
Filing this issue to track a question/comment that was raised by @ywangd  here https://github.com/elastic/elasticsearch/pull/98309#discussion_r1294115440

One question I do have is why we chose to [execute the LookupRequest with the enrich origin](https://github.com/elastic/elasticsearch/blob/2e4440ff1c0decf79f8a40688566411f7d518aa7/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/enrich/EnrichLookupService.java#L141C2-L141C2). It means the following query works when the user has access to only the playlist index without access to either the songs enrich policy or its associated index.

```
FROM playlist | ENRICH songs ON song_id
```

It feels a bit weird to me that we have no control on who can use what enrich process. That said, we don't have a good story around enrich and ingest pipeline either, i.e. we have no control over who can use what pipeline where a pipeline can contain an enrich processor. There have been quite a few complaints from users and we have an https://github.com/elastic/elasticsearch/issues/57586 for it. I wonder whether we should not repeat the problem here with ES|QL. On the surface, it might be easier to tackle compared to ingest pipelines since ES|QL is read-only and has no "bulk" operations. What do you think?
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizer.java
return pl;
        }
        /**
         * Prunes attributes from the list not found in the given set.
         * Returns null if no changed occurred.
         */
        private static <N extends NamedExpression> List<N> removeUnused(List<N> named, AttributeSet used) {
            var clone = new ArrayList<>(named);
            var it = clone.listIterator(clone.size());
            
            while (it.hasPrevious()) {
                N prev = it.previous();
                if (used.contains(prev.toAttribute()) == false) {
                    it.remove();
                } else {
                    used = used.combine(prev.references());
                }
            }
            return clone.size() != named.size() ? clone : null;
        }
        private static List<Expression> expressions(LogicalPlan plan) {
            List<Expression> exp = new ArrayList<>();
            plan.forEachExpression(exp::add);
            return exp;
        }
        private static AttributeSet references(LogicalPlan plan) {
            return Expressions.references(expressions(plan));
        }
    }
    static class PruneOrderByBeforeStats extends OptimizerRules.OptimizerRule<Aggregate> {