Maybe forgejo has a shot?

It doesn't seem to support Mercurial though (not to imply that you were implying that it did). All I can find in this proxy/mirror thing to integrate it by presenting the Mercurial repo as a Git server: https://peterlavalle.github.io/post/forgejo-actions/

Unfortunatly out-of-the-box llm agents only focus on github support, creating friction.

So pi.dev + forgejo?