That is why Playwright might be a critical piece of the puzzle instead of good to have.
I have instructed agent to generate Playwright test from screenshots that will dump API calls to debug and generate mocks to trigger the edge cases bugs. I am sure if jstool is there, it can fix the bug and reload.
If you can build browser automation into jsxtool, perhaps it can replace playwright. If I remember correctly, the guys who developed puppeteer/playwright used to work for chrome devTools or something.
That's my entire thesis. I think it's a long long road. But I think you've actually done a great job of pretty much seeing the whole vision.