Lent twice

# One list may be lent to two parameters at once (both only read it). `pick` hands back 'b', which
# is in @x, so the result lives while 's' does (found by check claude, 2026-09-29).
fn pick [@x] [lent 'a': list[int32], lent @x 'b': list[int32]] -> lent @x list[int32] {
    return lend 'b';
}
MAIN {
    let 's': list[int32] = [1, 2];
    let 'r' := pick[lend 's', lend 's'];
    std::print.useful[list.length[lend 'r'], newln];
}