This caller owns the reservation and may execute.
Opaque lease required to finalize or release the reservation.
OptionaltookOver?: booleanWhether this reservation replaced a stale pending holder.
Completed result associated with the key.
A completed result exists and must be replayed without execution.
Another isolate owns a non-stale reservation.
Outcome of an atomic reservation: execute a newly reserved key, replay a completed record, or report that another isolate still owns the key.