Nothing. Workspaces are completely broken since the introduction of Workspaces 2.0, and IMHO there is little hope that they will fix it. My project has grown to be about 50,000 lines of JS code and a single(!) file is mapped at all.
There is an (ugly) solution: install a LAMP or LEMP stack and run your site locally. I installed Bitnami's LEMP stack on Windows, and all files are mapped again when I use localhost as the server.
Michael