Messenger does not handle message ID wraparound.

[lmwnshn]

Bug Report

Summary

Messenger does not handle message ID wraparound.

Solution

If you send more than uint64_t messages, the current algorithm for tracking seen messages in docs/design_messenger.md does not work. I'm guessing that the messenger should send a signal to all its connected peers, resetting their seen message counter, before allowing wraparound to occur. But I also don't think we're going to send that many messages any time soon, so we can punt on this for a while.