ADR-0087 exemption (no-migration-prescription): The BREAKING here is a WRITE-PATH BEHAVIOUR change, not a retirement of an authorable or published surface, so there is nothing for the ledger to carry to `objectstack migrate meta`, `spec-changes.json` or the upgrade guide: no spec property, metadata key, accepted value or exported symbol disappears, and this body prescribes no FROM/TO migration. The remedy for an affected caller is to declare the write trusted (`context.isSystem` / `runAs: 'system'`), which is application code, not a metadata migration. The obvious retirement candidate is a non-question in the same direction: `stripReadonlyForInsert` was a bare module-private `function` in `packages/metadata-protocol/src/protocol.ts`, absent from that package's `index.ts` (the only path its `exports` map offers), so no consumer could name it.