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+---
+description: Guidelines for building TanStack Start applications
+---
+
+# TanStack Start with Shadcn/ui Development Guide
+
+You are an expert TypeScript developer specializing in TanStack Start applications with modern React patterns.
+
+## Tech Stack
+- TypeScript (strict mode)
+- TanStack Start (routing & SSR)
+- Shadcn/ui (UI components)
+- Tailwind CSS (styling)
+- Zod (validation)
+- TanStack Query (client state)
+
+## Code Style Rules
+
+- NEVER use `any` type - always use proper TypeScript types
+- Prefer function components over class components
+- Use `@/` alias for all internal imports
+- Always validate external data with Zod schemas
+- Include error and pending boundaries for all routes
+- Follow accessibility best practices with ARIA attributes
+
+## Component Patterns
+
+Use function components with proper TypeScript interfaces:
+
+```typescript
+interface ButtonProps {
+  children: React.ReactNode;
+  onClick: () => void;
+  variant?: 'primary' | 'secondary';
+}
+
+export default function Button({ children, onClick, variant = 'primary' }: ButtonProps) {
+  return (
+    <button onClick={onClick} className={cn(buttonVariants({ variant }))}>
+      {children}
+    </button>
+  );
+}
+```
+
+## Data Fetching
+
+Use Route Loaders for:
+- Initial page data required for rendering
+- SSR requirements
+- SEO-critical data
+
+Use React Query for:
+- Frequently updating data
+- Optional/secondary data
+- Client mutations with optimistic updates
+
+```typescript
+// Route Loader
+export const Route = createFileRoute('/users')({
+  loader: async () => {
+    const users = await fetchUsers()
+    return { users: userListSchema.parse(users) }
+  },
+  component: UserList,
+})
+
+// React Query
+const { data: stats } = useQuery({
+  queryKey: ['user-stats', userId],
+  queryFn: () => fetchUserStats(userId),
+  refetchInterval: 30000,
+});
+```
+
+## Zod Validation
+
+Always validate external data. Define schemas in `src/lib/schemas.ts`:
+
+```typescript
+export const userSchema = z.object({
+  id: z.string(),
+  name: z.string().min(1).max(100),
+  email: z.string().email().optional(),
+  role: z.enum(['admin', 'user']).default('user'),
+})
+
+export type User = z.infer<typeof userSchema>
+
+// Safe parsing
+const result = userSchema.safeParse(data)
+if (!result.success) {
+  console.error('Validation failed:', result.error.format())
+  return null
+}
+```
+
+## Routes
+
+Structure routes in `src/routes/` with file-based routing. Always include error and pending boundaries:
+
+```typescript
+export const Route = createFileRoute('/users/$id')({
+  loader: async ({ params }) => {
+    const user = await fetchUser(params.id);
+    return { user: userSchema.parse(user) };
+  },
+  component: UserDetail,
+  errorBoundary: ({ error }) => (
+    <div className="text-red-600 p-4">Error: {error.message}</div>
+  ),
+  pendingBoundary: () => (
+    <div className="flex items-center justify-center p-4">
+      <div className="animate-spin rounded-full h-8 w-8 border-b-2 border-primary" />
+    </div>
+  ),
+});
+```
+
+## UI Components
+
+Always prefer Shadcn/ui components over custom ones:
+
+```typescript
+import { Button } from '@/components/ui/button';
+import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
+
+<Card>
+  <CardHeader>
+    <CardTitle>User Details</CardTitle>
+  </CardHeader>
+  <CardContent>
+    <Button onClick={handleSave}>Save</Button>
+  </CardContent>
+</Card>
+```
+
+Use Tailwind for styling with responsive design:
+
+```typescript
+<div className="flex flex-col gap-4 p-6 md:flex-row md:gap-6">
+  <Button className="w-full md:w-auto">Action</Button>
+</div>
+```
+
+## Accessibility
+
+Use semantic HTML first. Only add ARIA when no semantic equivalent exists:
+
+```typescript
+// ✅ Good: Semantic HTML with minimal ARIA
+<button onClick={toggleMenu}>
+  <MenuIcon aria-hidden="true" />
+  <span className="sr-only">Toggle Menu</span>
+</button>
+
+// ✅ Good: ARIA only when needed (for dynamic states)
+<button
+  aria-expanded={isOpen}
+  aria-controls="menu"
+  onClick={toggleMenu}
+>
+  Menu
+</button>
+
+// ✅ Good: Semantic form elements
+<label htmlFor="email">Email Address</label>
+<input id="email" type="email" />
+{errors.email && (
+  <p role="alert">{errors.email}</p>
+)}
+```
+
+## File Organization
+
+```
+src/
+├── components/ui/    # Shadcn/ui components
+├── lib/schemas.ts    # Zod schemas
+├── routes/          # File-based routes
+└── routes/api/      # Server routes (.ts)
+```
+
+## Import Standards
+
+Use `@/` alias for all internal imports:
+
+```typescript
+// ✅ Good
+import { Button } from '@/components/ui/button'
+import { userSchema } from '@/lib/schemas'
+
+// ❌ Bad
+import { Button } from '../components/ui/button'
+```
+
+## Adding Components
+
+Install Shadcn components when needed:
+
+```bash
+npx shadcn@latest add button card input dialog
+```
+
+## Common Patterns
+
+- Always validate external data with Zod
+- Use route loaders for initial data, React Query for updates
+- Include error/pending boundaries on all routes
+- Prefer Shadcn components over custom UI
+- Use `@/` imports consistently
+- Follow accessibility best practices
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