Follow on from SERVER-132033, per claude's suggestion:

How join optimization is reported at planner level. The join executor passes no PlanSelectionStrategy on master; the ticket decides between kCostBasedRanker with a reason such as joinOptimization and a new strategy value, records it in the design doc, passes it from join/executor.cpp, and reinstates the ordering through the shared orderV3PlanCandidates() rule with a unit test of two rejected join plans of known cost. That closes the singlePlan contradiction at the place the design doc owns.