Re-copied from the Template canonical (its d04fa82). This project's copy was
byte-identical to the canonical's 2026-09-02 state and carried none of four
fixes made since. It gates every guard here, so a wrong verdict from it is a
wrong verdict about everything it was ever pointed at.
**The one that matters most: it never checked the baseline.** It mutated, ran
the command once, and called any red a catch — so a suite already failing for
an UNRELATED reason printed "prove-guard: good — the guard caught it, and only
it" and exit 0 for an assertion nobody had written. GUARDS.md §1's own recipe
carries the missing step and the script had dropped it: restore, run again,
expect green again. Now exit 2, because an unusable baseline is "did not run".
Also: a `__pycache__` purge, because CPython invalidates a `.pyc` on mtime in
whole seconds and size, so a same-length mutation survived the restore and the
run reported the guard green. And two runner summary formats it could not read,
each falling through to an approximate line count that is not conservative —
one of them made a correct guard reddening exactly one test always exit 3,
telling its author to narrow a guard that was already narrow.
The header now also states that it edits the working tree, which matters on any
host where something renders or deploys from the checkout on a schedule.
Previous copy kept beside it as prove-guard.sh.bak-20260910.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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