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

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

src/ModelContextProtocol.Core/Protocol/ToolExecution.cs

@@ -0,0 +1,85 @@
+using System.Diagnostics.CodeAnalysis;
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Represents execution-related metadata for a tool.
+/// </summary>
+/// <remarks>
+/// This type provides hints about how a tool should be executed, particularly
+/// regarding task augmentation support.
+/// </remarks>
+[Experimental(Experimentals.Tasks_DiagnosticId, UrlFormat = Experimentals.Tasks_Url)]
+public sealed class ToolExecution
+{
+    /// <summary>
+    /// Gets or sets the level of task augmentation support for this tool.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This property declares whether a tool supports task-augmented execution:
+    /// <list type="bullet">
+    /// <item><description><see cref="ToolTaskSupport.Forbidden"/>: Clients must not attempt to invoke 
+    /// the tool as a task. This is the default behavior.</description></item>
+    /// <item><description><see cref="ToolTaskSupport.Optional"/>: Clients may invoke the tool as a task 
+    /// or as a normal request.</description></item>
+    /// <item><description><see cref="ToolTaskSupport.Required"/>: Clients must invoke the tool as a task.
+    /// </description></item>
+    /// </list>
+    /// </para>
+    /// <para>
+    /// This is a fine-grained layer in addition to server capabilities. Even if a server's capabilities
+    /// include tasks.requests.tools.call, this property controls whether each specific tool supports tasks.
+    /// </para>
+    /// </remarks>
+    [JsonPropertyName("taskSupport")]
+    public ToolTaskSupport? TaskSupport { get; set; }
+}
+
+/// <summary>
+/// Represents the level of task augmentation support for a tool.
+/// </summary>
+/// <remarks>
+/// <para>
+/// This enum defines how a tool interacts with the task augmentation system:
+/// <list type="bullet">
+/// <item><description><see cref="Forbidden"/>: Task augmentation is not allowed (default)</description></item>
+/// <item><description><see cref="Optional"/>: Task augmentation is supported but not required</description></item>
+/// <item><description><see cref="Required"/>: Task augmentation is mandatory</description></item>
+/// </list>
+/// </para>
+/// </remarks>
+[Experimental(Experimentals.Tasks_DiagnosticId, UrlFormat = Experimentals.Tasks_Url)]
+[JsonConverter(typeof(JsonStringEnumConverter<ToolTaskSupport>))]
+public enum ToolTaskSupport
+{
+    /// <summary>
+    /// Clients must not attempt to invoke the tool as a task.
+    /// </summary>
+    /// <remarks>
+    /// This is the default behavior. Servers should return a -32601 (Method not found) error
+    /// if a client attempts to invoke the tool as a task when this is set.
+    /// </remarks>
+    [JsonStringEnumMemberName("forbidden")]
+    Forbidden,
+
+    /// <summary>
+    /// Clients may invoke the tool as a task or as a normal request.
+    /// </summary>
+    /// <remarks>
+    /// When this is set, clients can choose whether to use task augmentation based on their needs.
+    /// </remarks>
+    [JsonStringEnumMemberName("optional")]
+    Optional,
+
+    /// <summary>
+    /// Clients must invoke the tool as a task.
+    /// </summary>
+    /// <remarks>
+    /// Servers must return a -32601 (Method not found) error if a client does not attempt
+    /// to invoke the tool as a task when this is set.
+    /// </remarks>
+    [JsonStringEnumMemberName("required")]
+    Required
+}