Adding Cancellation back to McpSession for all requests. Accidental removal from bad merge.

Author: Tyler-R-Kendrick

src/ModelContextProtocol/Shared/McpSession.cs

@@ -310,6 +310,19 @@ await _transport.SendMessageAsync(new JsonRpcResponse
         }, cancellationToken).ConfigureAwait(false);
     }
 
+    private void RegisterCancellation(CancellationToken cancellationToken, RequestId requestId)
+    {
+        cancellationToken.Register(async () => await SendMessageAsync(new JsonRpcNotification
+        {
+            Method = NotificationMethods.CancelledNotification,
+            Params = JsonSerializer.SerializeToNode(new CancelledNotification
+            {
+                RequestId = requestId,
+                Reason = "Request cancelled"
+            }, McpJsonUtilities.JsonContext.Default.CancelledNotification)
+        }, cancellationToken));
+    }
+
     /// <summary>
     /// Sends a JSON-RPC request to the server.
     /// It is strongly recommended use the capability-specific methods instead of this one.
@@ -320,6 +333,7 @@ await _transport.SendMessageAsync(new JsonRpcResponse
     /// <returns>A task containing the server's response.</returns>
     public async Task<JsonRpcResponse> SendRequestAsync(JsonRpcRequest request, CancellationToken cancellationToken)
     {
+        RegisterCancellation(cancellationToken, request.Id);
         if (!_transport.IsConnected)
         {
             _logger.EndpointNotConnected(EndpointName);