Subject. A frozen implementation of true union semantics for restricted day-of-month/day-of-week cron fields under the # (nth weekday) and W (nearest weekday) special forms — a feature added to the widely-used croniter library (upstream commit pinned in harness/departments/croniter_fixtures/, MIT licensed, vendored so the refereed subject cannot drift).
Why this department exists. ROADMAP.md known gap #1: every earlier department was authored inside this repository, so "the protocol is domain-agnostic" rested on in-house evidence. This subject was born outside — a codebase this repository had never touched — and its calibration has an unusual provenance: an external referee suite was first authored blind by a party independent of the implementer, then proven against five planted mutants (5/5 caught, 2026-08-08). That external referee is not vendored here. The instruments below — oracle, claims, decoys — were re-authored by the implementing process in this repository's own format, and are accepted only because they reproduce the independent calibration's verdicts: the same five mutants, still all rejected, now through the unchanged harness/protocol.py. Who authored what: implementation and in-repo instruments by the implementer; the blind external referee and the five mutant classes by the independent party; the mutant diffs by the implementer to the independent party's specification.
The battery.
| Role | Instrument |
|---|---|
| rivals | the two semantic calibration mutants: an inverted forward combiner, and a union whose sides stay contaminated by each other's special form — same API, same claim, wrong dates |
| decoys | degenerate probe expressions (0 0 * * *), and the special forms stripped from the probes — the substance under test removed, shape kept |
| surrogates | fixed-stride and first-of-month date generators — schedules with no cron semantics |
| lesions | the other three calibration mutants as exact source patches, magnitudes measured at import as the share of a bounded behavioral fingerprint each changes |
The distinguishing reference claim is exact agreement with an independent calendar-arithmetic oracle that never calls the subject; the rejected reference claim is "accepts the API flag," true of every rival — presence of an API proves nothing about its semantics.
First command — the audit, which is parametrized over all departments:
.venv/bin/python -m pytest -q -o addopts='' tests/test_department_conformance.py tests/test_harness_croniter_department.pyHonest scope. This department measures the ingestion half of known gap #1: a foreign subject, refereed by the unchanged protocol, with independently-authored battery content. What it does not measure: adoption by an outside team — every step here was still orchestrated from this repository's own process. That axis stays open, and saying otherwise would be the exact promotion this tree exists to refuse.