Sender_id best practice?

For sender_id what is the best practice.

Should it be a unique conversation Id, a unique user ID, or something I haven’t considered. I guess this stems from how the sender_id is used if at all? Would a conversation 5 days from now need a new sender_id or is it okay to use and the same one from a previous conversation?

I’m using a full name right now, but that doesn’t seem to be robust to collisions.

IMHO, full name is definitely a risk of collisions. Also same user could start different conversation on different device etc thus conversation should be track per session and not per conversation otherwise it will cause confusion I believe.