If you haven't already, I'd seriously suggest having a look at redo (the theory but also apenwarr's implementation at https://github.com/apenwarr/redo https://g

If you haven't already, I'd seriously suggest having a look at redo (the theory but also apenwarr's implementation at https://github.com/apenwarr/redo https://github.com/apenwarr/redo). It's not going in the same direction you are exactly but building a mental model of it in my head was salutary in terms of thinking through the purpose and implementation of build tools and hopefully it'll be similarly useful to you.