static void rotateStringBuilder(StringBuilder buf, int max) ctex {
  if (buf == null) ret;
  synchronized(buf) {
    if (buf.length() <= max) ret;
    
    try {
      int newLength = max/2;
      int ofs = buf.length()-newLength;
      S newString = buf.substring(ofs);
      buf.setLength(0);
      buf.append("[...] ").append(newString);
    } catch (Exception e) {
      buf.setLength(0);
    }
    buf.trimToSize();
  }
}

Began life as a copy of #1016424