grab_job:  {
   can_do: [@can_do],
}
  -> {
     jobid,
     job,
     arg,
     # failure_count?
  }
  (or)
  -> Nothing


insert_job: {
  job: "foo",
  arg: "lskdjflksdjflskdf",
  uniqkey: "blah",
  run_after: $unix_time,
  coalesce: "to_foo",
}
  -> jobid


# atomic insert multiple jobs:
insert_jobs:
   [ {...}, {...}, ]

   -> @jobids

mark_completed: {
   jobid: 5,
   replace_with: [@jobs],    #optional
}
   -> { handles => [@handles] }

mark_failed: {
   jobid: 5,
   message: "error message",
   exit_status: 6,
   retry_in: 80,   # optional.  if not present, no retry.
}

get_failure_log: {
   jobid: 6
}
  -> [ {time:2342342,exitstatus ... }, {....}, {...} ]

get_status: {
   jobid: 6,
}
  -> {
       exitstatus: 0,
     }