So not really. It's a special branch path that only exists for opening PRs, and doesn't do anything other than opening a PR. Yes, they share an object space, but so do forks in the first place, so any security issues with this flow are the same ones in the fork-PR flow.
It's still a security problem. If you put an unlocked outside door on your house and rely on the interior doors to be locked, we'd agree that's not safe, right? Or to keep it safe would require the kind of uniform attentiveness that people are generally bad at.
Folks with accounts "littered with old forks created to make PRs" may not have that kind of attentiveness.
I don't understand the analogy. What's the actual risk exposed by pushing to a magic branch path that opens a PR instead of actually creating a branch, compared to creating a fork and making a PR in that way?
> in a separate branch namespace
So not really. It's a special branch path that only exists for opening PRs, and doesn't do anything other than opening a PR. Yes, they share an object space, but so do forks in the first place, so any security issues with this flow are the same ones in the fork-PR flow.
You can check out this which covers the whole flow: https://git-repo.info/en/2020/03/agit-flow-and-git-repo/
Or for a simpler overview, look at Gitea/Forgejo's implementation: https://forgejo.org/docs/latest/user/agit-support/