ensure method
Download and merge a custom layer into the active style.
Implementation
Future<void> ensure(String layerId) async {
if (_ensured.contains(layerId)) return;
final item = _findItem(layerId);
if (item == null) throw Exception('Layer "$layerId" not found in catalog.');
_ensured.add(layerId);
// By default, newly ensured items are hidden to match Web SDK behavior
if (!_layerState.containsKey(layerId)) {
_layerState[layerId] = {'visible': false, 'opacity': 1.0};
}
await _rebuildAndApplyStyle();
}