That still requires the process running the outer generator to stay active the entire time. If that fails, you can't retry from step three. You need some way of starting the outer function part way through.

You can do that manually by defining a bunch of explicit steps, their outputs and inputs, and how to transform the data around. And you could use generators to create a little DSL around that. But I think the idea here is to transform arbitrary functions into durable pipelines.

Personally, I'd prefer the more explicit DSL-based approach, but I can see why alternatives like this would appeal to some people.