027 capture basic

// Test: Basic ~capture as top-level flow — BLOCK FORM.
//
// Ratified 2026-06-11: `capture` and `captured` take bare source blocks, no
// parens. `name { ... }` is unambiguously an invocation since `=>` took over
// branch construction (210_047). The seed block builds the cell; each
// `captured { ... }` computes the cell's NEXT value; `| captured` is the
// one-shot after-read.

~import std/io
~import std/control

~capture { total: @as(i32, 0) }
! as acc |> captured { total: acc.total + 42 }
| captured final |> std/io:print.ln("{{ final.total:d }}")