I would like to extend the Stamen Toner map style (https://github.com/stamen/toner-carto/) with a layer to render piers (Way:area,man_made=pier).

I managed to install tilemill on Ubuntu (https://tilemill-project.github.io/tilemill/docs/linux-install/) and also was able to render the resulting XML style with a separate Mapnik install (https://switch2osm.org/serving-tiles/manually-building-a-tile-server-ubuntu-22-04-lts/).

The layer definitions / postgis queries seem to be made in https://github.com/stamen/toner-carto/blob/master/toner.yml

What would be the correct entry to create a piers layer and style it with e.g.

#piers{
  line-width: 0.25;
  polygon-fill: @color_physical_bright;
  line-color: @color_administrative_lowzoom;
}