Adding a base class for request params that exposes the progressToken

This aligns more with the type structure see in the other SDK's (eg: https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/types.py#L41) while also ensuring they are exposing the JSONRPCRequest (https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json#L771-L806) data.

Storing progressToken as an object as it could be an int or string (per https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json#L1268-L1274).

Fixes #67

Author: aaronpowell

src/ModelContextProtocol/Protocol/Types/CallToolRequestParams.cs

@@ -4,7 +4,7 @@
 /// Used by the client to invoke a tool provided by the server.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public class CallToolRequestParams
+public class CallToolRequestParams : RequestParams
 {
     /// <summary>
     /// Tool name.

src/ModelContextProtocol/Protocol/Types/CompleteRequestParams.cs

@@ -4,7 +4,7 @@
 /// A request from the client to the server, to ask for completion options.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public class CompleteRequestParams
+public class CompleteRequestParams : RequestParams
 {
     /// <summary>
     /// The reference's information

src/ModelContextProtocol/Protocol/Types/CreateMessageRequestParams.cs

@@ -9,7 +9,7 @@
 /// clients have full discretion over model selection and should inform users before sampling.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public class CreateMessageRequestParams
+public class CreateMessageRequestParams : RequestParams
 {
     /// <summary>
     /// A request to include context from one or more MCP servers (including the caller), to be attached to the prompt. The client MAY ignore this request.

src/ModelContextProtocol/Protocol/Types/GetPromptRequestParams.cs

@@ -4,7 +4,7 @@
 /// Used by the client to get a prompt provided by the server.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public class GetPromptRequestParams
+public class GetPromptRequestParams : RequestParams
 {
     /// <summary>
     /// he name of the prompt or prompt template.

src/ModelContextProtocol/Protocol/Types/InitializeRequestParams.cs

@@ -6,7 +6,7 @@ namespace ModelContextProtocol.Protocol.Types;
 /// Parameters for an initialization request sent to the server.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public record InitializeRequestParams
+public class InitializeRequestParams : RequestParams
 {
     /// <summary>
     /// The version of the Model Context Protocol that the client wants to use.

src/ModelContextProtocol/Protocol/Types/ReadResourceRequestParams.cs

@@ -4,7 +4,7 @@
 /// Sent from the client to the server, to read a specific resource URI.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public class ReadResourceRequestParams
+public class ReadResourceRequestParams : RequestParams
 {
     /// <summary>
     /// The URI of the resource to read. The URI can use any protocol; it is up to the server how to interpret it.

src/ModelContextProtocol/Protocol/Types/RequestParams.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Base class for all request parameters.
+/// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json#L771-L806">See the schema for details</see>
+/// </summary>
+public abstract class RequestParams
+{
+    /// <summary>
+    /// Metadata related to the tool invocation.
+    /// </summary>
+    [System.Text.Json.Serialization.JsonPropertyName("_meta")]
+    public RequestParamsMetadata? Meta { get; init; }
+}

src/ModelContextProtocol/Protocol/Types/RequestParamsMetadata.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace ModelContextProtocol.Protocol.Types;
+
+/// <summary>
+/// Metadata related to the request.
+/// </summary>
+public class RequestParamsMetadata
+{
+    /// <summary>
+    /// If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
+    /// </summary>
+    [System.Text.Json.Serialization.JsonPropertyName("progressToken")]
+    public object ProgressToken { get; set; } = default!;
+}

src/ModelContextProtocol/Protocol/Types/SetLevelRequestParams.cs

@@ -6,7 +6,7 @@ namespace ModelContextProtocol.Protocol.Types;
 /// A request from the client to the server, to enable or adjust logging.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public class SetLevelRequestParams
+public class SetLevelRequestParams : RequestParams
 {
     /// <summary>
     /// The level of logging that the client wants to receive from the server. 

src/ModelContextProtocol/Protocol/Types/SubscribeRequestParams.cs

@@ -4,7 +4,7 @@
 /// Sent from the client to request updated notifications from the server whenever a particular primitive changes.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/2024-11-05/schema.json">See the schema for details</see>
 /// </summary>
-public class SubscribeRequestParams
+public class SubscribeRequestParams : RequestParams
 {
     /// <summary>
     /// The URI of the resource to subscribe to. The URI can use any protocol; it is up to the server how to interpret it.