ADR-0087 exemption (no-migration-prescription): This package changes no key, value or verdict: the registration door refuses exactly what it refused before, in the same words. The narrowing it travels with is the build doors', declared on `@objectstack/spec`.

ADR-0087 exemption (no-migration-prescription): No key is added, removed or renamed, and no value a legitimate producer writes is refused: the registration is the only writer of `_packageId` (`os build` writes none, the package export strips every underscore key), and a stamp equal to the shipping package is still accepted. A foreign stamp exists only in a body somebody wrote by hand, which the registration door already refuses at boot or install; this moves the same refusal to where the body is written. A conversion could not tell a foreign stamp from an agreeing one without the owner that judges it, and the refusal names the item, both values and the remedy.