uBO displays it; see the screenshots above.
As far as I can tell, uBO resolves redirects and such to indicate where stuff is actually loaded from.
So you’re hiding 3rd-party resources/services behind a domain chosen to look like it’s basically 1st party? Huh.
I’m not a frontend person, but it seems possible to serve a static page that gets overwritten by loaded JS (if any), or use 1st party scripts for a minimal view, or use a 1st-party script to check wether the 3rd-party dependencies loaded, or … I don’t know, but plenty of pages manage to detect my nasty-nasty “ad blocker” and hide their content behind a veil of blur, so it seems the technical hurdles are surmountable. (Not that I want to suggest an ad-wall or anyting like that!)
Anyway, the immediate issue at hand is solved and I’m happy not having to force-reload every Discourse page. I think I also made my stance on 3rd-party dependencies in general and “reactive” websites reacting to missing ones clear. I’ll leave you mainainters to hash our whether there’s something to act on in here for you. Thanks for the help and time, and the good work in general! :wave