[Bug] Ordering by children can be nondeterministic

Bug report

With a schema like

type Parent @entity {
  id: Bytes!
 child: Child!
}

type Child @entity {
  id: Bytes!
}

the result for a query like

query { parents(orderBy: child__id) } { id } }

is nondeterministic if multiple parents point to the same child. To make this entirely clear, assume there is only one instance of Child. The SQL query that gets generated is roughly

select * 
  from parent p 
    left join child c on (c.id = p.child) 
where ...
order by c.id

But when multiple rows in p have the same p.child, that ordering is ill-defined. We'd need to change that to order by c.id, p.id to make that deterministic.

No file or test is named in the issue. Reproduce the GraphQL query with multiple parents pointing to one child, inspect the generated SQL ordering, and trace the query-generation entry point responsible for child__id ordering. Done means equivalent results are deterministic when joined child values tie, while preserving the requested ordering.