tanstack-router — Cursor rule: type-safe React routing

---
description: "Type-safe routing with TanStack Router v1 for React apps, including file-based routing, loaders, search params validation, auth guards, and TanStack Query integration"
globs: ["src/routes/**/*", "src/routeTree.gen.ts", "app.config.ts"]
alwaysApply: false
---
You are an expert in TanStack Router v1, React, TypeScript, and type-safe client-side routing.

## Core Principles
- TanStack Router is 100% type-safe — leverage TypeScript generics for params, search params, and loader data
- Prefer file-based routing with `@tanstack/router-vite-plugin` for scalability
- Always define routes with `createFileRoute` or `createRootRoute`
- Route data loading belongs in `loader` functions, not in component `useEffect`
- Search params are first-class — always define their schema with Zod for type safety

## File-Based Route Conventions
```
src/routes/
  __root.tsx          ← Root layout
  index.tsx           ← / route
  posts/
    index.tsx         ← /posts
    $postId.tsx       ← /posts/:postId (dynamic)
    _layout.tsx       ← Layout route (no path segment)
  _auth/              ← Pathless auth layout group
    dashboard.tsx
```

## Route Definition
```tsx
export const Route = createFileRoute('/posts/$postId')({
  loader: async ({ params }) => fetchPost(params.postId),
  component: PostComponent,
  errorComponent: ({ error }) => <ErrorBanner message={error.message} />,
  pendingComponent: () => <PostSkeleton />,
})

function PostComponent() {
  const post = Route.useLoaderData()     // type-safe
  const { postId } = Route.useParams()  // type-safe
  return <div>{post.title}</div>
}
```

## Type-Safe Search Params
- Always define search params with Zod and `validateSearch`
- Access with `Route.useSearch()` — never read `window.location.search` directly
```tsx
const searchSchema = z.object({
  page: z.number().int().min(1).default(1),
  q: z.string().optional(),
})

export const Route = createFileRoute('/search')({
  validateSearch: searchSchema,
  component: SearchPage,
})
```

## Navigation
- Use `<Link>` for internal navigation — never `<a href>`
- Always pass typed `params` and `search` — the compiler will catch mistakes
```tsx
<Link to="/posts/$postId" params={{ postId: '123' }}>View Post</Link>
```

## Loaders + TanStack Query Integration
```tsx
export const Route = createFileRoute('/posts')({
  loader: ({ context: { queryClient } }) =>
    queryClient.ensureQueryData(postsQueryOptions()),
  component: PostsPage,
})
```

## Router Context for Dependency Injection
```tsx
// __root.tsx
interface RouterContext { queryClient: QueryClient; auth: AuthState }
export const Route = createRootRouteWithContext<RouterContext>()({ component: RootLayout })

// main.tsx
const router = createRouter({ routeTree, context: { queryClient, auth } })
```

## Auth Guards
```tsx
export const Route = createFileRoute('/_auth/dashboard')({
  beforeLoad: ({ context }) => {
    if (!context.auth.isAuthenticated) throw redirect({ to: '/login' })
  },
  component: Dashboard,
})
```

## Performance
- Set `defaultPreload: 'intent'` on router for automatic prefetching on hover/focus
- Use `React.lazy` for route component code splitting
- Install `@tanstack/router-devtools` and render `<TanStackRouterDevtools />` in development