One thing I found before dispatching, and filed as Q0579. The halt told you C6
  was all that was left in the unit. That was true of the step's criteria and
  false of the unit's acceptance, which reads "exits 0 AND witnessed red" — two
  conjuncts. The witness half holds; the exits-0 half does not, because hello's
  G7 currently reads DIFFER 554/51340. I re-derived that from the gate map
  rather than trusting the prior step's report. So satisfying C6 does not by
  itself finish this unit, and I've filed that so attempt 1's success can't
  quietly be read as the unit's.