Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/Protocol/RequestParamsMetadata.cs

@@ -0,0 +1,22 @@
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Provides metadata related to the request that provides additional protocol-level information.
+/// </summary>
+/// <remarks>
+/// This class contains properties that are used by the Model Context Protocol
+/// for features like progress tracking and other protocol-specific capabilities.
+/// </remarks>
+public class RequestParamsMetadata
+{
+    /// <summary>
+    /// Gets or sets an opaque token that will be attached to any subsequent progress notifications.
+    /// </summary>
+    /// <remarks>
+    /// The receiver is not obligated to provide these notifications.
+    /// </remarks>
+    [JsonPropertyName("progressToken")]
+    public ProgressToken? ProgressToken { get; set; } = default!;
+}