027 obligation param qualified phantom

// Test 660_027: obligation-carrying params cross module boundaries via
// QUALIFIED phantoms — the deferred half of the 2112 borrow ruling.
//
// RULED (Lars, 2026-07-02 / refined 330_112): a user event talks about a
// foreign type's own typestate with the type qualified and the phantom bare
// — `*std/list:List_i64<!list>` consumes, `*std/list:List_i64<list!>` issues.
// The type's module colors the phantom (330_112 refuses restating it as
// `<std/list:!list>`). LINEAR TRANSFER governs pure impls: the decl is the
// contract a host proc is TRUSTED to honor (the escape hatch); a pure impl
// is CHECKED — the consumed obligation enters the body live and must be
// discharged exactly once. Here: the minimal linear passthrough, consume in
// → issue the same handle out via the branch-constructor impl (020_014's
// idiom); the caller receives the reissued obligation and frees.
//
// This is THE wall behind AoC days 7, 10, 22 (see those ledgers): without
// it, no owned collection handle can pass through any user event.
import std/io
import std/list

pub tor roundtrip { cur: *std/list:List_i64<!list> } -> *std/list:List_i64<list!>

roundtrip -> cur

std/list:new(i64)
| list xs |> roundtrip(cur: xs): ys |> std/list:len(xs: ys): n |> std/io:print.ln("len={{ n:d }}") |> std/list:free(xs: ys)
| err e |> std/io:print.ln("ERR seed {{ e:s }}")