/**
 * Next highlighted menu index: skips unselectable entries and wraps. From -1
 * (nothing highlighted yet), down lands on the first selectable entry and up
 * on the LAST — stepping up from -1 directly would land one short of it.
 * Returns `from` unchanged when nothing is selectable.
 */
export function stepIndex(selectable: boolean[], from: number, delta: 1 | -1): number {
  const count = selectable.length;
  let index = from < 0 && delta < 0 ? 0 : from;
  for (let hops = 0; hops < count; hops++) {
    index = (index + delta + count) % count;
    if (selectable[index]) return index;
  }
  return from;
}