Pricing occupancy: the open core

Whether state occupancy is priced by recurring rent or by refundable deposit is open, and the two are genuinely different: a deposit is refundable and locks capital; rent is recurring and recycles abandoned state. Both have live precedent. Ergo runs recurring rent [S]. Cardano prices state with a refundable minimum value per unit of state, scaled by size through a protocol parameter [S].

The recommended state model constrains this choice in a way worth stating plainly. In that model, consuming a unit of state leaves a permanent marker in an append-only set that never shrinks [S]. A marker has no owner and holds nothing, so recurring rent cannot reach it, and the fastest-growing component of state is unpriceable by rent [A]. Permanent state must therefore be priced once, at the moment of its creation, as a component of the transaction fee, whatever recurring mechanism applies to active state [A]. The consequence is that the choice of state commitment structure and the fee model are one decision taken in two places, and both are open.

Two further open items are cheap to settle now and expensive to discover later. In the recommended model a unit of state carries one quantity of one asset [S], so the arrangement where every unit of state carries enough of the fee asset to pay its own rent, which is how Ergo's boxes work, is not directly expressible; it needs either an added field on the state unit or a paired fee-bearing record, and neither choice is obvious [A]. And calibration: the precedent says get the mechanism right at genesis and leave the magnitude adjustable. Ergo shipped rent at launch, still needed a supermajority soft fork to extend rewards after emission ended, and made its storage-fee factor a parameter adjustable by on-chain vote [S]; a votable magnitude is the difference between fixing a wrong number by vote and fixing it by fork [A].