Thanks for the discussion Andrew.
I call it a network layer in part because that was how it was described to me, and in part because I know the client wants to make this part of their platform, and enable others to build their applications on top of it.
Right now I am in the stage where I ask around and see what others think: is there really an issue here? What is the generally known name for that problem? What have others done in this area? That's my attempt to eliminate the ignorant-experts-reinvent-the-wheel and related ignorant-experts-fight-and-churn problem.
Transactional RPC (or google tells me, TxRPC!) that's cool, I'll take a look at that and see what that brings me to. (Do you know of any open source high performance 5 nine layers?)