We don't support docker-in-docker yet, but that's something on our short term roadmap. We have the need for this ourselves! For now, you could call a different service to spin up your sandbox with the image of your codebase. Not ideal, but this is what we do now.

Yes, you can use your own subscriptions as long as you follow their guidelines

Dagger (dagger.io) has its own container execution stack, and supports dagger-in-dagger natively, with logical scoping, and without depth limit. Would love to show you both a demo, if you're interested!

(Disclaimer, I'm the CEO of Dagger)

I founded Docker, and lack of proper nesting support was always a pet pieve of mine. I couldn't fix it in Docker, so I fixed it in Dagger instead :)