Non-derivable per-node payload rides the node that owns it. Tagging all
four deploy nodes with the approval id would render the same card four
times in `dag_view`.
Also fix `set_queue_step`'s doc comment, which claimed the DAG-id lookup
was exact because approval DAGs are single-node. They are not anymore;
what actually holds is that the chain is strictly sequential with the
root parked in Finishing, so at most one node is ever Running.
816006fd48