Exempt: any type not written by MessagePack's [Key]-layout formatter (own [MessagePackFormatter],
a consumer resolver, a [MessagePackObject] collection) and a type no instance of which can be
written (cultlib-gaps:ruling:slot-unmeasurable-type). The measure runs [Key] getters and a
parameterless constructor once per type per process; a failure leaves the type unchecked. The
README states the leaf exemptions and the flattenRefusedBy column.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>