Fix Metadata delegation in DelegatingMcpServerTool/Prompt/Resource (#1338)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>

tests/ModelContextProtocol.Tests/Server/DelegatingMcpServerPromptTests.cs

@@ -0,0 +1,58 @@
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+using System.Reflection;
+
+namespace ModelContextProtocol.Tests.Server;
+
+public class DelegatingMcpServerPromptTests
+{
+    [Fact]
+    public void Ctor_NullInnerPrompt_Throws()
+    {
+        Assert.Throws<ArgumentNullException>("innerPrompt", () => new TestDelegatingPrompt(null!));
+    }
+
+    [Fact]
+    public async Task AllMembers_DelegateToInnerPrompt()
+    {
+        Prompt expectedPrompt = new() { Name = "sentinel-prompt" };
+        IReadOnlyList<object> expectedMetadata = new object[] { "m1" };
+        GetPromptResult expectedResult = new() { Messages = [] };
+        InnerPrompt inner = new(expectedPrompt, expectedMetadata, expectedResult);
+
+        TestDelegatingPrompt delegating = new(inner);
+
+        Assert.Same(expectedPrompt, delegating.ProtocolPrompt);
+        Assert.Same(expectedMetadata, delegating.Metadata);
+        Assert.Same(expectedResult, await delegating.GetAsync(null!, CancellationToken.None));
+        Assert.Equal(inner.ToString(), delegating.ToString());
+    }
+
+    [Fact]
+    public void OverridesAllVirtualAndAbstractMembers()
+    {
+        MethodInfo[] baseMethods = typeof(McpServerPrompt).GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)
+            .Where(m => m.IsVirtual || m.IsAbstract)
+            .ToArray();
+
+        Assert.NotEmpty(baseMethods);
+
+        foreach (MethodInfo baseMethod in baseMethods)
+        {
+            Assert.True(
+                typeof(DelegatingMcpServerPrompt).GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)
+                    .Any(m => m.Name == baseMethod.Name),
+                $"DelegatingMcpServerPrompt does not override {baseMethod.Name} from McpServerPrompt.");
+        }
+    }
+
+    private sealed class TestDelegatingPrompt(McpServerPrompt innerPrompt) : DelegatingMcpServerPrompt(innerPrompt);
+
+    private sealed class InnerPrompt(Prompt protocolPrompt, IReadOnlyList<object> metadata, GetPromptResult result) : McpServerPrompt
+    {
+        public override Prompt ProtocolPrompt => protocolPrompt;
+        public override IReadOnlyList<object> Metadata => metadata;
+        public override ValueTask<GetPromptResult> GetAsync(RequestContext<GetPromptRequestParams> request, CancellationToken cancellationToken = default) => new(result);
+        public override string ToString() => "inner-prompt";
+    }
+}