When a user references $meta: "searchRootDocumentId" but the $search stage is missing the returnScope field (or returnStoredSource: true), the query fails with a generic, unhelpful error:

query requires $search root document id metadata, but it is not available

This does not tell the user what they actually need to do to fix it.

We should detect the case where $meta: "searchRootDocumentId" is requested while returnStoredSource is set but returnScope is missing, and surface a targeted message. We require both conditions here.