Caught on the sibling mort PR (gadfly/sonnet) and the same mistake was
here: map iteration is randomised, so the matrix printed its cells in a
different order every run and two failing runs could not be diffed. The
"which placements are bare" lookup was a second map keyed by name, which
also let a placement and its expectation drift apart by a typo.
Both are now one slice of {name, bare, build}, so the expectation sits
on the row it belongs to and the order is fixed.