*
         * - in `run`, which can't run until this Runnable is submitted to an executor, which
         *   doesn't happen until below. (And this Executor -- yes, the object is both a Runnable
         *   and an Executor -- is used for only a single `execute` call.)
         */
        ThreadConfinedTaskQueue submittingTaskQueue = requireNonNull(sequencer).latestTaskQueue;