Are there any good systems that somehow enforce consistency between documentation and code? Maybe the problem is fundamentally ill-posed.

Keeping the documentation in the repo (Markdown files) and using an AI coding agent to update the code seems to work quite well for keeping documentation up to date (especially if you have an AGENTS.md/CLAUDE.md in the repo telling it to always make sure the documentation is up to date).

I am not saying it doesn't matter because it does, but how much does it matter now since we can get documentation on the fly?

I started working on something today I hadn't touched in a couple years. I asked for a summary of code structure, choices I made, why I made them, required inputs and expected outputs. Of course it wasn't perfect, but it was a very fast way to get back up to speed. Faster than picking through my old code to re-familiarize myself for sure.

Ultimately the code is the documentation.