---
description: TypeScript strict mode and exhaustive unions.
globs: "**/*.ts,**/*.tsx"
alwaysApply: false
---

# Strict TypeScript

- Keep `"strict": true`. Do not silence a new error with `any`.
- For a union, the default branch should assign the value to `never` so a new case breaks the build.
- Prefer a named type for a form payload over a bag of optional strings.
- Parse outside data at the boundary. Inside the app, the type should already be true.