designer/src/
  api/          # API service modules (axios-based)
  assets/       # Static assets and icons
  components/   # Feature-organized React components
    ui/         # Radix-based primitive components
  contexts/     # React Context providers
  hooks/        # Custom hooks (TanStack Query wrappers)
  lib/          # Utilities (cn, etc.)
  types/        # TypeScript type definitions
  utils/        # Helper functions
  test/         # Test utilities, factories, mocks

// Centralized client with interceptors
export const apiClient = axios.create({
  baseURL: API_BASE_URL,
  headers: { 'Content-Type': 'application/json' },
  timeout: 60000,
})

// Error handling interceptor
apiClient.interceptors.response.use(
  response => response,
  (error: AxiosError) => {
    if (error.response?.status === 422) {
      throw new ValidationError('Validation error', error.response.data)
    }
    throw new NetworkError('Request failed', error)
  }
)

const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 60_000,
      gcTime: 5 * 60_000,
      retry: 2,
      retryDelay: attemptIndex => Math.min(1000 * 2 ** attemptIndex, 30_000),
      refetchOnWindowFocus: false,
    },
    mutations: { retry: 1 },
  },
})

// lib/utils.ts - Always use cn() for Tailwind classes
import { clsx, type ClassValue } from 'clsx'
import { twMerge } from 'tailwind-merge'

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs))
}

const ThemeContext = createContext<ThemeContextType | undefined>(undefined)

export function useTheme() {
  const context = useContext(ThemeContext)
  if (!context) throw new Error('useTheme must be used within ThemeProvider')
  return context
}

// Apply via Tailwind dark mode class strategy
useEffect(() => {
  document.documentElement.classList.toggle('dark', theme === 'dark')
}, [theme])

// Use MSW for API mocking
import { server } from '@/test/mocks/server'
import { renderWithProviders } from '@/test/utils'

beforeAll(() => server.listen())
afterEach(() => server.resetHandlers())
afterAll(() => server.close())

test('renders with query data', async () => {
  renderWithProviders(<MyComponent />)
  await screen.findByText('Expected text')
})