### What delivering a rung costs, by bearer and direction

- **Rung price** ([extensions/rung-price.md](extensions/rung-price.md)), the record
  `wai.delivery.rung_price`: a seller's signed list of delivery prices (`wai-rung-prices`), each
  for a direction (`downlink`, `uplink`, as RFC 8506 §8.25 and §8.24 count octets), a bearer class
  (bearer-receipts §2), the regions it delivers to (a footprint of region codes), a ceiling of the
  rung's rate in bits per second, and a unit: `bytes`, `subscriber_us` or `publisher_us` on a
  two-way bearer, or `bytes_sent` or `pass_us` on a shared one, each at the divisor of the ledger
  field that bills it. Prices are in route-record's amounts, with the energy the seller states
  beside them; a figure of a class above `Estimator` names the seller's own per-hop records
  (`WMH1`) by digest, and one of a hardware class its declared uncertainty in parts per million.
  The list is a strict JSON document signed over `wai:rung-prices\x01` and named by the digest of
  its body without `sig`. A seller's latest list stands alone, and one that lapses revives none.
- **The region code** (rung-price §2): an ISO 3166-1 alpha-2 or ISO 3166-2 code in capitals, its
  country, and when a footprint *holds* it (it lists the code, or the country of a subdivision;
  never a country because it lists a subdivision of it), mapped to and from CDNI's lowercase
  codes by case alone. It is WAI's one definition, which an extension that states a region cites.
  In `wai-rs` it is the ungated `region` module, and `rung_price_verify.py` exports its Python
  twin.
- **Comparing delivery options**: a request's candidates and the limits that remove each (a `null`
  is most restrictive, units are never converted, and the least tier that covers the rung or the
  pass rate prices it); a cost and an energy per receiver, a shared transmission's divided by the
  audience the comparer states or by one; a ranking by price or by energy (a class counts only when
  the comparer is given the seller's own current per-hop records that bear the figure out and has
  confirmed the seller's key for that class; any other figure ranks as an estimate, one its own
  records contradict is set aside, and a hardware figure is compared one declared uncertainty above
  itself); each transmission's break-even audience; and the neighbour order a plan gives an asker
  of holdings §5.4, priced holders first and the unpriced after them in key order.
- **What bills each unit**: a list is a quote, billed only at a tariff the buyer signed. Room time
  is billed by a room's prices, per layer class for `subscriber_us`; downlink `bytes` by a
  delivery price per object class or a room's `bytes_out` price. A transmission's pass rate is a
  pure function of its carousel schedule; `bytes_sent` and `pass_us` are compared, and no tariff
  field bills them yet.
- **The corpus** [`live-conformance/prices/`](live-conformance/prices/): lists with a control for
  each rule, verdicts at each edge of a window, and comparisons covering every limit, decision,
  evidence verdict and energy rank, among them a calibrated label against an honest model-based
  figure. `rung_price_verify.py` is a second implementation.
