Thanks, both! I don’t think I can stand up a star-subdomain now, unfortunately, so I think I’ll have to go with no multi-site and multiple web-frontend containers. (If I’d realised this before, I would have pushed to get a star-subdomain.)
I’d certainly love to see multi-site/subfolder support — in the (unlikely) event that I wind up with some time, I might have a look into it.