diff --git a/backend/internal/service/openai_gateway_response_flush_test.go b/backend/internal/service/openai_gateway_response_flush_test.go
index 2c35374596..ebfa0f22f1 100644
--- a/backend/internal/service/openai_gateway_response_flush_test.go
+++ b/backend/internal/service/openai_gateway_response_flush_test.go
@@ -387,13 +387,30 @@ func TestOpenAIResponseFlush_FailedAndErrorEventsFlushAtBoundaries(t *testing.T)
 		require.Contains(t, flushes[1], "response.failed")
 	})
 
-	t.Run("error event", func(t *testing.T) {
+	t.Run("retryable error event buffered until terminal", func(t *testing.T) {
+		// 可重试类 error 帧不算客户端输出：保持在 attempt 缓冲中不单独 flush，
+		// 为随后可能到达的 response.failed 保留 pre-output failover 能力，
+		// 与终止帧一起出站。
 		body := "data: {\"type\":\"error\",\"error\":{\"message\":\"failed\"}}\n\n" +
 			"data: [DONE]\n\n"
 		recorder := newOpenAIResponseFlushRecorder()
 
 		result, err := runOpenAIResponseFlushTest(recorder, io.NopCloser(strings.NewReader(body)), config.GatewayConfig{})
 
+		require.NoError(t, err)
+		require.NotNil(t, result)
+		gotBody, flushes := recorder.snapshot()
+		require.Equal(t, body, gotBody)
+		require.Len(t, flushes, 1)
+	})
+
+	t.Run("non-retryable error event flushes at boundary", func(t *testing.T) {
+		body := "data: {\"type\":\"error\",\"error\":{\"code\":\"invalid_request\",\"message\":\"bad request\"}}\n\n" +
+			"data: [DONE]\n\n"
+		recorder := newOpenAIResponseFlushRecorder()
+
+		result, err := runOpenAIResponseFlushTest(recorder, io.NopCloser(strings.NewReader(body)), config.GatewayConfig{})
+
 		require.NoError(t, err)
 		require.NotNil(t, result)
 		gotBody, flushes := recorder.snapshot()