How to actually clear all the old versions of files while developing add-ins for Excel

Question

I'm developing an add-in for Excel (desktop and web). I have serious issues with old versions of files (manifest.xml and html and assets) being read from previous versions or from other projects I worked on before.
Recently, I tried to go through the 'geting started' tutorial, and it kept complaining that files from a previous project weren't available anymore. Assets especially stick around way after they've stopped being used, in the current and previous projects.

I've tried all the methods to clear the cache, including the 'clear cache' button, and finding and deleting folders. It does not work consistently.

I finally had to create a brand new user account in order to be able to start fresh. This is obviously a non-starter; I can't create a new user account each time I want to modify something.
This fails both on windows and mac, using node + the npm start method.

Is there a way to have add-ins use the current version of files always?