I don’t know if “Injected” is the name of some service, or a description of what is to happen (in which case it’s lousy wording). Whatever it is, the failure mode is clearly atrocious. I hope that’s avoidable.

It's lousy wording. It means a crypto wallet extension that makes its API available to every page natively, as opposed to a web wallet that works by redirecting the user to a different page.