Hi Zach,
I've exported and documented the variable in https://github.com/marijnh/Postmodern/commit/c7b49bd075923bc3861b15c1ae944d2... . The leading-slash thing is nice, but since support for unix sockets is currently a hack only supported on SBCL+Unix, I didn't feel comfortable integrating it too deeply into the interface.
Best, Marijn