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

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

src/ModelContextProtocol.Core/Protocol/RequestMethods.cs

@@ -121,4 +121,32 @@ public static class RequestMethods
     /// and information, establishing the protocol version and available features for the session.
     /// </remarks>
     public const string Initialize = "initialize";
+
+    /// <summary>
+    /// The name of the request method to retrieve task status.
+    /// </summary>
+    /// <remarks>
+    /// Requestors poll for task completion by sending tasks/get requests. They should respect
+    /// the pollInterval provided in responses when determining polling frequency.
+    /// </remarks>
+    public const string TasksGet = "tasks/get";
+
+    /// <summary>
+    /// The name of the request method to retrieve the result of a completed task.
+    /// </summary>
+    /// <remarks>
+    /// This request blocks until the task reaches a terminal status (completed, failed, or cancelled).
+    /// The result structure matches the original request type (e.g., CallToolResult for tools/call).
+    /// </remarks>
+    public const string TasksResult = "tasks/result";
+
+    /// <summary>
+    /// The name of the request method to retrieve a list of tasks with pagination support.
+    /// </summary>
+    public const string TasksList = "tasks/list";
+
+    /// <summary>
+    /// The name of the request method to explicitly cancel a task.
+    /// </summary>
+    public const string TasksCancel = "tasks/cancel";
 }