FWIW, I think you might be better off with immutable rows and lamport clocks.

Everything is a full new row because it is “a message” including read receipts. Some messages like read receipts just don’t render in the chat.

Edits can work the same way by rendering over a previous message, even though the local and remote DB have multiple rows for the original and edited messages.

A month of development can easily save a day of research.

I was very surprised (or perhaps disappointed is a better word) when I didn’t see Lamport, paxos or raft mentioned at all. At least crdts made an appearance, although almost in the post scriptum.