ADR-0087 exemption (no-migration-prescription): A validity narrowing at the server's per-option gate: no key of any metadata schema is removed, renamed or re-shaped, so there is nothing for `objectstack migrate meta` to rewrite and no tombstone. What narrows is the set of writes the gate admits: a picked option whose predicate faults is refused instead of admitted. The refusal reuses the existing field-rule envelope, so no error code and no TypeScript export changes. The package publishes (not unpublished); no ADR-0087 id covers this rule and this diff adds none (not registered / already-registered).