There's a cool research project https://github.com/exoharness/exo that is designed specifically as a self-modifying harness, so architecturally it separates things in a way that makes it a lot harder for the agent to break itself when modifying itself. It looks pretty neat. Saw the author do an interview on a podcast explaining it.

> does it just review sessions and rewrite markdown files

Yes, same with openclaw etc. Some might have plugins to integrate with graph or vector databases besides only markdown files.