Revalidated promise should also resolve the mutation itself

When i `await mutation().revalidated` it should also await and therefore surface errors from the mutation itself

Start by tracing the implementation of mutation().revalidated and the existing promise or mutation tests. Verify the current await behavior, then ensure awaiting revalidated also surfaces errors from the mutation itself. Done means the behavior is covered by a regression test for both resolution and mutation failure.

Written by the indexing model from the issue text.