Disconnect 의 진실 — `is_disconnected` 가 실제론 어떻게 동작하나

async def event_stream(req, request):
    disconnected = False
    try:
        async for chunk in adapter.stream(req.message):
            await jsonl_logger.append(req.conversation_id, chunk)
            if disconnected:
                continue  # silently consume — almost never reached
            yield f'data: {json.dumps(chunk)}\n\n'
            if await request.is_disconnected():
                disconnected = True  # also almost never reached
    except asyncio.CancelledError:
        # Starlette cancels here when the client drops.
        # JSONL is already durable up to the last successful append.
        raise

# canonical route (2026-05-07부터): 생산자와 소비자를 쪼갬.
async def event_stream():
    sse_queue: asyncio.Queue = asyncio.Queue()

    async def _pipeline():
        # adapter 호출, JSONL append, SQLite 마무리, 부수 효과 —
        # SSE 줄을 yield 하는 대신 sse_queue 에 밀어 넣음
        ...
        await sse_queue.put(None)  # 스트림 끝

    task = asyncio.create_task(_pipeline())
    app.state.background_streams.add(task)  # 서버가 추적함
    task.add_done_callback(app.state.background_streams.discard)

    try:
        while (event := await sse_queue.get()) is not None:
            yield event
    except asyncio.CancelledError:
        # 브라우저가 떠났어. 취소되는 건 이 중계뿐이고,
        # 파이프라인은 계속 돌아서 전부 착지시켜.
        raise