GitHub (Actions) is simply not built to support monorepos. Square peg in a round hole and all that. We've opted for using `meta` to simulate monorepos, while being able to use GitHub Actions without too much downsides.
I do wonder if this really solves the author problem because by the looks of it , you just have to run meta command and it would run over each of the sub directory. While at the same time , I think I like it because this is what I think people refer to as "modular monolith"
Combining this with nats https://nats.io/ (hey if you don't want it to be over the network , you could use nats with the memory model of your application itself to reduce any overhead) and essentially just get yourself a really modular monolith in which you can then seperate things selectively (ahem , microservices) afterwards rather easily.
Obviously this would be a real pain to implement just to fix the underlying problem, but it's an interesting (awful) solution