/** YYYY-MM-DD in local timezone (matches Usage Insights day buckets). */
export function usageLocalDateKey(timestampMs: number): string {
  const d = new Date(timestampMs);
  const y = d.getFullYear();
  const m = String(d.getMonth() + 1).padStart(2, "0");
  const day = String(d.getDate()).padStart(2, "0");
  return `${y}-${m}-${day}`;
}
