/** Subtract calendar months in UTC, clamping an unavailable day to the target month's last day. */
export function calendarMonthsBefore(date: Date, months: number): Date {
  const result = new Date(date);
  const day = result.getUTCDate();
  result.setUTCDate(1);
  result.setUTCMonth(result.getUTCMonth() - months);
  const last = new Date(result);
  last.setUTCMonth(last.getUTCMonth() + 1, 0);
  result.setUTCDate(Math.min(day, last.getUTCDate()));
  return result;
}