The action-exercise job commits a scratch base, marks it as an in-job
fixture branch, commits an insert-above edit, and runs the composite
action against that history — proving the wiring AND a genuine
merge-base comparison, not just an action.yml parse. Base ref passed
explicitly: the shallow PR checkout has no origin/main to resolve.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Every case from #6's test list: the documented-flow passes (insert-above,
the stamp, prose-only), the box#122 deletion shape, the box#118 duplicate
(proven to run before every history gate, the box#143 ordering), rc
distinctness, both STRICT degradations, the file-first-added edge, the
vacuous push-to-main shape, and the action's env wiring.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Port of box's changelog-monotonic.sh (box#122, caught in review of
box#118) as a composite action, folding in cast's port notes (cast#133).
Uniqueness on HEAD runs before anything that needs history (box#143);
containment degrades loudly, and the action defaults strict to 1 so CI
can never take the skip path.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
