fix(query-core): handle combine throwing in QueriesObserver#notify

When useSuspenseQueries is used with combine and a query transitions
to pending/error state (e.g. after resetQueries), the combine function
throws because data is undefined despite types narrowing it as defined.

The #notify method calls combine as an optimization to check if the
combined result changed. If combine throws during this check, we now
catch the error and still notify listeners so the framework can
re-suspend or show an error boundary.

Fixes #10129

Author: veeceey

packages/query-core/src/__tests__/queriesObserver.test.tsx

@@ -546,4 +546,43 @@ describe('queriesObserver', () => {
 
     trackPropSpy.mockRestore()
   })
+
+  test('should still notify listeners when combine throws after query reset', async () => {
+    const key1 = queryKey()
+    const queryFn1 = vi.fn().mockReturnValue({ name: 'test' })
+
+    const combine = vi.fn(
+      (results: Array<QueryObserverResult>) => {
+        // This simulates a combine function that assumes data is always defined
+        // (like useSuspenseQueries types suggest)
+        return results.map((r) => (r.data as { name: string }).name)
+      },
+    )
+
+    const observer = new QueriesObserver<Array<string>>(
+      queryClient,
+      [{ queryKey: key1, queryFn: queryFn1 }],
+      { combine },
+    )
+
+    const results: Array<Array<QueryObserverResult>> = []
+    const unsubscribe = observer.subscribe((result) => {
+      results.push(result)
+    })
+
+    // Wait for queries to resolve
+    await vi.advanceTimersByTimeAsync(0)
+
+    // Reset the query - this transitions it to pending state
+    // which should cause combine to throw since data is undefined
+    queryClient.resetQueries({ queryKey: key1 })
+
+    // The listener should still have been notified despite combine throwing
+    const lastResult = results[results.length - 1]
+    expect(lastResult).toBeDefined()
+    expect(lastResult![0]!.status).toBe('pending')
+    expect(lastResult![0]!.data).toBeUndefined()
+
+    unsubscribe()
+  })
 })

packages/query-core/src/queriesObserver.ts

@@ -296,9 +296,23 @@ export class QueriesObserver<
     if (this.hasListeners()) {
       const previousResult = this.#combinedResult
       const newTracked = this.#trackResult(this.#result, this.#observerMatches)
-      const newResult = this.#combineResult(newTracked, this.#options?.combine)
 
-      if (previousResult !== newResult) {
+      let shouldNotify: boolean
+      try {
+        const newResult = this.#combineResult(
+          newTracked,
+          this.#options?.combine,
+        )
+        shouldNotify = previousResult !== newResult
+      } catch {
+        // If combine throws (e.g. when used with useSuspenseQueries and
+        // a query transitions to pending/error state after a reset), we
+        // still need to notify so the framework can re-suspend or show
+        // an error boundary.
+        shouldNotify = true
+      }
+
+      if (shouldNotify) {
         notifyManager.batch(() => {
           this.listeners.forEach((listener) => {
             listener(this.#result)