During the classic multiplanner trial period, each candidate plan stores the results it produces in BaseCandidatePlan::results. These buffered results are added by the MultiPlanStage and is not measured or tracked anywhere:

• It is not added to the operation's memory tracker, so it does not show up in peakTrackedMemBytes (slow query log, profiler, $currentOp, query stats).
• There are no serverStatus metric reports it, so it is not visible in FTDC. The only memory-related multiplanner metric is query.multiPlanner.allPlansHitMemoryLimit but this only counts failures and not the actual memory usage.

Open question: How much memory is reported by the blocking stages of the plans being multiplanned? How do we avoid double counting that here?