OptionalmaxOptionalresolveDefault true: reaching max resolves and wakes in the same
statement as the completing add. false makes max a cap only;
further adds answer full and the wait ends by timeout or resolve.
OptionaluniqueDefault true: a repeated item key answers duplicate-item. false
replaces the entry in place; the count is unchanged.
Count trigger. Absent means unbounded: only
timeoutor a manual resolve ends the wait.