Address feedback and CI failure

Author: ericstj

src/ModelContextProtocol.Core/Client/StdioClientSessionTransport.cs

@@ -48,16 +48,12 @@ public override async Task SendMessageAsync(JsonRpcMessage message, Cancellation
     protected override async ValueTask CleanupAsync(Exception? error = null, CancellationToken cancellationToken = default)
     {
         // Only run the full stdio cleanup once (handler detach, process kill, etc.).
-        // But always call base.CleanupAsync — it cancels the shutdown CTS (which
-        // unblocks the primary path if it's stuck in WaitForExitAsync), waits for
-        // the read task to complete (so the primary path can call SetDisconnected
-        // with full StdioClientCompletionDetails), and calls SetDisconnected itself
-        // as a fallback. We wrap the error in TransportClosedException so the
-        // fallback SetDisconnected still produces StdioClientCompletionDetails
-        // rather than a bare ClientCompletionDetails.
+        // If another call is already handling cleanup, cancel the shutdown token
+        // to unblock it (e.g. if it's stuck in WaitForExitAsync) and let it
+        // call SetDisconnected with full StdioClientCompletionDetails.
         if (Interlocked.Exchange(ref _cleanedUp, 1) != 0)
         {
-            await base.CleanupAsync(new TransportClosedException(BuildCompletionDetails(error)), cancellationToken).ConfigureAwait(false);
+            CancelShutdown();
             return;
         }
 

src/ModelContextProtocol.Core/Client/StdioClientTransport.cs

@@ -137,7 +137,7 @@ public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken =
             // few lines in a rolling log for use in exceptions.
             const int MaxStderrLength = 10; // keep the last 10 lines of stderr
             Queue<string> stderrRollingLog = new(MaxStderrLength);
-            process.ErrorDataReceived += errorHandler = (sender, args) =>
+            errorHandler = (sender, args) =>
             {
                 string? data = args.Data;
                 if (data is not null)
@@ -167,6 +167,7 @@ public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken =
                     LogReadStderr(logger, endpointName, data);
                 }
             };
+            process.ErrorDataReceived += errorHandler;
 
             // We need both stdin and stdout to use a no-BOM UTF-8 encoding. On .NET Core,
             // we can use ProcessStartInfo.StandardOutputEncoding/StandardInputEncoding, but

src/ModelContextProtocol.Core/Client/StreamClientSessionTransport.cs

@@ -164,6 +164,21 @@ private async Task ProcessMessageAsync(string line, CancellationToken cancellati
         }
     }
 
+    /// <summary>
+    /// Cancels the shutdown token to signal that the transport is shutting down,
+    /// without performing any other cleanup.
+    /// </summary>
+    protected void CancelShutdown()
+    {
+        try
+        {
+            _shutdownCts?.Cancel();
+        }
+        catch (ObjectDisposedException)
+        {
+        }
+    }
+
     protected virtual async ValueTask CleanupAsync(Exception? error = null, CancellationToken cancellationToken = default)
     {
         LogTransportShuttingDown(Name);