BUILD-LOCALIZATION-SURVIVES-THE-PROVIDER-SWAP asked for a check; the
behaviour landed in 319064a1 (library/maps/localize-labels.js) without
one. This reads the labels the map actually DRAWS, at ?lang=en and
?lang=ru on the same view, under both providers:
Mapbox the Standard basemap's 'place-labels' featureset (a plain
queryRenderedFeatures cannot see the imported basemap):
Germany→Германия, Ukraine→Украина, Egypt→Египет… must flip.
MapLibre each country symbol's evaluated text-field: under ru it must
be the feature's name:ru, under en not. English there
restores OSM's own label, so no English word is expected.
It serves this checkout on an OS-assigned port. --dir points it at
another tree for the negative control.
Negative-tested: doxa-simple-map built from 319064a1's parent (no
localize-labels) and served with --dir FAILS on both engines (Mapbox:
68 country labels, none flip; MapLibre: 0/49 in Russian). This tree
PASSES on both (5 known countries flip on Mapbox; 49/49 on MapLibre,
e.g. United Kingdom → Великобритания). A first version counted the
pre-fix Mapbox run as NOT MEASURED instead of FAIL, since it saw no
English names. "Measured" now means enough country labels were drawn.
