TODO: 
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  - A job submission returns a job id, which can be used to
    check for the job's state as long as the job is running.
    Once the job is finished though, the SAGA adaptor may
    not be able to infer the job state (Done or Failed) from
    that job id.

    One could create a watcher process which keeps track of
    running jobs, and stores their final state in an advert.
    That watcher could safely quit if no further jobs are to
    be watched.