Bridge two subsystems with a per-item declaration + one unified accessor

To let a quantity live in EITHER of two subsystems (here: a private per-entity stat/attr vs a tradable shared ledger resource) without forking every call site, use a per-item declaration (a meta list like ledgered_stats:[hp]) plus ONE accessor that routes reads/writes to the right store based on the declaration. stat_value/set_stat/adjust_stat check is_ledgered(stat): if declared, read/write the ledger (so it is tradable/priced/storable and transfers conserve); else the attr (unchanged). A quantity NOT declared is byte-for-byte the private attr it always was, so the whole feature is opt-in and existing content is untouched. This let HP/mana/karma become markets iff a world says so, with death-at-zero as a separate world-law Rule run in the tick (skipping the player). Key discipline: transferability is a property of the representation — a ledgered stat can be drained/stolen/sold (conserved), a plain-attr stat cannot be transferred at all (there is no ledger to move it on) and the accessor refuses. Pattern generalizes to any place where per-item you want to choose between private and shared/tradable storage.