Maybe unfair to ask you (but thanks for the helpful answers so far).

Is there a check for "this distribution comes from the official source"?

Let's say some state actor compromises taaem's desktop computer, and changes the url in the manifest to (say) https://xn--githb-bjg.com/bitwarden/clients/releases/downloa... (that's a unicode lookalike ս in there, which in github at least renders without expansion as "github.com" - HN is smart enough to expand it), or something equally nefarious. CI's not going to catch that, right? And nobody's actually paying attention to changes?