I don't think this is taking it as far as it can go.

Everything should live in the repo. Code and docs yes. But also the planning files, epics, work items, architectural documentation and decisions. Here is a small example of my Linux system doc: https://github.com/gchamon/archie/tree/main/docs

And you don't need to reinvent the wheel. Code docs can like either right next to it in the readme or in docs/ if it's too big for a single file or the context spams multiple modules. ADRs live in docs/architecture/decisions. Epics and Workitems can also live in the docs.

Everything is for agents and everything is for humans, unless put in AGENTS.md and docs/agents or something similar, and even those are for human too.

In a nutshell, put everything in the repo, reuse standards as much as possible, the idea being it's likely the structure is already embedded in the model, and always review documentation changes.