[mathstuf]

They are. If you rewrite history, you get a different hash. You can do some shenanigans with git-replace, but those are usually for stitching history across gaps (like hooking pre-publish history to public release for internal archaeology at least.

What you actually want is a ban on rewriting tags or accepting branch updates to commits that do not have the current commit as an ancestor. These hooks do exist, but are not on by default (beyond the toilet paper protection of needing --force).

You also have to ban deleting branches because otherwise you just delete and push a new one with the same name. Maybe we should store topic branches in repos under refs/topics/ to distinguish integration branches from development/review branches?