How to Debug a Synchronized Page

When someone undoes something, if you push undo, does the code undo your last action or my last action? Because obviously it's a synced page. So you would expect it to be undo your last actions. The code needs to keep track of who made what change and needs to go back in the change log rather than the general changes. And then when the live share is stopped, the collaborative sync then needs to become active. In theory, because the live share has synced both pages, it shouldn't matter which sync it's taken, because the page should be the same.