[NOMERGE] Testing for child-reaping issue

src/Http/Http.Extensions/test/JsonOptionsTests.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Runtime.InteropServices;
 using System.Text.Json.Serialization.Metadata;
 using Microsoft.AspNetCore.Http.Json;
 using Microsoft.AspNetCore.InternalTesting;
@@ -14,6 +15,38 @@ public class JsonOptionsTests
     [RemoteExecutionSupported]
     public void DefaultSerializerOptions_SetsTypeInfoResolverEmptyResolver_WhenJsonIsReflectionEnabledByDefaultFalse()
     {
+        // Diagnostic: log native libraries and threads in the testhost process
+        // to help diagnose intermittent ECHILD FailFast (dotnet/runtime#33297)
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+        {
+            try
+            {
+                Console.WriteLine("=== DIAGNOSTIC: /proc/self/maps (native libraries) ===");
+                foreach (var line in File.ReadLines("/proc/self/maps"))
+                {
+                    // Only log lines with .so files to reduce noise
+                    if (line.Contains(".so"))
+                    {
+                        Console.WriteLine(line);
+                    }
+                }
+                Console.WriteLine("=== DIAGNOSTIC: /proc/self/status ===");
+                Console.WriteLine(File.ReadAllText("/proc/self/status"));
+                Console.WriteLine("=== DIAGNOSTIC: threads ===");
+                foreach (var dir in Directory.GetDirectories("/proc/self/task"))
+                {
+                    var tid = Path.GetFileName(dir);
+                    var comm = File.ReadAllText(Path.Combine(dir, "comm")).Trim();
+                    Console.WriteLine($"  tid={tid} comm={comm}");
+                }
+                Console.WriteLine("=== END DIAGNOSTIC ===");
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"Diagnostic failed: {ex.Message}");
+            }
+        }
+
         var options = new RemoteInvokeOptions();
         options.RuntimeConfigurationOptions.Add("System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault", false.ToString());