This is the thread's initial revision.
Typos/mistakes
Are the "naunces" and "nuances" generally supposed to be nonces? Is it an alternative spelling I have not encountered?
Should the keyid/sid be included in the plaintext part of the message? Why not inside the encryption? I would assume that some sort of session information would be available as part of the chat transport, and thus should not have to be a part of the plaintext. Am I missing something?
Transcript transport assumtion
To me is a rather rash assumption to make - that the underlying transport can be relied on to deliver messages in the exact same order. In XMPP this is generally the case, but I would assume that the aspiration is for this protocol to be used also for other underlying protocols, such as IRC and Bonjour/Avahi based mesh chat, which as far as I know provide nothing of the sort. What would the potential consequences be in such circumstances? Would it be possible to reconstruct the reorderings from the recieved messages?
All in all, splendid work!