The tool you use to interact with the code database keeps track of the changes in an append-only log - if you're familiar with git, the commands for tracking changes echo those of git (push, pull, merge, etc) and many of them integrate with git tooling.

The projects in a codebase can absolutely be shared and versioned as well. Here's a log of release artifacts from a library as an example: https://share.unison-lang.org/@unison/base/releases.