Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/Server/DelegatingMcpServerPrompt.cs

@@ -0,0 +1,33 @@
+using ModelContextProtocol.Protocol;
+
+namespace ModelContextProtocol.Server;
+
+/// <summary>Provides an <see cref="McpServerPrompt"/> that delegates all operations to an inner <see cref="McpServerPrompt"/>.</summary>
+/// <remarks>
+/// This is recommended as a base type when building prompts that can be chained around an underlying <see cref="McpServerPrompt"/>.
+/// The default implementation simply passes each call to the inner prompt instance.
+/// </remarks>
+public abstract class DelegatingMcpServerPrompt : McpServerPrompt
+{
+    private readonly McpServerPrompt _innerPrompt;
+
+    /// <summary>Initializes a new instance of the <see cref="DelegatingMcpServerPrompt"/> class around the specified <paramref name="innerPrompt"/>.</summary>
+    /// <param name="innerPrompt">The inner prompt wrapped by this delegating prompt.</param>
+    protected DelegatingMcpServerPrompt(McpServerPrompt innerPrompt)
+    {
+        Throw.IfNull(innerPrompt);
+        _innerPrompt = innerPrompt;
+    }
+
+    /// <inheritdoc />
+    public override Prompt ProtocolPrompt => _innerPrompt.ProtocolPrompt;
+
+    /// <inheritdoc />
+    public override ValueTask<GetPromptResult> GetAsync(
+        RequestContext<GetPromptRequestParams> request, 
+        CancellationToken cancellationToken = default) =>
+        _innerPrompt.GetAsync(request, cancellationToken);
+
+    /// <inheritdoc />
+    public override string ToString() => _innerPrompt.ToString();
+}