export const formatRelativeTime = (timestampMs: number, nowMs: number): string => {
  if (!timestampMs) return '';
  const diff = Math.max(0, nowMs - timestampMs);
  const s = Math.floor(diff / 1000);
  if (s < 60) return 'just now';
  const m = Math.floor(s / 60);
  if (m < 60) return `${m}m ago`;
  const h = Math.floor(m / 60);
  if (h < 24) return `${h}h ago`;
  const d = Math.floor(h / 24);
  if (d < 7) return `${d}d ago`;
  // Spencer, 2026-09-10, looking at a thread list where one row read `5/29/2026` between two
  // that read `4d ago`: *"why does receptionist one have a date of 5/29/2026 instead of following the
  // Xd/Xw/Xy format the others follow?"*
  //
  // A DATE IN A COLUMN OF AGES IS A DIFFERENT QUESTION ANSWERED. Every other row says how long ago;
  // that one said when, and the reader has to do the subtraction themselves to compare it with the row
  // above it. The fallback was there because a week felt like the end of usefully-relative time. It is
  // not: a thread list is sorted by recency, so `15w ago` places a row against its neighbours
  // instantly and a date does not.
  //
  // WEEKS THEN YEARS, WITH NO MONTHS, because those are the three units named. A month is not a
  // fixed number of days and picking one silently makes `4w` and `1mo` disagree about the same
  // instant; if months are wanted they are a decision, not an omission.
  const w = Math.floor(d / 7);
  if (w < 52) return `${w}w ago`;
  return `${Math.floor(d / 365)}y ago`;
};