Got at least one data fetching method working; turns out, we can't use a patched LogicStack to get the data

Vendor/EmbedIO-3.5.2/Net/Internal/HeaderUtility.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Linq;
+
+namespace EmbedIO.Net.Internal
+{
+    internal static class HeaderUtility
+    {
+        public static string? GetCharset(string? contentType)
+            => contentType?
+                .Split(';')
+                .Select(p => p.Trim())
+                .Where(part => part.StartsWith("charset", StringComparison.OrdinalIgnoreCase))
+                .Select(GetAttributeValue)
+                .FirstOrDefault();
+
+        public static string? GetAttributeValue(string nameAndValue)
+        {
+            var idx = nameAndValue.IndexOf('=');
+
+            return idx < 0 || idx == nameAndValue.Length - 1 ? null : nameAndValue.Substring(idx + 1).Trim().Unquote();
+        }
+    }
+}