There seems to be a minor autocorrect issue in this article. It seems to me the example might have been intended to read "or ability" instead of "of ability"
I think I disagree with the sense that agency strictly requires an explicit belief (what's an "explicit belief" anyway?) and also I'm confused about Raemon's "Robust Agency" concept. At one point I think I understood it, but right now (the way it's defined on the Robust Agency page), I don't see how it's really any different from agency fullstop.
The description of agency here feels very "Lesswrongy", i don't think that's how most people would describe agency. I think what happened is that people got used to "robust agency" and it also changed their concept of "agency".
When people usually talk about agency i don't think they mean that in some game theoretic / decision theory sense. It's about taking initiative, acting with intention, etc.