+ // single representation of all inflight operations reunified
+ // from OpTracker's shards. TrackedOpRef extends the lifetime
+ // to carry the ops outside of the critical section, and thus
+ // allows to call the visitor without any lock being held.
+ // This simplifies the contract on API at the price of plenty
+ // additional moves and atomic ref-counting. This seems OK as
+ // `visit_ops_in_flight()` is definitely not intended for any
+ // hot path.
+ std::vector<TrackedOpRef> ops_in_flight;