I have two containers, the first modifies some files in the repo and the second has those files ADDed into it, locally I would map a volume on my host machine and they could both use it, is this possible in Container Builder? I am not seeing the changes the first container made in my second container.
The only directory that persists across build steps is the /workspace directory; see the documentation for further details: https://cloud.google.com/container-builder/docs/api/build-steps.