Dropping the pull_request gate made merge_base == HEAD a routine path rather
than a degradation, and the success line did not follow. On every push to main
the step printed "all N release heading(s) at the merge base are still present"
— a containment claim on the one event where deletion is undetectable, since
the comparison is the file against itself.
That is the dishonesty this PR fixed in the skip messages, surviving in the
success message. The line now has two forms: containment vacuous, naming
uniqueness as the half that ran, or the existing containment wording when a
real base exists. Both pinned, including that they do not collapse.
Also scopes the ci.yml negative pin to the monotonic step's own block. As a
file-wide assertion it forbade any FUTURE step in ci.yml from being
pull_request-gated and would have failed citing #133 when one legitimately was;
a companion assert keeps the extractor from silently matching nothing and
turning the negative into a tautology.
Ported from heavy-duty/box#144, where the defect was found after this PR's
approvals had landed.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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