Using vdagent with x11spice is hard
We've had a few people looking for guidance on how to use the vdagent with x11spice.
It's moderately hard to do; you need to tell x11spice about a few sockets, and then run both a vdagentd and a vdagent that point to the right sockets.
There are two possible ways forward on this. One would be to revise the spicedummy.sh to have some helper functions for running vdagent. That will work reasonably well in the xinit case.
The case of xdmcp (where you want to run X and x11spice as user A, but support a logged in user B having vdagent functionality) is a good deal trickier. At the very least, you'd want to have some way of protecting a connection; the user 'B' vdagent could use an atom to get it's socket, for example. You'd also probably want to have a hand off as well; have a vdagent run by user 'A' that terminates when the one from 'B' comes on line; that way, you can resize the login screen as well as the actual session.
A much more ambitious strategy, suggested by Frediano, is to revise vd_agent itself to be available as a library. You'd still have some of the same problems, but the vdagentd code at least would be unneeded, and you could potentially simplify the code paths.