private static string DetectConverterFromJsonEntries(IArchiveReader archive)
{
    var votes = new Dictionary<string,int>(StringComparer.OrdinalIgnoreCase);
    foreach (var entry in archive.Entries.Where(e => e.Name.EndsWith(".json", StringComparison.OrdinalIgnoreCase)))
    {
        var head = archive.ReadHeadUtf8(entry, 64 * 1024); // light read
        switch (ClassifyJsonHeader(head))
        {
            case JsonFormatDetector.Format.TopoJson:  votes.Increment("TopoJson"); break;
            case JsonFormatDetector.Format.EsriJson:  votes.Increment("EsriJson"); break;
            case JsonFormatDetector.Format.GeoJsonSeq:votes.Increment("GeoJsonSeq"); break;
            case JsonFormatDetector.Format.GeoJson:   votes.Increment("GeoJson"); break;
        }
    }
    if (votes.Count == 0) return null;

    // pick majority; if tie, return null to emit a friendly ambiguity message
    var max = votes.Values.Max();
    var winners = votes.Where(kv => kv.Value == max).Select(kv => kv.Key).ToArray();
    return winners.Length == 1 ? winners[0] : null;
}
``