 {
 				reqLog.Warn("openai.forward_partial_error_with_image_result",
 					zap.Int64("account_id", account.ID),
@@ -3087,6 +3103,10 @@ func (h *OpenAIGatewayHandler) ensureForwardErrorResponse(c *gin.Context, stream
 	if c == nil || c.Writer == nil {
 		return false
 	}
+	if c.Request != nil && errors.Is(c.Request.Context().Err(), context.Canceled) {
+		failoverClientGone(c)
+		return false
+	}
 	// 先停 compact 心跳再读 Writer 状态，避免与心跳 goroutine 竞争。
 	compactKeepaliveCommitted := service.StopOpenAICompactSSEKeepaliveCommitted(c)
 	if compactKeepaliveCommitted {