I noticed that a change in my theme's css required a hard refresh to appear. Indeed, whether I use the Barceloneta theme or my own, all other css resources are downloaded with a ?version= timestamp but the theme css are not. I am using the without-caching-proxy cache profile which makes it use strongCaching. That seems appropriate, and appending a version timestamp will invalidate it, but obviously we don't have that here.
So what is the intended mechanism for invalidating a cache of theme css? I have thought about trying to instead register my css as a resource bundle with a last compiled date, and maybe taking the production-css line out of manifest.cfg but that is not ideal because it would decouple the registered css from the them (assuming it even works).