Guard Trace logging calls with IsEnabled check

Wrap logging calls with Logger.IsEnabled(LogLevel.Trace) to avoid
expensive JSON serialization when trace logging is not enabled.

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

src/ModelContextProtocol.Core/Client/SseClientSessionTransport.cs

@@ -80,7 +80,10 @@ public override async Task SendMessageAsync(
             messageId = messageWithId.Id.ToString();
         }
 
-        LogTransportSendingMessageSensitive(Name, JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage));
+        if (_logger.IsEnabled(LogLevel.Trace))
+        {
+            LogTransportSendingMessageSensitive(Name, JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage));
+        }
 
         using var httpRequestMessage = new HttpRequestMessage(HttpMethod.Post, _messageEndpoint);
         StreamableHttpClientSessionTransport.CopyAdditionalHeaders(httpRequestMessage.Headers, _options.AdditionalHeaders, sessionId: null, protocolVersion: null);

src/ModelContextProtocol.Core/Client/StreamClientSessionTransport.cs

@@ -105,7 +105,10 @@ public override async Task SendMessageAsync(JsonRpcMessage message, Cancellation
 
         var json = JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage);
 
-        LogTransportSendingMessageSensitive(Name, json);
+        if (Logger.IsEnabled(LogLevel.Trace))
+        {
+            LogTransportSendingMessageSensitive(Name, json);
+        }
 
         using var _ = await _sendLock.LockAsync(cancellationToken).ConfigureAwait(false);
         try

src/ModelContextProtocol.Core/Client/StreamableHttpClientSessionTransport.cs

@@ -75,7 +75,10 @@ internal async Task<HttpResponseMessage> SendHttpRequestAsync(JsonRpcMessage mes
                 $"Call {nameof(McpClient)}.{nameof(McpClient.ResumeSessionAsync)} to resume existing sessions.");
         }
 
-        LogTransportSendingMessageSensitive(Name, JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage));
+        if (_logger.IsEnabled(LogLevel.Trace))
+        {
+            LogTransportSendingMessageSensitive(Name, JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage));
+        }
 
         using var sendCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, _connectionCts.Token);
         cancellationToken = sendCts.Token;

src/ModelContextProtocol.Core/Server/StreamServerTransport.cs

@@ -75,7 +75,10 @@ public override async Task SendMessageAsync(JsonRpcMessage message, Cancellation
         try
         {
             var json = JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage);
-            LogTransportSendingMessageSensitive(Name, json);
+            if (Logger.IsEnabled(LogLevel.Trace))
+            {
+                LogTransportSendingMessageSensitive(Name, json);
+            }
             await _outputStream.WriteAsync(Encoding.UTF8.GetBytes(json), cancellationToken).ConfigureAwait(false);
             await _outputStream.WriteAsync(s_newlineBytes, cancellationToken).ConfigureAwait(false);
             await _outputStream.FlushAsync(cancellationToken).ConfigureAwait(false);