/** Reactive `window.scrollY > threshold`, evaluated after mount (passive listener). */
export function useScrolledPast(threshold: number) {
  const past = ref(false);
  const on = () => (past.value = window.scrollY > threshold);

  onMounted(() => {
    on();
    window.addEventListener("scroll", on, { passive: true });
  });
  onBeforeUnmount(() => window.removeEventListener("scroll", on));

  return past;
}