ADR-0087 exemption (no-migration-prescription): Nothing authorable is removed, renamed or re-shaped: `publicSharing.enabled` keeps its name, its type, its default and its accept-set, and the change is WHEN the platform holds it. There is therefore no tombstone for `objectstack migrate meta` to carry and no mechanical rewrite it could perform — a deployment whose links stop resolving must decide whether the block should be on at all, which is an authoring decision no ledger entry can make on its behalf.