125 reject produce glyph on multi arm effect

// Glyph discipline, produce side (dual of 400_122): `->` produces the single
// anonymous resume value. When the effect declares named resume ARMS, there is
// no anonymous value to produce — the handler must SELECT an arm with `=>`.
// Without this wall, `-> n` would emit a bare value where the synthesized
// resume union is expected and die as a raw Zig type error.
~import std/io

~pub tor request { payload: i32 }
! ask i32
    | halved i32
    | timeout
| done i32

~proc request|zig {
    const r = ask(payload);
    return switch (r) {
        .halved => |v| .{ .done = v },
        .timeout => .{ .done = -1 },
    };
}

~request(payload: 20)
! ask n -> n
| done r |> std/io:print.ln("{{ r:d }}")