Changing data with useMutation (the real app behind the video)

npm install
npm run dev        # http://localhost:5173

The profile picker from the TanStack Query video, now with a small form under the card. Type a new city for Alice (Mumbai), press Save: the change goes to the server with useMutation. With invalidateQueries in onSuccess, the card refetches and shows the new city; without it, the save works but the card keeps showing the old one until something else refetches it. Open DevTools › Network (Fetch/XHR) to watch the PATCH and the GET after it, and the TanStack Query DevTools (the floating button, bottom right) to see the query go to "fetching" and the mutation succeed.

• vite.config.js serves a tiny API from api/users.json: GET /api/users/:id (Alice is delayed 2 s on purpose, everyone else 0.4 s) and PATCH /api/users/:id (0.6 s), which merges the JSON body into that user and answers with the updated user. The changes live in memory: restarting the dev server puts everyone back (the file is never written).
• src/main.jsx creates one QueryClient and wraps the app in QueryClientProvider (plus ReactQueryDevtools).
• src/versions/ holds each step of the story (see its README). src/Profile.jsx is whichever version was copied in last (the finished app: useMutation + invalidateQueries).

Sources: Mutations · Invalidations from mutations · Query invalidation