What I've been learning as a 20% "harness engineer" is that in order to get the models to "learn" you need to add both documentation and static checks, as well as often custom skills. My main project at work has issues where the AI will often get super confused and step on itself trying to run tests - so the answer is writing better docs (AGENTS.md) and providing deterministic tools to work with the projects.

Large software projects (I'm thinking google3) often have large amounts of both of those things, as they're always getting new developers joining.