Stale `select` error from a previous query leaks into the next query's pending result

[hamed-bavar]

Describe the bug

When a select function throws, the error is stored on the observer (#selectError) and surfaced on every result. It is only ever cleared inside the select block itself — which is skipped entirely while data is undefined (queryObserver.ts, createResult). So after switching the observer to a different queryKey (or after resetQueries), the new pending query reports status: 'error' carrying the previous query's select error. With throwOnError or suspense, the stale error is thrown into the error boundary while the new query is still fetching.

Minimal reproducible example

const observer = new QueryObserver(queryClient, {
 queryKey: ['user', 'a'],
 queryFn: fetchUser,
 select: (d) => d.profile.name, // throws for user "a"
})
observer.subscribe(() => {})
// select throws -> status 'error' (correct)

observer.setOptions({
 queryKey: ['user', 'b'], // different, healthy query
 queryFn: fetchUser,
 select: (d) => d.profile.name,
})
observer.getCurrentResult().status // 'error' with user "a"'s error — expected 'pending'

Equivalent in React: useQuery({ queryKey: ['user', id], ... }) where select throws for id "a", then setting id to "b".

Second repro without a key change: after the select error, call queryClient.resetQueries({ queryKey }) — the reset pending state still carries the old select error.

Expected behavior

While the new (or reset) query is fetching and has no data, the result should be { status: 'pending', error: null }. A select error belongs to the data it was computed from; once that data is gone, it should not leak into the next result.

Platform

• @tanstack/query-core (all adapters affected), reproduced on main

Additional context

The cause is that createResult only clears #selectError on a successful select run inside the options.select && data !== undefined block; the if (this.#selectError) check below it then fires unconditionally. Related but distinct from #11011 (which fixes isPlaceholderData when select throws on placeholder data).

I have a fix with regression tests ready and will open a PR.