C#: a remembered refusal keeps its code and field, never the write's strings, and replays in fixed text; a write on an unreliable channel of a receipt session is refused message_invalid (channel)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/GameCult.Networking/Server.cs

@@ -415,6 +415,7 @@ namespace GameCult.Networking
                     {
                         var cultNetMessage = LiteNetLibTransportConnection.DecodeSchema(frame);
                         Logger.LogDebug($"Received CultNet schema message {cultNetMessage.SchemaVersion}");
+                        if (transport.RefuseUnreliableWrite(cultNetMessage, method)) return;
                         await HandleCultNetSchemaMessageAsync(peer, user, cultNetMessage).ConfigureAwait(false);
                         return;
                     }