And as I have explained in the detailed description Matthew requested,
To be clear, I was asking for details to reproduce the technical issues you're running into. I may have missed them, but I don't believe you've provided these.
our construction of the CI/CD environment is incremental, so the
assumption in the go tool code that "everything is there and it it is
not it can be downloaded directly" does not work for us
If your build system provides the Go source/packages, then Go won't try to download them directly itself. This is how Go works within Google's build system (which, again, has the same no-network-access limitation as the build system you're describing, and yet supports building Go programs/packages).
It sounds like you're having trouble with providing the Go source/packages in the format expected by cmd/go. If you would provide reproduction steps of what you're doing and the problems you're running into, we can help advise what changes you need to make, and maybe identify tooling improvements to make that easier.