> I would actually be keen for something similar that is both open-source and totally local

Did you actually look at it? Or just look at it? Because it is actually open-source and totally local.

    # ... nonsense
    while true; do
      grim - | tee ~/.recall/$(date "+%Y-%m-%dT%H-%M-%S").png | tesseract stdin stdout 2>/dev/null >~/.recall/$(date "+%Y-%m-%dT%H-%M-%S").log
      # ... other nonsense
    done

I think all the nonsense/emojis are supposed to be funny, but that actually does the thing. Replace "tesseract" with whatever local AI you want; replace grim with some other screenshotting tool if you like.

I've done something like this for over a decade (although I have a diff that deletes duplicate frames) and I like to partition by date (do that "T" becomes a "/") because that makes other things easier, but my script isn't much more complicated than that.