
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
CombineProjections() {
            super(TransformDirection.UP);
        }
        @Override
        protected LogicalPlan rule(UnaryPlan plan) {
            LogicalPlan child = plan.child();
            if (plan instanceof Project project) {
                if (child instanceof Project p) {
                    
                    return p.withProjections(combineProjections(project.projections(), p.projections()));
                } else if (child instanceof Aggregate a) {
                    return new Aggregate(a.source(), a.child(), a.groupings(), combineProjections(project.projections(), a.aggregates()));
                }
            }
            
            if (plan instanceof Aggregate a) {
                if (child instanceof Project p) {
                    return new Aggregate(a.source(), p.child(), a.groupings(), combineProjections(a.aggregates(), p.projections()));
                }
            }
            return plan;
        }