From 1dd06e73dc2d68e602885e45b1382127e663980c Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Sun, 15 Feb 2026 16:33:09 -0500
Subject: [PATCH] Fix stderr event loss due to missing WaitForExit in
 DisposeProcess (#1280)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
---
 .../Client/StdioClientTransport.cs                   | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/ModelContextProtocol.Core/Client/StdioClientTransport.cs b/src/ModelContextProtocol.Core/Client/StdioClientTransport.cs
index 95f5221..191a512 100644
--- a/src/ModelContextProtocol.Core/Client/StdioClientTransport.cs
+++ b/src/ModelContextProtocol.Core/Client/StdioClientTransport.cs
@@ -227,6 +227,18 @@ public sealed partial class StdioClientTransport : IClientTransport
                     // and Node.js does not kill its children when it exits properly.
                     process.KillTree(shutdownTimeout);
                 }
+
+                // Ensure all redirected stderr/stdout events have been dispatched
+                // before disposing. Only the no-arg WaitForExit() guarantees this;
+                // WaitForExit(int) (as used by KillTree) does not.
+                // This should not hang: either the process already exited on its own
+                // (no child processes holding handles), or KillTree killed the entire
+                // process tree. If it does take too long, the test infrastructure's
+                // own timeout will catch it.
+                if (!processRunning && HasExited(process))
+                {
+                    process.WaitForExit();
+                }
             }
             finally
             {