As others have mentioned, these agentic capabilities are fully achievable within a Chrome Extension.

In fact, we built one, rtrvr.ai that has even better Web Agent performance than Open AI's Operator with human assistant and 7x faster than leading competitor: https://www.rtrvr.ai/blog/web-bench-results

Your Accessibility Tree requirement is a poor excuse, rather you should build up an agent from a first principles understanding of DOM interactions.

A browser is a SERIOUS security risk, you need a dedicated team to just pull in the latest security patches that Google pushes to Chromium or your users are sitting ducks to exploits and hacks...