Implement SEP-2663 Tasks Extension (#1579)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/ModelContextProtocol.Tests/Server/TaskHandlerConfigurationValidationTests.cs

@@ -0,0 +1,59 @@
+using Microsoft.Extensions.DependencyInjection;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+using System.Runtime.InteropServices;
+
+namespace ModelContextProtocol.Tests.Server;
+
+/// <summary>
+/// Verifies the runtime validation that fires when a handler opts into task-augmented execution
+/// (returns a <see cref="CreateTaskResult"/>) without the server having any <c>tasks/get</c>
+/// handler registered.
+/// </summary>
+public class TaskHandlerConfigurationValidationTests : ClientServerTestBase
+{
+    public TaskHandlerConfigurationValidationTests(ITestOutputHelper testOutputHelper) : base(testOutputHelper)
+    {
+#if !NET
+        Assert.SkipWhen(RuntimeInformation.IsOSPlatform(OSPlatform.Windows), "https://github.com/modelcontextprotocol/csharp-sdk/issues/587");
+#endif
+    }
+
+    protected override void ConfigureServices(ServiceCollection services, IMcpServerBuilder mcpServerBuilder)
+    {
+        mcpServerBuilder.Services.Configure<McpServerOptions>(options =>
+        {
+            options.Capabilities ??= new ServerCapabilities();
+
+            // Intentionally configure a task-augmented handler without TaskStore or any of the
+            // task lifecycle handlers (GetTaskHandler/UpdateTaskHandler/CancelTaskHandler).
+            options.Handlers.CallToolWithTaskHandler = (context, cancellationToken) =>
+                new ValueTask<ResultOrCreatedTask<CallToolResult>>(new CreateTaskResult
+                {
+                    TaskId = "orphan-task",
+                    Status = McpTaskStatus.Working,
+                    CreatedAt = DateTimeOffset.UtcNow,
+                    LastUpdatedAt = DateTimeOffset.UtcNow,
+                });
+        });
+    }
+
+    [Fact]
+    public async Task CallTool_ReturningCreateTaskResult_WithoutTasksGetHandler_ThrowsAtRequestTime()
+    {
+        await using var client = await CreateMcpClientForServer();
+
+        // Client surfaces a generic protocol error (the server intentionally redacts the message
+        // on the wire), so use the base McpException type and confirm via server-side logs that
+        // the originating exception was the misconfiguration guard.
+        await Assert.ThrowsAnyAsync<McpException>(async () =>
+            await client.CallToolAsync(
+                new CallToolRequestParams { Name = "anything" },
+                cancellationToken: TestContext.Current.CancellationToken));
+
+        Assert.Contains(MockLoggerProvider.LogMessages, log =>
+            log.Exception is InvalidOperationException ioe &&
+            ioe.Message.Contains("tasks/get", StringComparison.Ordinal) &&
+            ioe.Message.Contains("CreateTaskResult", StringComparison.Ordinal));
+    }
+}