HydrationBoundary takes unknown as the type as `unknown` instead of `DehydratedState`

[paperclover]

Describe the bug

query/packages/react-query/src/HydrationBoundary.tsx

Line 14 in 5dd11a3

state?: unknown

For a library with so much type safety, this is a bit surprising to see.

A refactor to a utility function code using TanStack React Query accidentally passed { state: DehydratedState, ... } instead of the actual dehydrated state, which silently broke some instances of data prefetching on a production Next.js application.

Your minimal, reproducible example

N/A

Steps to reproduce

import { HydrationBoundary } from "@tanstack/react-query";

const mistaken = { oh_no: true };
const element = <HydrationBoundary state={mistaken}>hello</HydrationBoundary>;

result: no error!

---

the real world situation that ran into this was we had a helper function serverSidePrefetchQueries which helps us avoid some of Next.js pitfalls regarding server components. the usage looked like this:

const state = await serverSidePrefetchQueries([
    queryThingA,
    queryThingB,
});

return <HydrationBoundary state={state}>{client}</HydrationBoundary>

but then the return signature of our helper changed, and these pre-fetches silently stopped working.

Expected behavior

should not pass type checking

How often does this bug happen?

None

Screenshots or Videos

No response

Platform

• OS: macOS 15
• Browser: N/A

Tanstack Query adapter

react-query

TanStack Query version

v4, but issue on v5 as well

TypeScript version

N/A

Additional context

No response