There is already a github team for the entire query team ("@10gen/query"), so after discussing with mihai.andrei@mongodb.com we think that the best solution for now is to give ownership of jointly owned files to this github team. My understanding is that due to a github limitation, there is no way to enforce that changes to these files are approved by both a member of QE and a member of QO. Another potential downside QI team is also included in "@10gen/query", but this seems acceptable for files that are currently fully shared across the entire query processing pipeline.

The main directories that we want to handle with this ticket are db/matcher/ and db/pipeline/, but we should also look for other files that should have shared ownership across all of query.

In the long run, it would be good to split up DocumentSource, MatchExpression, and Expression into separate compile-time and runtime representations, but doing so is non-trivial and should not block the effort to add owners files.