/**
 * Format a position-recorded timestamp as a human-readable "age" string.
 *
 * - < 5 s   → "now"
 * - < 60 s  → "Ns ago"
 * - < 1 hr  → "Nm ago"
 * - else    → wall-clock time ("HH:MM")
 *
 * Used by the connection chip ("last live HH:MM") and by Phase 3.4's
 * per-device detail panel.
 */
export function formatLastSeen(ts: number, now: number = Date.now()): string {
  const ageMs = Math.max(0, now - ts);
  if (ageMs < 5_000) return 'now';
  if (ageMs < 60_000) return `${Math.floor(ageMs / 1000)}s ago`;
  if (ageMs < 60 * 60_000) return `${Math.floor(ageMs / 60_000)}m ago`;
  const d = new Date(ts);
  return d.toLocaleTimeString(undefined, { hour: '2-digit', minute: '2-digit' });
}