Rendering feature labels in mapnik

I am trying to render a mapnik stylesheet but nothing I try will render the labels. Here is my stylesheet:

<Map srs="+init=epsg:4326">
  <Style name="Polygon">
    <Rule>
      <LineSymbolizer stroke="black" stroke-width="2" />
      <TextSymbolizer face-name="DejaVu Sans" placement="interior" allow-overlap="true">[name]</TextSymbolizer>
    </Rule>
  </Style>
  <Layer name="polygon" srs="+init=epsg:4326">
    <StyleName>Polygon</StyleName>
    <Datasource>
      <Parameter name="type">geojson</Parameter>
      <Parameter name="inline"><![CDATA[
{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "coordinates": [[
          [18.6609649658203, -32.59028569040753],
          [18.6536693572998, -32.59762547484460],
          [18.6737108230590, -32.59892704873228],
          [18.6609649658203, -32.59028569040753]
        ]],
        "type": "Polygon"
      },
      "properties": {
        "name": "polygon"
      }
    }
  ]
}
      ]]>
      </Parameter>
    </Datasource>
  </Layer>
</Map>

The map itself renders fine, but I can't get a label to appear. I am using node-mapnik which I've wrapped in a service inside a docker image, my code is here. I am loading the default fonts, and I have tried several variations on the syntax for <TextSymbolizer> but nothing makes any difference, the labels just don't appear.

For anyone else encountering this (because mapnik's docs are incomplete and in cases plain wrong) you need to load system fonts, not default fonts. In the code:

const mapnik = require('mapnik');
mapnik.register_system_fonts();

Mapnik's example code for node shows mapnik.register_default_fonts();, but the folder that the fonts are supposed to be loaded from is empty and I can't see where they are supposed to come from.