GitHub, Gitea, and Forgejo specifically store all commit hashes for PRs in the `refs/pull/` namespace. The end result is that 50 people pushing commits for six years and deleting all of their branches after squash-and-merge loses no information about how the code evolved.

The main branch remains compact with a linear history without the commit noise. Deleted branches can be restored, commits that otherwise do not exist in the history can be interacted with, and so on.