Ractors, Rails, and Robots: Automating the Path to Ractor-safety

Ractors are production-ready in Ruby 4.0! But the road to adopting them in Rails is long and challenging. Or is it? In this talk, we'll show how an AI agent loop helped us make rapid progress toward Rails Ractor-safety in just a couple of weeks. We'll explain why Rails' reliance on global state makes adopting Ractors hard, and why this problem is especially suited to AI-driven prototyping. Then we'll walk through the harness and specification that enabled the agent to generate, test, and refine multiple prototypes. Of course, not everything can be automated — we'll also talk about hotspots where human intervention and design is needed. We'll close with the current state of Rails Ractor-safety, what worked, what failed, and what remains.