cmd_id() :: RaftedValue.command_identifier
t() :: {:queue.queue(cmd_id), %{optional(cmd_id) => any}}
fetch(t, cmd_id) :: {:ok, any} | :error
new() :: t
put(t, cmd_id, any, pos_integer) :: t
validate(any) :: Croma.Result.t(<a href="#t:t/0">t</a>)