Implement SEP-2663 Tasks Extension (#1579)

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

tests/ModelContextProtocol.Tests/Server/TaskStoreOrphanedTaskTests.cs

@@ -0,0 +1,82 @@
+using Microsoft.Extensions.DependencyInjection;
+using ModelContextProtocol.Client;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+using System.Runtime.InteropServices;
+using System.Text.Json;
+
+#pragma warning disable MCPEXP001
+
+namespace ModelContextProtocol.Tests.Server;
+
+/// <summary>
+/// Verifies that when both <see cref="McpServerOptions.TaskStore"/> and
+/// <see cref="McpServerHandlers.CallToolWithTaskHandler"/> are configured and the handler returns
+/// <see cref="CreateTaskResult"/> (IsTask = true), the store's pre-created task is failed with a
+/// clear error rather than being orphaned in <see cref="McpTaskStatus.Working"/> forever.
+/// </summary>
+public class TaskStoreOrphanedTaskTests : ClientServerTestBase
+{
+    public TaskStoreOrphanedTaskTests(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();
+            options.TaskStore = new InMemoryMcpTaskStore();
+
+            // Returning IsTask = true here while TaskStore is also configured is the
+            // misconfiguration the server must guard against.
+            options.Handlers.CallToolWithTaskHandler = (context, cancellationToken) =>
+                new ValueTask<ResultOrCreatedTask<CallToolResult>>(new CreateTaskResult
+                {
+                    TaskId = "user-task",
+                    Status = McpTaskStatus.Working,
+                    CreatedAt = DateTimeOffset.UtcNow,
+                    LastUpdatedAt = DateTimeOffset.UtcNow,
+                });
+        });
+    }
+
+    [Fact]
+    public async Task TaskStoreAndHandler_BothCreatingTasks_FailsStoreTaskWithClearError()
+    {
+        await using var client = await CreateMcpClientForServer();
+        var ct = TestContext.Current.CancellationToken;
+
+        // The store's task is created synchronously and its taskId returned to the client.
+        var augmented = await client.CallToolRawAsync(
+            new CallToolRequestParams { Name = "anything" }, ct);
+
+        Assert.True(augmented.IsTask);
+        var taskId = augmented.TaskCreated!.TaskId;
+
+        // Poll until the background runner observes the handler's IsTask=true and fails the
+        // store's task. Without the fix this would loop forever in Working.
+        GetTaskResult? taskResult = null;
+        for (int i = 0; i < 40; i++)
+        {
+            await Task.Delay(50, ct);
+            taskResult = await client.GetTaskAsync(taskId, ct);
+            if (taskResult is FailedTaskResult)
+            {
+                break;
+            }
+        }
+
+        var failed = Assert.IsType<FailedTaskResult>(taskResult);
+        Assert.Equal(JsonValueKind.Object, failed.Error.ValueKind);
+        Assert.Equal((int)McpErrorCode.InternalError, failed.Error.GetProperty("code").GetInt32());
+
+        var message = failed.Error.GetProperty("message").GetString();
+        Assert.NotNull(message);
+        Assert.Contains(nameof(McpServerOptions.TaskStore), message);
+        Assert.Contains(nameof(McpServerHandlers.CallToolWithTaskHandler), message);
+    }
+}