fix(examples): fix Missing queryFn error in nextjs-app-router example (React Example: Nextjs App Prefetching)

[Globalkmaria]

What this PR does

This PR fixes a hydration error that occurs in the examples/nextjs-app-prefetching example, specifically in the React Example: Nextjs App Prefetching documentation.

Changes made:

• Added await before queryClient.prefetchQuery on the server to ensure data fetching completes before dehydrate(queryClient).

Why

While visiting the TanStack Query documentation example,
I encountered the following error:

⨯ Error: Missing queryFn: ‘[“pokemon”]’
at Array.forEach ()
{ digest: ‘1532731130’ }

This happened because:

• prefetchQuery was not awaited on the server, so dehydrate(queryClient) serialized a query still in "pending" state.
• In TanStack Query, during dehydration, only queryKey and state are serialized.
  The queryFn is never serialized, because JavaScript functions cannot be transferred via JSON.
• Therefore, when the client hydrated and used useSuspenseQuery, the QueryClient had the queryKey but no associated queryFn, causing a Missing queryFn error.

This PR ensures that:

• Prefetching is completed before dehydration.
• The same QueryClient instance is used consistently across server and client.
• Hydration succeeds without missing functions.
• Suspense works properly with server-prefetched queries.

Testing

• Ran examples/nextjs-app-router locally.
• Verified:
  • No hydration errors occur after the fix.
  • Immediate rendering with prehydrated data.
  • Correct fallback loading UI when no prefetch exists.
• No runtime errors or warnings observed.

Notes

• This fix is isolated to the example app; no core TanStack Query code is changed.
• Improves the developer onboarding experience by preventing a common hydration pitfall when using useSuspenseQuery and Next.js App Router together.
• Based on the current React Query v5 behavior where only queryKey and state are serialized during dehydration.

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Thank you for maintaining such a great project! 🚀
Happy to adjust anything based on reviewer feedback.

[Globalkmaria]

Hi team 👋
Encountered this real error when visiting the docs example and fixed it. Happy to adjust anything if needed 🚀