Document or resolve SWC 'classic' runtime vs 'automatic' for React 19

[justin808]

Context

In config/swc.config.js:8-18, we use 'classic' runtime with a TODO:

// TODO: Consider switching to 'automatic' runtime when fully on React 19+
runtime: 'classic',

Questions

Since the project is already on React 19 (package.json), what's blocking the move to automatic runtime?

• Is this a React on Rails SSR compatibility issue?
• Should there be integration tests to validate this works with SSR?

Suggested Actions

1. If this is a known React on Rails limitation, link to an issue or docs
2. Add integration tests for both runtimes with SSR if feasible
3. Test automatic runtime and switch if compatible