Fix merge conflicts and address PR feedback

- Catch and log errors
- Send _negotiatedProtocolVersion

Author: halter73

src/ModelContextProtocol.Core/Client/SseClientSessionTransport.cs

@@ -91,7 +91,7 @@ public override async Task SendMessageAsync(
         {
             Content = content,
         };
-        StreamableHttpClientSessionTransport.CopyAdditionalHeaders(httpRequestMessage.Headers, _options.AdditionalHeaders);
+        StreamableHttpClientSessionTransport.CopyAdditionalHeaders(httpRequestMessage.Headers, _options.AdditionalHeaders, sessionId: null, protocolVersion: null);
         var response = await _httpClient.SendAsync(httpRequestMessage, cancellationToken).ConfigureAwait(false);
 
         if (!response.IsSuccessStatusCode)
@@ -152,7 +152,7 @@ private async Task ReceiveMessagesAsync(CancellationToken cancellationToken)
         {
             using var request = new HttpRequestMessage(HttpMethod.Get, _sseEndpoint);
             request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("text/event-stream"));
-            StreamableHttpClientSessionTransport.CopyAdditionalHeaders(request.Headers, _options.AdditionalHeaders);
+            StreamableHttpClientSessionTransport.CopyAdditionalHeaders(request.Headers, _options.AdditionalHeaders, sessionId: null, protocolVersion: null);
 
             using var response = await _httpClient.SendAsync(
                 request,

src/ModelContextProtocol.Core/Client/StreamableHttpClientSessionTransport.cs

@@ -145,13 +145,9 @@ public override async ValueTask DisposeAsync()
             try
             {
                 // Send DELETE request to terminate the session only send if we have a session ID per MCP spec
-                if (!string.IsNullOrEmpty(_mcpSessionId))
+                if (!string.IsNullOrEmpty(SessionId))
                 {
-                    using var deleteRequest = new HttpRequestMessage(HttpMethod.Delete, _options.Endpoint);
-                    CopyAdditionalHeaders(deleteRequest.Headers, _options.AdditionalHeaders, _mcpSessionId);
-
-                    // Do not validate we get a successful status code, because server support for the DELETE request is optional
-                    using var deleteResponse = await _httpClient.SendAsync(deleteRequest, CancellationToken.None).ConfigureAwait(false);
+                    await SendDeleteRequest();
                 }
 
                 if (_getReceiveTask != null)
@@ -246,6 +242,22 @@ message is JsonRpcMessageWithId rpcResponseOrError &&
         return null;
     }
 
+    private async Task SendDeleteRequest()
+    {
+        using var deleteRequest = new HttpRequestMessage(HttpMethod.Delete, _options.Endpoint);
+        CopyAdditionalHeaders(deleteRequest.Headers, _options.AdditionalHeaders, SessionId, _negotiatedProtocolVersion);
+
+        try
+        {
+            // Do not validate we get a successful status code, because server support for the DELETE request is optional
+            (await _httpClient.SendAsync(deleteRequest, CancellationToken.None).ConfigureAwait(false)).Dispose();
+        }
+        catch (Exception ex)
+        {
+            LogTransportShutdownFailed(Name, ex);
+        }
+    }
+
     private void LogJsonException(JsonException ex, string data)
     {
         if (_logger.IsEnabled(LogLevel.Trace))
@@ -261,8 +273,8 @@ private void LogJsonException(JsonException ex, string data)
     internal static void CopyAdditionalHeaders(
         HttpRequestHeaders headers,
         IDictionary<string, string>? additionalHeaders,
-        string? sessionId = null,
-        string? protocolVersion = null)
+        string? sessionId,
+        string? protocolVersion)
     {
         if (sessionId is not null)
         {

tests/ModelContextProtocol.AspNetCore.Tests/Utils/KestrelInMemoryConnection.cs

@@ -81,7 +81,7 @@ public override Task FlushAsync(CancellationToken cancellationToken)
         protected override void Dispose(bool disposing)
         {
             // Signal to the server the the client has closed the connection, and dispose the client-half of the Pipes.
-            connectionClosedCts.Cancel();
+            ThreadPool.UnsafeQueueUserWorkItem(static cts => ((CancellationTokenSource)cts!).Cancel(), connectionClosedCts);
             duplexPipe.Input.Complete();
             duplexPipe.Output.Complete();
         }