Демка с чатом работает

Example.Events.Shared/IChat.cs

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+using System;
+using mROA.Implementation;
+using mROA.Implementation.Attributes;
+
+namespace Example.Events.Shared
+{
+    [SharedObjectInterface]
+    public partial interface IChat : IShared
+    {
+        void PostSymbol(string symbol, RequestContext context = default);
+        event Action<string, RequestContext> OnCharPosted;
+    }
+}