ReadonlyattributionReadonlycacheReadonlykindReadonlyplanCache input for explainQuery(), so the query plan reports this read.
A fresh region carries its manifest identity as the plan's validator; a stale
one deliberately carries none, because a region can be reported stale but
never revalidated without the network the caller does not have.
ReadonlyprovenanceReadonlyregionReadonlyresultReadonlyversion
Attribution for the resources that answered the read.