[Bug in dartgen] list fields in toJson miss .toList(), causing jsonEncode failure

[fondoger]

What happened

goctl api dartgen generates Dart toJson() methods for list fields using map(...) without converting the mapped iterable back to a List.

The generated object works for direct map inspection, but fails when passed to jsonEncode(obj.toJson()), because dart:convert cannot encode MappedListIterable.

Generated code

Example generated Dart code:

class GetTopUpProductsResponse {
  final List<TopUpProductItem?> items;

  Map<String, dynamic> toJson() {
    return {
      'items': items.map((i) => i?.toJson()),
    };
  }
}

Error log

Unhandled exception:
Converting object to an encodable object failed: Instance of 'MappedListIterable<TopUpProductItem, Map<String, dynamic>?>'

Expected generated code

The list field should be materialized with .toList():

Map<String, dynamic> toJson() {
  return {
    'items': items.map((i) => i?.toJson()).toList(),
  };
}

Minimal API shape that triggers it

GetTopUpProductsResponse {
    Items []*TopUpProductItem `json:"items"`
}
TopUpProductItem {
    ProductId string `json:"productId"`
}

Suspected source

The issue appears to come from tools/goctl/api/dartgen/gendata.go, where list field serialization is generated without appending .toList().