Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/Server/DelegatingMcpServerTool.cs

@@ -0,0 +1,33 @@
+using ModelContextProtocol.Protocol;
+
+namespace ModelContextProtocol.Server;
+
+/// <summary>Provides an <see cref="McpServerTool"/> that delegates all operations to an inner <see cref="McpServerTool"/>.</summary>
+/// <remarks>
+/// This is recommended as a base type when building tools that can be chained around an underlying <see cref="McpServerTool"/>.
+/// The default implementation simply passes each call to the inner tool instance.
+/// </remarks>
+public abstract class DelegatingMcpServerTool : McpServerTool
+{
+    private readonly McpServerTool _innerTool;
+
+    /// <summary>Initializes a new instance of the <see cref="DelegatingMcpServerTool"/> class around the specified <paramref name="innerTool"/>.</summary>
+    /// <param name="innerTool">The inner tool wrapped by this delegating tool.</param>
+    protected DelegatingMcpServerTool(McpServerTool innerTool)
+    {
+        Throw.IfNull(innerTool);
+        _innerTool = innerTool;
+    }
+
+    /// <inheritdoc />
+    public override Tool ProtocolTool => _innerTool.ProtocolTool;
+
+    /// <inheritdoc />
+    public override ValueTask<CallToolResponse> InvokeAsync(
+        RequestContext<CallToolRequestParams> request, 
+        CancellationToken cancellationToken = default) =>
+        _innerTool.InvokeAsync(request, cancellationToken);
+
+    /// <inheritdoc />
+    public override string ToString() => _innerTool.ToString();
+}