Default draft protocol support: sessionless + handshake-less (SEP-2575 + SEP-2567) (#1610)

tests/ModelContextProtocol.Tests/Protocol/CancellationTests.cs

@@ -84,6 +84,9 @@ public class CancellationTests : ClientServerTestBase
 
         var clientOptions = new McpClientOptions
         {
+            // Pin to a legacy protocol version so the client performs the initialize handshake
+            // (the spec rule under test is "the initialize request MUST NOT be cancelled by clients").
+            ProtocolVersion = "2025-11-25",
             InitializationTimeout = TimeSpan.FromMilliseconds(500),
         };