Implement SEP-2663 Tasks Extension (#1579)

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

src/ModelContextProtocol.Core/Server/McpTaskInfo.cs

@@ -0,0 +1,28 @@
+using ModelContextProtocol.Protocol;
+using System.Diagnostics.CodeAnalysis;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Server;
+
+/// <summary>
+/// Represents the state of a task in an <see cref="IMcpTaskStore"/>.
+/// </summary>
+/// <remarks>
+/// <para>
+/// This is the store's representation of a task, decoupled from the MCP protocol wire types.
+/// The server infrastructure maps <see cref="McpTaskInfo"/> to the appropriate protocol response
+/// types (<see cref="CreateTaskResult"/>, <see cref="GetTaskResult"/>) when communicating with clients.
+/// </para>
+/// </remarks>
+[Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
+public sealed record McpTaskInfo(
+    string TaskId,
+    McpTaskStatus Status,
+    DateTimeOffset CreatedAt,
+    DateTimeOffset LastUpdatedAt,
+    long? TtlMs = null,
+    long? PollIntervalMs = null,
+    string? StatusMessage = null,
+    JsonElement? Result = null,
+    JsonElement? Error = null,
+    IReadOnlyDictionary<string, InputRequest>? InputRequests = null);