The associated skill's shortcode, or null for a general Fate Point
usable on any skill's test. A set code is skill-specific — usable only
on that skill.
Whether charges are infinite (charges.value === null); never decremented.
The underlying Fate Mystery (opaque here; the logic in production).
Finite charges remaining (ignored when infinite).
The mystery's subtype (matched against the Fate subtype).
A normalized projection of a Fate Mystery item, decoupling the eligibility math from the live sohl.document.item.logic.MysteryLogic so it stays pure and testable. The owning logic/item is carried opaquely in ref.