[Linux] when I add an extension or module, where does it go?

When I import a new module extension, VASSAL yanks them from their original location on my disk and shuffles them off to… ____ ?

I see I have a .VASSAL directory, but there aren’t any obvious files in there besides a bajillion tiles with hashed names.

On my system, it creates an extension folder in the same directory as the module, using the name (full module name)_ext