I agree that remote identity would be a poor fit, but on the other hand the caller provided a ZMTPSession when setting up the ZMTP*Codec right, so wrapping each response in a container holding a reference to that same session seems strange to me.

I would be fine with a truncated flag in ZMTPMessage, personally.

However, mostly I'm interested in getting rid of the huge delta that the that is the ZMTP/2.0 change. I have a few ideas on refactoring work I would like to propose and hear your opinions on, that can all wait until after ZMTP/2.0 is merged.