Build Encapsulation

Each build step uses chroot into a temporary filesystem that exists just for that step
- Makes each step functional (well-defined inputs and outputs, no side effects) which enables caching and safe re-use
- Temporary filesystem provided through repository's NFS interface
- Provides automatic dependency detection: if a file was read, the tool depended on it, otherwise it didn't

Each build step uses chroot into a temporary filesystem that exists just for that step