> For decades, the way we’ve used browsers has remained linear: open a tab (or 20), search for something, read a page, repeat. It’s a model that’s worked well, but it hasn’t fundamentally changed.

Is it linear though? I think most people are using tabs the way everyone use documents. Open one, find the passage you need and keep it there. Lots of current web app makes that hard (lazy loading, memory leaks,...).

A better augmentation would be annotations. Create a new notetaking session which appears in a side bar, then either screenshot or highlight a section, then it is saved alongside the comment (and tags) and the context (link, date,..). No need for a lurking agent.

ADDENDUM

A somewhat simpler version can be found in Orgmode and Emacs. You can store link to almost anything and then the capture feature in Org mode can use them in templates.