You could require orderable sequence numbers before or after each line. It would be easiest as yet another VT escape sequence, but if you are pie-in-sky adding

You could require orderable sequence numbers before or after each line. It would be easiest as yet another VT escape sequence, but if you are pie-in-sky adding more standard "files" anyway maybe you wish for lines to be newline-delimited JSON CRDTs while you are at it.