Thank you! I got a couple minutes in and was confused as hell. There is no reason to do the builds in the container.
Even at work, I have a few projects where we had to build a Java uber jar (all the dependencies bundled into one big far) and when we need it containerized we just copy the jar in.
I honestly don't see much reason to do builds in the container unless there is some limitation in my CICD pipeline where I don't have access to necessary build tools.
It's pretty clear that this whole project was god-tier level procrastination so I wouldn't worry too much about the details. The original stated problem could have been solved with a 5-line shell script.