One thing your tool appears to be missing (IMO) is execution sandboxing. This is useful, as you likely know, for avoiding undeclared dependencies and for avoiding dirty builds due to actions polluting the source directory, among other things. I was playing around with allowing configurable sandboxing, with symlink forest and docker as two intial options.
Very cool that you are also recognizing this issue and working on it. I sent you an email in case you want to exchange further.
[0] https://www.pantsbuild.org/stable/docs/introduction/welcome-...
https://grog.build/why-grog/