Implement MCP task support (SEP-1686) (#1170)

Co-authored-by: Stephen Halter <halter73@gmail.com>

src/ModelContextProtocol.Core/Server/TaskExecutionContext.cs

@@ -0,0 +1,47 @@
+namespace ModelContextProtocol.Server;
+
+/// <summary>
+/// Represents the execution context for a task being executed by the server.
+/// This context flows with async execution and enables automatic task status updates.
+/// </summary>
+internal sealed class TaskExecutionContext
+{
+    /// <summary>
+    /// Gets the AsyncLocal instance used to track the current task execution context.
+    /// </summary>
+    private static readonly AsyncLocal<TaskExecutionContext?> s_current = new();
+
+    /// <summary>
+    /// Gets or sets the current task execution context for the executing async flow.
+    /// </summary>
+    public static TaskExecutionContext? Current
+    {
+        get => s_current.Value;
+        set => s_current.Value = value;
+    }
+
+    /// <summary>
+    /// Gets the task ID of the currently executing task.
+    /// </summary>
+    public required string TaskId { get; init; }
+
+    /// <summary>
+    /// Gets the session ID associated with the task.
+    /// </summary>
+    public string? SessionId { get; init; }
+
+    /// <summary>
+    /// Gets the task store used to persist task state.
+    /// </summary>
+    public required IMcpTaskStore TaskStore { get; init; }
+
+    /// <summary>
+    /// Gets whether task status notifications should be sent.
+    /// </summary>
+    public bool SendNotifications { get; init; }
+
+    /// <summary>
+    /// Gets or sets the function to call when sending a task status notification.
+    /// </summary>
+    public Func<Protocol.McpTask, CancellationToken, Task>? NotifyTaskStatusFunc { get; init; }
+}