Angular: whenStable() resolves while a mutation started with mutate() is still running

Describe the bug

ApplicationRef.whenStable() resolves while a mutation started with mutate() is still running, so tests and SSR see the mutation as untouched.

injectMutation registers the Angular pending task from inside the observer subscription callback:

https://github.com/TanStack/query/blob/main/packages/angular-query-experimental/src/inject-mutation.ts#L135-L146

That callback is wrapped in notifyManager.batchCalls, so it runs in a later task than the mutate() call that started the mutation. In the window between the two there is no pending task, the application counts as stable, and whenStable() resolves right away. At that point the result signals have not been updated either, so status() still reads idle.

mutate() is fire and forget, so there is nothing else holding the application busy. mutateAsync() is not affected in the same way because the caller gets a promise back and can await it.

Your minimal, reproducible example

Failing test against main, added to packages/angular-query-experimental/src/__tests__/pending-tasks.test.ts:

it('should let whenStable wait for a mutation that was just triggered', async () => {
  vi.useRealTimers()

  const app = TestBed.inject(ApplicationRef)

  const mutation = TestBed.runInInjectionContext(() =>
    injectMutation(() => ({
      mutationFn: (value: string) => sleep(5).then(() => value),
    })),
  )

  TestBed.tick()
  mutation.mutate('mutated')

  await app.whenStable()

  expect(mutation.status()).toBe('success')
  expect(mutation.data()).toBe('mutated')
})

On current main this fails with expected 'idle' to be 'success'.

Steps to reproduce

1. Set up a zoneless TestBed with provideTanStackQuery.
2. Create a mutation with injectMutation whose mutationFn takes any real time.
3. Call mutation.mutate(...).
4. await ApplicationRef.whenStable().
5. Read mutation.status().

Expected behavior

whenStable() should not resolve until the mutation has settled, the same way it already waits for queries once they have been reported. Right now the only way to make it wait is to insert an arbitrary setTimeout before calling it.

How often does this bug happen?

Every time

Screenshots or Videos

No response

Platform

Reproduced with the repository test suite on Windows 11, Node 24.

Tanstack Query adapter

angular-query

TanStack Query version

5.101.4 (current main)

TypeScript version

5.9.3

Additional context

The same batching gap exists on the query side and is reported in #9981, #9910 and #10046. This issue is only about the mutation path, which those reports do not cover. I have a fix and a regression test ready and will open a PR.

Start with the pending-task registration in packages/angular-query-experimental/src/inject-mutation.ts#L135-L146 and run the regression case in packages/angular-query-experimental/src/tests/pending-tasks.test.ts. Verify that after mutation.mutate(), ApplicationRef.whenStable() waits for the mutation to settle and the status and data assertions pass without an arbitrary timeout.