The bookkeeper half of Fief.Key.Limbo: owns the entry map ({key_id, vnode_id, pid} per survivor), starts servers under the sibling DynamicSupervisor, and executes reap/2. A plain bookkeeper — its fate is coupled to that DynamicSupervisor under :one_for_all (see Fief.Key.Limbo), so a crash of either restarts both together and this process always comes up beside an empty child set. Its state therefore never needs reconstruction: there is nothing to rebuild.

A fief lib process: binds the instance's sim context at init and ends every handling with the :handled checkpoint (THE pattern, M3).