Add cross-process mutex and retry logic for VS Setup Configuration COM API

The VS Setup Configuration COM API (ISetupConfiguration2) has a known
concurrency bug that causes failures (exit code 57005/0xDEAD) when
multiple processes enumerate VS instances simultaneously. This hits
template engine integration tests that run dotnet new in parallel.

The previous fix (PR #44930) added an in-process lock (s_guard) but
that doesn't help when multiple test processes call the API concurrently.

This fix adds:
- A named system mutex (Global\DotNetSdk_VSSetupConfiguration) to
  serialize cross-process access to the COM API
- Retry logic with exponential backoff (3 attempts) as a safety net
  for cases where external processes also call the API without our mutex

Fixes #44878

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MichaelSimons

src/Cli/dotnet/Commands/Workload/List/VisualStudioWorkloads.cs

@@ -23,6 +23,23 @@ internal static class VisualStudioWorkloads
 {
     private static readonly object s_guard = new();
 
+    /// <summary>
+    /// Named mutex used to serialize cross-process access to the VS Setup Configuration COM API,
+    /// which is not safe for concurrent calls from multiple processes.
+    /// See https://github.com/dotnet/sdk/issues/44878
+    /// </summary>
+    private const string VsSetupConfigurationMutexName = @"Global\DotNetSdk_VSSetupConfiguration";
+
+    /// <summary>
+    /// Maximum number of retry attempts when the COM API fails due to concurrent access.
+    /// </summary>
+    private const int MaxRetryAttempts = 3;
+
+    /// <summary>
+    /// Base delay in milliseconds between retry attempts (doubled on each retry).
+    /// </summary>
+    private const int RetryBaseDelayMs = 100;
+
     /// <summary>
     /// Visual Studio product ID filters. We dont' want to query SKUs such as Server, TeamExplorer, TestAgent
     /// TestController and BuildTools.
@@ -105,6 +122,55 @@ internal static unsafe void GetInstalledWorkloads(
         IWorkloadResolver workloadResolver,
         InstalledWorkloadsCollection installedWorkloads,
         SdkFeatureBand? sdkFeatureBand = null)
+    {
+        // Use a named mutex to serialize cross-process access to the VS Setup Configuration COM API.
+        // The API has a known concurrency bug that causes failures (exit code 57005/0xDEAD) when
+        // multiple processes enumerate VS instances simultaneously.
+        // See https://github.com/dotnet/sdk/issues/44878 and https://dev.azure.com/devdiv/DevDiv/_workitems/edit/2241752
+        using var mutex = new Mutex(initiallyOwned: false, VsSetupConfigurationMutexName);
+
+        for (int attempt = 0; attempt <= MaxRetryAttempts; attempt++)
+        {
+            try
+            {
+                // Wait up to 30 seconds to acquire the mutex. If we can't acquire it,
+                // proceed anyway (best-effort serialization).
+                bool acquired = false;
+                try
+                {
+                    acquired = mutex.WaitOne(TimeSpan.FromSeconds(30));
+                }
+                catch (AbandonedMutexException)
+                {
+                    // Another process crashed while holding the mutex - we now own it.
+                    acquired = true;
+                }
+
+                try
+                {
+                    GetInstalledWorkloadsCore(workloadResolver, installedWorkloads, sdkFeatureBand);
+                    return;
+                }
+                finally
+                {
+                    if (acquired)
+                    {
+                        mutex.ReleaseMutex();
+                    }
+                }
+            }
+            catch (Exception) when (attempt < MaxRetryAttempts)
+            {
+                // Retry with exponential backoff for transient COM failures.
+                Thread.Sleep(RetryBaseDelayMs * (1 << attempt));
+            }
+        }
+    }
+
+    private static unsafe void GetInstalledWorkloadsCore(
+        IWorkloadResolver workloadResolver,
+        InstalledWorkloadsCollection installedWorkloads,
+        SdkFeatureBand? sdkFeatureBand)
     {
         if (!ComClassFactory.TryCreate(CLSID.SetupConfiguration, out ComClassFactory? factory, out HRESULT result))
         {