docs: public List<LogSegment> trunc(int newStart) {
          if (newStart < 0) {
              throw new IllegalArgumentException("Starting index must be positive.");
          }
          while (true) {
              List<LogSegment> curr = contents.get();
              int newLength = Math.max(curr.size() - newStart, 0);
              List<LogSegment> updatedList = new ArrayList<LogSegment>(curr.subList(Math.min(newStart, curr.size() - 1),
                      curr.size()));
              if (contents.compareAndSet(curr, updatedList)) {
                  return curr.subList(0, curr.size() - newLength);
              }
          }
      }