In CoCalc, I use a fourth approach that I think isn’t in your list. https://blog.cocalc.com/2018/10/11/collaborative-editing.html https://blog.cocalc.com/2018/

In CoCalc, I use a fourth approach that I think isn’t in your list. https://blog.cocalc.com/2018/10/11/collaborative-editing.html https://blog.cocalc.com/2018/10/11/collaborative-editing.htm... I don’t claim it is better than any other approach, except it is easy to understand. Also I’m not sure that it isn’t technically an extreme special case of OT.