I've spent the last several months watching a Claude-based agent read a production Rails codebase — opening files, tracing scopes, following background jobs, identifying the right place to investigate a bug I'd written years ago. The strange thing isn't that it works. It's how little I had to do to make it work. I went in expecting to write a lot of glue. Entity maps. Canonical module summaries. Hand-built manifests telling the model where things live. I wrote none of it. The agent reads config/routes.rb , follows the conventions Rails apps have agreed on for fifteen years, and finds what it needs. That disconnect is what this post is about. Not "AI for Rails." Rails, seen through an LLM's eyes. The agent is a new hire who reads fast The mental model that helped me most is this: the agent is a new hire on day one. It has never seen your code. It has no institutional memory. But it has general knowledge of Ruby and Rails, the way a new hire does.…