ADR-0087 exemption (no-migration-prescription): No authorable key is renamed, retired or re-typed: every key either block accepted by declaration still parses, and the ten gantt keys that used to ride through `.passthrough()` are now DECLARED at the types the renderer reads, so an author who wrote them keeps parsing byte-identically. The only newly refused input is a key no renderer ever read — a misspelling or an invention — for which there is no rewrite to prescribe.