// b.sx is the SHADOW author for both names, with the OPPOSITE shapes:
// `combine` is VARIADIC, `pick` is FIXED. Each `from_b_*` bare call must pack
// against b's OWN author's signature (the F1 fix) — combine sums its variadic
// pack, pick subtracts its two fixed args.
combine :: (..xs: []s64) -> s64 {
    result := 0;
    for xs (it) { result = result + it; }
    result
}
pick :: (a: s64, b: s64) -> s64 { return b - a; }
from_b_combine :: () -> s64 { return combine(1, 2, 3, 4); }
from_b_pick :: () -> s64 { return pick(2, 7); }