077 effect branch optional unhandled

// Test: optional effect branch (`! ?warn`) unhandled by consumer → no-op.
//
// Producer fires `warn("ignored")` three times during the loop. Consumer
// does NOT handle `! warn` (no catch-all either). Per the doc spec,
// unhandled optional yielding branches are no-ops — the handler simply
// isn't installed in the comptime struct (or is installed as no-op),
// and the call lowers to nothing. Only the terminal `done` body should
// produce visible output.

~import std/io

~pub event maybe { count: usize }
! ?warn []const u8
| done usize

~proc maybe|zig {
    var i: usize = 0;
    while (i < count) : (i += 1) {
        warn("ignored");
    }
    return .{ .done = count };
}

~maybe(count: 3)
| done c |> std/io:print.blk {
    done {{ c:d }}
}