This is pretty much exactly what I was going to build. It's missing a few things, so I'll either be contributing or forking this in the future.

I'll need a way to extract data as part of the tests, like screenshots and page content. This will allow supplementing the tests with non-magnitude features, as well as add things that are a bit more deterministic. Assert that the added todo item exactly matches what was used as input data, screenshot diffs when the planner fallback came into play, execution log data, etc.

This isn't currently possible from what I can see in the docs, but maybe I'm wrong?

It'd also be ideal if it had an LLM-free executor mode to reduce costs and increase speed (caching outputs, or maybe use accessibility tree instead of VLM), and also fit requirements when the planner should not automatically kick in.