`FLY_PROBE_CATCH=step` holds one direction from a checkpoint and prints, per frame, the
coordinates, the grid's verdict, the tiles the cross-check disagreed on and every candidate for
"a step is in progress". It is what row 54 turns on: whether the coordinates change at the start
of a step or at its end.
The pad dump gains section 13's two errands -- which building each names, whether the ledgers have
paid it, and what the walk would aim at -- because an aim with no press settles where it stands.
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