Where's the source (or the subset of the source) available? Supposedly, vscode.dev is "a lightweight version of VS Code running fully in the browser", so probably a fork? I'd like to deploy this same webapp but behind our VPN.
It's not a fork, it is the same codebase. VS Code on the desktop is an Electron app, and this is (basically) running the app as a PWA without the Electron host process or certain native extensions.
As far as I'm aware there's no official guide for self-hosting it on your own server/bring-your-own-server. But allegedly it isn't difficult and there are GitHub Issues you can search for posted by others that have or are in the process of doing it.