I've not looked at the actual protocol, but it's not impossible. If we assume every packet contains the client's (random, generated at process start) public ke

I've not looked at the actual protocol, but it's not impossible. If we assume every packet contains the client's (random, generated at process start) public key then the server could (in theory) perform key-agreement for every packet, decrypt it and handle it. In practice, it would cache the result so that it only does one key-agreement operation per client. If the server crashes (did you have the server in mind when you said "other side"?) then it looses its cache, but the first packet that the new instance of the server sees will have the client's public key in it so it just refills its cache immediately.