Fix the event subscription in dotnet

dotnet/src/Client.cs

@@ -759,12 +759,13 @@ public async ValueTask DisposeAsync()
     private class RpcHandler(CopilotClient client)
     {
         [JsonRpcMethod("session.event")]
-        public void OnSessionEvent(SessionEventNotification notification)
+        public void OnSessionEvent(string sessionId,
+            JsonElement? @event)
         {
-            var session = client.GetSession(notification.SessionId);
-            if (session != null && notification.Event != null)
+            var session = client.GetSession(sessionId);
+            if (session != null && @event != null)
             {
-                var evt = SessionEvent.FromJson(notification.Event.ToString());
+                var evt = SessionEvent.FromJson(@event.Value.GetRawText());
                 session.DispatchEvent(evt);
             }
         }
@@ -957,10 +958,6 @@ private record DeleteSessionResponse(
     private record ListSessionsResponse(
         List<SessionMetadata> Sessions);
 
-    private record SessionEventNotification(
-        string SessionId,
-        JToken? Event);
-
     private record ToolCallResponse(
         ToolResultObject? Result);
 

dotnet/test/SessionTests.cs

@@ -285,4 +285,36 @@ public async Task Should_Pass_Streaming_Option_To_Session_Creation()
         Assert.NotNull(assistantMessage);
         Assert.Contains("2", assistantMessage!.Data.Content);
     }
+
+    [Fact]
+    public async Task Should_SessionEvt_Subscribed()
+    {
+        var session = await Client.CreateSessionAsync();
+        var receivedEvents = new List<SessionEvent>();
+        var idleReceived = new TaskCompletionSource<bool>();
+
+        session.On(evt =>
+        {
+            receivedEvents.Add(evt);
+            if (evt is SessionIdleEvent)
+            {
+                idleReceived.TrySetResult(true);
+            }
+        });
+
+        // Send a message to trigger events
+        await session.SendAsync(new MessageOptions { Prompt = "Hello!" });
+
+        // Wait for session to become idle (indicating message processing is complete)
+        var completed = await Task.WhenAny(idleReceived.Task, Task.Delay(TimeSpan.FromSeconds(60)));
+        Assert.Equal(idleReceived.Task, completed);
+
+        // Should have received multiple events (user message, assistant message, idle, etc.)
+        Assert.NotEmpty(receivedEvents);
+        Assert.Contains(receivedEvents, evt => evt is UserMessageEvent);
+        Assert.Contains(receivedEvents, evt => evt is AssistantMessageEvent);
+        Assert.Contains(receivedEvents, evt => evt is SessionIdleEvent);
+
+        await session.DisposeAsync();
+    }
 }