CARTO now answers every keyless basemap request with HTTP 200 and a valid
256x256 PNG that is just a dark square watermarked "API KEY REQUIRED".
Leaflet accepts it as a tile and paints it, so the map silently filled with
the warning — no console error, nothing in the network tab to catch it.
Esri's World Dark Gray Canvas is a genuine dark basemap and needs no key.
Its ArcGIS REST service orders the tile path {z}/{y}/{x}, the reverse of
what Leaflet knows how to substitute, so a getTileUrl override is the whole
fix. react-leaflet always instantiates Leaflet's own TileLayer, so the
custom class is added to the map directly and torn down on unmount rather
than passed as a prop.
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