018 store declared key addressing

// ASPIRATION — TODO idea pin. O2 (RULED 2026-07-04): one lvalue path
// grammar, four addressing heads — (3) declared keys: a field marked key
// at create is addressable as `pool[id: 7].hp`, and the index it needs is
// a DECLARED cost. `key:` marking spelling PROVISIONAL (candidate: an
// invocation-arg directive per ruling 8).
//
// THE CREDITOR — koru-examples/downloads. It runs today with a linear key scan
// standing in for this head: an inner `! sweep x when x.idx == pr.index` nested
// inside the batch sweep, purely to reach the one row a `! progress` names.
// Three transfers make it cheap and it reads like a workaround because it is
// one. The scan is the shape this pin retires.
//
// Reaching for a POSITION instead is not the shortcut it looks like: the row
// ordinal is not identity under swap-remove, and a stored position loses its
// write silently across a removal (690_092, measured). A declared key is the
// identity that survives, which is why this head and that defect are one piece
// of work.

import std/io
import std/store

std/store:new(pool, key: id, capacity: 64) { id: i64, hp: i64 }

std/store:insert(pool) { id: 7, hp: 50 }
| row _ |> std/store:stored { pool[id: 7].hp: pool[id: 7].hp - 10 }
    |> std/io:print.ln("hp {{ pool[id: 7].hp:d }}")