Pin the MCP conformance tester package

Directory.Packages.props

@@ -5,6 +5,8 @@
     <System9Version>9.0.11</System9Version>
     <System10Version>10.0.2</System10Version>
     <MicrosoftExtensionsVersion>10.2.0</MicrosoftExtensionsVersion>
+    <!-- Pin the conformance tester Node package version for CI stability -->
+    <McpConformanceVersion>0.1.10</McpConformanceVersion>
   </PropertyGroup>
 
   <!-- Product dependencies shared -->

tests/ModelContextProtocol.AspNetCore.Tests/ModelContextProtocol.AspNetCore.Tests.csproj

@@ -51,6 +51,13 @@
     <PackageReference Include="System.Linq.AsyncEnumerable" />
   </ItemGroup>
 
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Reflection.AssemblyMetadataAttribute">
+      <_Parameter1>McpConformanceVersion</_Parameter1>
+      <_Parameter2>$(McpConformanceVersion)</_Parameter2>
+    </AssemblyAttribute>
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\samples\TestServerWithHosting\TestServerWithHosting.csproj" />
     <ProjectReference Include="..\..\src\ModelContextProtocol.Core\ModelContextProtocol.Core.csproj" />

tests/ModelContextProtocol.AspNetCore.Tests/ServerConformanceTests.cs

@@ -115,9 +115,32 @@ private void StartConformanceServer()
         _serverTask = Task.Run(() => ConformanceServer.Program.MainAsync(["--urls", _serverUrl], new XunitLoggerProvider(_output), cancellationToken: _serverCts.Token));
     }
 
+    private static string GetConformanceVersion()
+    {
+        var assembly = typeof(ServerConformanceTests).Assembly;
+        var attribute = assembly.GetCustomAttributes(typeof(System.Reflection.AssemblyMetadataAttribute), false)
+            .Cast<System.Reflection.AssemblyMetadataAttribute>()
+            .FirstOrDefault(a => a.Key == "McpConformanceVersion");
+        return attribute?.Value ?? throw new InvalidOperationException("McpConformanceVersion not found in assembly metadata");
+    }
+
     private async Task<(bool Success, string Output, string Error)> RunNpxConformanceTests()
     {
-        var startInfo = NodeHelpers.NpxStartInfo($"-y @modelcontextprotocol/conformance server --url {_serverUrl}");
+        // Version is configured in Directory.Packages.props for central management
+        var version = GetConformanceVersion();
+        _output.WriteLine($"=== Requested conformance package version: {version} ===");
+
+        // First, check the actual version that will be used
+        var versionCheckInfo = NodeHelpers.NpxStartInfo($"-y @modelcontextprotocol/conformance@{version} --version");
+        var versionProcess = Process.Start(versionCheckInfo);
+        if (versionProcess != null)
+        {
+            var actualVersion = await versionProcess.StandardOutput.ReadToEndAsync();
+            await versionProcess.WaitForExitAsync();
+            _output.WriteLine($"=== Actual conformance package version: {actualVersion.Trim()} ===");
+        }
+
+        var startInfo = NodeHelpers.NpxStartInfo($"-y @modelcontextprotocol/conformance@{version} server --url {_serverUrl}");
 
         var outputBuilder = new StringBuilder();
         var errorBuilder = new StringBuilder();

tests/ModelContextProtocol.ConformanceServer/Program.cs

@@ -94,7 +94,8 @@ public static async Task MainAsync(string[] args, ILoggerProvider? loggerProvide
 
         app.MapMcp();
 
-        app.MapGet("/health", () => TypedResults.Ok("Healthy"));
+        // Return plain string to avoid JSON serialization issues when reflection is disabled
+        app.MapGet("/health", () => "Healthy");
 
         await app.RunAsync(cancellationToken);
     }