Align the 2026-07-28 wire with spec PR #3002 and SEP-2575 HTTP statuses (#1752)

Co-authored-by: Stephen Halter <halter73@gmail.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: tarekgh <tarek.mahmoud.sayed@gmail.com>

tests/ModelContextProtocol.ConformanceServer/Program.cs

@@ -73,6 +73,7 @@ public class Program
             .WithTools<ConformanceTools>()
             .WithTools<ConformanceTaskTools>()
             .WithTools<IncompleteResultTools>()
+            .WithTools<Sep2575DiagnosticTools>()
             .WithTools([ConformanceTools.CreateJsonSchema202012Tool()])
             .WithRequestFilters(filters => filters.AddCallToolFilter(next => async (request, cancellationToken) =>
             {

tests/ModelContextProtocol.ConformanceServer/Tools/Sep2575DiagnosticTools.cs

@@ -0,0 +1,62 @@
+using ModelContextProtocol;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+using System.ComponentModel;
+
+namespace ConformanceServer.Tools;
+
+/// <summary>
+/// Diagnostic tools exercised by the SEP-2575 <c>server-stateless</c> conformance scenario. Each
+/// tool exists so the harness can observe a framework behavior (capability enforcement, response
+/// stream discipline, per-request log gating) that plain application tools never trigger.
+/// </summary>
+[McpServerToolType]
+public class Sep2575DiagnosticTools
+{
+    /// <summary>
+    /// Requires the client to have declared the <c>sampling</c> capability in the per-request
+    /// <c>_meta/io.modelcontextprotocol/clientCapabilities</c>. Used to verify the server rejects
+    /// undeclared-capability calls with MissingRequiredClientCapabilityError (-32021).
+    /// </summary>
+    [McpServerTool(Name = "test_missing_capability")]
+    [Description("Requires the sampling client capability; used to verify MissingRequiredClientCapabilityError (-32021) (SEP-2575)")]
+    public static string MissingCapability(RequestContext<CallToolRequestParams> context)
+    {
+        if (context.Server.ClientCapabilities?.Sampling is not null)
+        {
+            return "Client declared the sampling capability; tool executed.";
+        }
+
+        throw new MissingRequiredClientCapabilityException(
+            new ClientCapabilities { Sampling = new() },
+            "sampling capability required but not declared by client");
+    }
+
+    /// <summary>
+    /// Returns a plain result. Per SEP-2575 the response stream must carry no independent top-level
+    /// JSON-RPC requests; a plain response trivially satisfies this. The scenario declares no
+    /// elicitation capability, so this tool must not initiate an elicitation.
+    /// </summary>
+    [McpServerTool(Name = "test_streaming_elicitation")]
+    [Description("Streams only result frames; used to verify response streams carry no independent JSON-RPC requests (SEP-2575)")]
+    public static string StreamingElicitation()
+    {
+        return "stream observed: result frames only, no top-level requests";
+    }
+
+    /// <summary>
+    /// Attempts to emit a log message through the client-logger pipeline, which gates on the
+    /// per-request <c>_meta/io.modelcontextprotocol/logLevel</c>. When the client did not opt in,
+    /// no notifications/message may be sent for the request.
+    /// </summary>
+    [McpServerTool(Name = "test_logging_tool")]
+    [Description("Attempts to emit a log message; the framework must drop it when the client did not set _meta.../logLevel (SEP-2575)")]
+    public static string LoggingTool(RequestContext<CallToolRequestParams> context)
+    {
+#pragma warning disable MCP9004 // AsClientLoggerProvider is deprecated with the legacy logging/setLevel flow but remains the gated client-log pipeline.
+        ILogger logger = context.Server.AsClientLoggerProvider().CreateLogger(nameof(Sep2575DiagnosticTools));
+#pragma warning restore MCP9004
+        logger.LogInformation("test_logging_tool executed");
+        return "Log attempted; framework gates on _meta.../logLevel.";
+    }
+}