Add initial task extension conformance coverage (#1734)

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 7c99928c-a943-49f4-9a63-8b04a0e4d18b

tests/ModelContextProtocol.Tests/Client/McpClientTaskMethodsTests.cs

@@ -154,9 +154,10 @@ public class McpClientTaskMethodsTests : ClientServerTestBase
         {
             await client.CancelTaskAsync(taskId, ct);
 
-            // If cancel succeeded, verify the task is cancelled
+            // Cancellation is eventually consistent. The task may complete before the cancellation
+            // request wins the race, but the terminal-task cancellation acknowledgement is idempotent.
             var taskResult = await client.GetTaskAsync(taskId, ct);
-            Assert.IsType<CancelledTaskResult>(taskResult);
+            Assert.True(taskResult is CancelledTaskResult or CompletedTaskResult);
         }
         catch (McpProtocolException)
         {

tests/ModelContextProtocol.Tests/Protocol/TaskSerializationTests.cs

@@ -91,6 +91,18 @@ public static class TaskSerializationTests
 
     #endregion
 
+    [Theory]
+    [InlineData(typeof(UpdateTaskResult))]
+    [InlineData(typeof(CancelTaskResult))]
+    public static void TaskAcknowledgement_SerializesExplicitCompleteResultType(Type resultType)
+    {
+        var result = (Result)Activator.CreateInstance(resultType)!;
+
+        var json = JsonSerializer.SerializeToNode(result, resultType, McpTasksJsonContext.Default.Options)!;
+
+        Assert.Equal("complete", (string)json["resultType"]!);
+    }
+
     #region GetTaskResult Subtypes
 
     [Fact]

tests/ModelContextProtocol.Tests/Server/CustomRequestHandlerCollisionTests.cs

@@ -75,5 +75,28 @@ public class CustomRequestHandlerCollisionTests(ITestOutputHelper testOutputHelp
         await using var server = McpServer.Create(transport, options, LoggerFactory);
         Assert.NotNull(server);
     }
+
+    [Fact]
+    public async Task CustomHandler_EmptyRoutingNameParameter_Throws()
+    {
+        await using var transport = new StreamServerTransport(Stream.Null, Stream.Null);
+        var options = new McpServerOptions
+        {
+            RequestHandlers =
+            [
+                new McpServerRequestHandler
+                {
+                    Method = "custom/method",
+                    RoutingNameParameter = " ",
+                    Handler = (request, cancellationToken) => new ValueTask<JsonNode?>((JsonNode?)null),
+                },
+            ],
+        };
+
+        var ex = Assert.Throws<InvalidOperationException>(
+            () => McpServer.Create(transport, options, LoggerFactory));
+
+        Assert.Contains(nameof(McpServerRequestHandler.RoutingNameParameter), ex.Message);
+    }
 #pragma warning restore MCPEXP002
 }