After SERVER-124190, the memory tracker is now a shared pointer. However, we still std::move() it off the opCtx on detach. This could be removed, but there is some behavior that relies on removing the memory tracker off the opCtx in exchange. See if we can change the behavior to allow the opCtx to also keep a copy to simplify understanding. See https://github.com/10gen/mongo/pull/59356#discussion_r3672423770 for more context.