102 effect wildcard payload

// `! each *` — wildcard payload: shape-checker skips it, codegen must emit
// `fn each(item: anytype)` so Zig infers the element type. This is the
// correctness primitive that lets one generic iterator serve any element type.
~import std/io

~pub event walk { items: []const i32 }
! each *
| done usize

~proc walk|zig {
    for (items) |item| {
        each(item);
    }
    return .{ .done = items.len };
}

~walk(items: &[_]i32{ 5, 6, 7 })
! each v |> std/io:print.blk {
    v {{ v:d }}
}
| done n |> std/io:print.blk {
    count {{ n:d }}
}