sS renderTelegramMsgWithTimeDiff(TelegramMsg m, TelegramMsg originalMessage) {
  if (m == null) null;
  S timeDiff = originalMessage == null ? ""
    : " [T+" + iround(toSeconds(m.date-originalMessage.date)) + "]";
  ret (m.sent ? "BOT" : "USR") + timeDiff + ": " + m.text;
}