Use existing MCPEXP001 diagnostic and add proper pragma warning restore

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

docs/list-of-diagnostics.md

@@ -23,5 +23,4 @@ If you use experimental APIs, you will get one of the diagnostics shown below. T
 
 | Diagnostic ID | Description |
 | :------------ | :---------- |
-| `MCPEXP001` | MCP experimental APIs including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [MCP Tasks specification](https://modelcontextprotocol.io/specification/draft/basic/utilities/tasks)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |
-| `MCPEXP002` | Subclassing `McpClient` and `McpServer` is experimental and subject to change. |
+| `MCPEXP001` | MCP experimental APIs including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [MCP Tasks specification](https://modelcontextprotocol.io/specification/draft/basic/utilities/tasks)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |

src/Common/Experimentals.cs

@@ -56,19 +56,4 @@ internal static class Experimentals
     /// URL for the experimental MCP Extensions feature.
     /// </summary>
     public const string Extensions_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcpexp001";
-
-    /// <summary>
-    /// Diagnostic ID for experimental subclassing of McpClient and McpServer.
-    /// </summary>
-    public const string Subclassing_DiagnosticId = "MCPEXP002";
-
-    /// <summary>
-    /// Message for experimental subclassing of McpClient and McpServer.
-    /// </summary>
-    public const string Subclassing_Message = "Subclassing McpClient and McpServer is experimental and subject to change.";
-
-    /// <summary>
-    /// URL for experimental subclassing of McpClient and McpServer.
-    /// </summary>
-    public const string Subclassing_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcpexp002";
 }

src/ModelContextProtocol.Core/Client/McpClient.cs

@@ -11,7 +11,7 @@ public abstract partial class McpClient : McpSession
     /// <summary>
     /// Initializes a new instance of the <see cref="McpClient"/> class.
     /// </summary>
-    [Experimental(Experimentals.Subclassing_DiagnosticId, UrlFormat = Experimentals.Subclassing_Url)]
+    [Experimental(Experimentals.Tasks_DiagnosticId, UrlFormat = Experimentals.Tasks_Url)]
     protected McpClient()
     {
     }

src/ModelContextProtocol.Core/Client/McpClientImpl.cs

@@ -6,9 +6,10 @@
 namespace ModelContextProtocol.Client;
 
 /// <inheritdoc/>
-#pragma warning disable MCPEXP002 // Subclassing McpClient is experimental
+#pragma warning disable MCPEXP001
 internal sealed partial class McpClientImpl : McpClient
 {
+#pragma warning restore MCPEXP001
     private static Implementation DefaultImplementation { get; } = new()
     {
         Name = AssemblyNameHelper.DefaultAssemblyName.Name ?? nameof(McpClient),

src/ModelContextProtocol.Core/Server/DestinationBoundMcpServer.cs

@@ -3,9 +3,9 @@
 
 namespace ModelContextProtocol.Server;
 
-#pragma warning disable MCPEXP002 // Subclassing McpServer is experimental
+#pragma warning disable MCPEXP001
 internal sealed class DestinationBoundMcpServer(McpServerImpl server, ITransport? transport) : McpServer
-#pragma warning restore MCPEXP002
+#pragma warning restore MCPEXP001
 {
     public override string? SessionId => transport?.SessionId ?? server.SessionId;
     public override string? NegotiatedProtocolVersion => server.NegotiatedProtocolVersion;

src/ModelContextProtocol.Core/Server/McpServer.cs

@@ -11,7 +11,7 @@ public abstract partial class McpServer : McpSession
     /// <summary>
     /// Initializes a new instance of the <see cref="McpServer"/> class.
     /// </summary>
-    [Experimental(Experimentals.Subclassing_DiagnosticId, UrlFormat = Experimentals.Subclassing_Url)]
+    [Experimental(Experimentals.Tasks_DiagnosticId, UrlFormat = Experimentals.Tasks_Url)]
     protected McpServer()
     {
     }

src/ModelContextProtocol.Core/Server/McpServerImpl.cs

@@ -9,9 +9,10 @@
 namespace ModelContextProtocol.Server;
 
 /// <inheritdoc />
-#pragma warning disable MCPEXP002 // Subclassing McpServer is experimental
+#pragma warning disable MCPEXP001
 internal sealed partial class McpServerImpl : McpServer
 {
+#pragma warning restore MCPEXP001
     internal static Implementation DefaultImplementation { get; } = new()
     {
         Name = AssemblyNameHelper.DefaultAssemblyName.Name ?? nameof(McpServer),

tests/ModelContextProtocol.Tests/Server/McpServerTests.cs

@@ -943,9 +943,9 @@ private static async Task InitializeServerAsync(TestServerTransport transport, C
         await tcs.Task.WaitAsync(TestConstants.DefaultTimeout, cancellationToken);
     }
 
-#pragma warning disable MCPEXP002 // Subclassing McpServer is experimental
+#pragma warning disable MCPEXP001
     private sealed class TestServerForIChatClient(bool supportsSampling) : McpServer
-#pragma warning restore MCPEXP002
+#pragma warning restore MCPEXP001
     {
         public override ClientCapabilities? ClientCapabilities =>
             supportsSampling ? new ClientCapabilities { Sampling = new SamplingCapability() } :