shadcn/ui makes Base UI the default, ships migration as agent skill

shadcn/ui switched the default primitive layer for new projects from Radix to Base UI, per the project's changelog. Radix isn't deprecated. Existing projects keep working. Nothing forces an upgrade.

What's worth stopping on isn't the default swap, it's how they built the on-ramp. Instead of a codemod script you run once and hope, shadcn/ui shipped a skill that coding agents execute directly: migrate one component, report what changed, move to the next, and if something breaks, roll back on the git branch. Component-by-component, not repo-wide-and-pray.

That's a real difference from how breaking changes have shipped for a decade. A codemod is a static transform: it rewrites syntax and hopes your code fits the pattern it anticipated. An agent running a skill can look at what it just changed, decide if it's still broken, and try a different approach before moving on. The rollback is scoped to the component, not the whole migration.

I maintain a few libraries where I've dreaded a breaking change for exactly this reason. A codemod that touches 200 files and fails on 12 of them means you're now debugging someone else's regex logic at 11pm. A skill that migrates one component, checks its own work, and reports status per file is a fundamentally safer default, especially for anything using Radix's compound-component patterns where the API surface is deep.

The thing to watch: whether other component libraries (Radix itself, Headless UI, React Aria) start shipping their own migration skills instead of codemods. If shadcn/ui's approach works cleanly in practice, it becomes the reference implementation every maintainer copies rather than something unique to shadcn.