Hole ring winds the wrong way and the lake gets filled

• The lake area is filled with the same translucent blue and hides the satellite basemap
• The shoelace signed area is `1.2e-3` for the outer ring and `3.4e-5` for the inner ring, so both are positive
• QGIS geometry validity checks pass and the area computation is correct, so the geometry itself is fine

1. Compute the signed area of each ring with the shoelace formula; outer and inner must have opposite signs
2. Run a QGIS validity check for `Ring Self-intersection` or `Hole lies outside shell`
3. Temporarily switch the fill rule to `evenodd` and see whether the hole appears
4. Compare the winding against RFC 7946: outer counter-clockwise, inner clockwise
5. Check whether the data provider rewound rings during export

Rewind rings before rendering, outer counter-clockwise (positive area) and inner clockwise (negative), by reversing any ring whose sign does not match; as a fallback set `fill-rule: evenodd` on the SVG path via `layer._path.setAttribute('fill-rule', 'evenodd')`.

function signedArea(ring) {
  let s = 0;
  for (let i = 0, n = ring.length; i < n - 1; i++) {
    s += ring[i][0] * ring[i + 1][1] - ring[i + 1][0] * ring[i][1];
  }
  return s / 2;
}

signedArea(poly[0]);   // 外环  1.2e-3  正
signedArea(poly[1]);   // 内环  3.4e-5  正  -> 同号，洞失效

function rewindPolygon(rings) {
  const out = rings.map((ring, i) => {
    const positive = signedArea(ring) > 0;
    const wantPositive = i === 0;        // 外环为正，内环为负
    return positive === wantPositive ? ring : ring.slice().reverse();
  });
  return out;
}

fc.features.forEach(f => {
  if (f.geometry.type !== 'Polygon') return;
  f.geometry.coordinates = rewindPolygon(f.geometry.coordinates);
});

• Assuming QGIS-valid geometry renders correctly, since validity is topological and does not guarantee winding
• Reversing only the outer ring, which makes both rings agree in direction and fills the hole again