Sure, so the first thing I would think about is the operational transform or CRDT approach. In my last role at Lumen Labs, we actually built something similar for our document collaboration feature. We ended up going with CRDTs because they handle offline scenarios better, which was important for our mobile users.

Oh yeah, there was this one really frustrating bug where... basically, when two people would type at the exact same position, like both trying to add text at the same cursor location, sometimes the order would flip after syncing. I spent like three days on it. Turned out our timestamp precision was only milliseconds and we needed microseconds. Simple fix once I found it, but finding it was a nightmare because it only happened under very specific timing conditions.