c569ece7

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Grandfather flag skips per-change round-trip too, not just idempotence

The grandfather flag previously only skipped the per-change idempotence
check. But the round-trip check is just as much an end-state invariant
that legacy scripts aren't expected to satisfy in isolation — e.g.
revert scripts that recreate a table via a "_new" swap leave the
primary-key index with a different name than the original deploy, so
revert+redeploy lands at a structurally different schema even though
the columns match.

Now stepIsGrandfathered skips both checks. The whole-plan cycle and
schema-equality checks still apply to grandfathered steps end-to-end,
so the end-state invariants are not lost.

Fixture: toy-sqitch-grandfathered gains an add-shape change whose
revert uses the swap-via-_new pattern, making round-trip catch the
index-name asymmetry. The "with grandfather tag" test confirms it's
skipped; the "without grandfather tag" test confirms it would fire.

Module and field docs updated.

Timeline