013 js continuation branch dispatch

// NOTE: narrowed to Zig — print.ln of a bare variable WITH newline has no JS
// variant yet (print.ln is a Zig comptime transform; std/io:print has |js but no
// newline). print.ln cross-target JS for variable args is a tracked gap.
// JS continuation-branch dispatch: the JS emitter switches on the returned
// branch tag (as Zig does), firing only the matched branch — not all of them.
// n=4 → only the `even` branch fires; byte-identical on both targets. Minimal,
// no std/args dependency.
~import std/io

~tor pick { n: i32 }
| even string
| odd string

~proc pick|zig {
    if (@mod(n, 2) == 0) {
        return .{ .even = "even" };
    }
    return .{ .odd = "odd" };
}

~proc pick|js {
    if (n % 2 === 0) {
        return { tag: "even", even: "even" };
    }
    return { tag: "odd", odd: "odd" };
}

~pick(n: 4)
| even e |> std/io:print.ln(e)
| odd o |> std/io:print.ln(o)