major introduced by this diff in .changeset/22130-protocol-18.md: @objectstack/spec

ADR-0087 exemption (already-registered): The protocol major moves, and that move publishes the already-registered step-18 chain as the current upgrade path: these are its 64 D2 conversions, which `os migrate meta --from 17` replays together with the step's 329 D3 semantic entries. Each entry was registered by the change that made its break, under that change's own disposition; this diff adds, renames and removes none. The one edit outside that chain is the manifest's `engines.protocol` range: it is the ADR-0087 D1 handshake's input rather than a metadata shape any conversion rewrites, and `os migrate meta --write` rewrites it from `'^17'` to `'^18'`. The other categories are closed on facts: the package publishes (not unpublished); a consumer has an edit to make (not no-migration-prescription); and an exported value and the load door move, not a TypeScript declaration alone (not runtime-interface-only or type-surface-only).