From 95711fa90910997c01c240ad2e36c793ea8491bb Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 18 Jun 2026 16:12:19 +0000
Subject: [PATCH 1/3] Initial plan


From 4a70bedc52884aa0361648c21f97dabd2cbe68eb Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 18 Jun 2026 16:15:32 +0000
Subject: [PATCH 2/3] Default desktop MSBuild to process-arch (amd64/arm64)
 binary

---
 eng/common/tools.ps1 | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/eng/common/tools.ps1 b/eng/common/tools.ps1
index de32a6da377..c8e3dd7f304 100644
--- a/eng/common/tools.ps1
+++ b/eng/common/tools.ps1
@@ -432,11 +432,33 @@ function InitializeVisualStudioMSBuild([object]$vsRequirements = $null) {
   $msbuildVersionDir = if ([int]$vsMajorVersion -lt 16) { "$vsMajorVersion.0" } else { "Current" }
 
   $local:BinFolder = Join-Path $vsInstallDir "MSBuild\$msbuildVersionDir\Bin"
-  $local:Prefer64bit = if (Get-Member -InputObject $vsRequirements -Name 'Prefer64bit') { $vsRequirements.Prefer64bit } else { $false }
-  if ($local:Prefer64bit -and (Test-Path(Join-Path $local:BinFolder "amd64"))) {
-    $global:_MSBuildExe = Join-Path $local:BinFolder "amd64\msbuild.exe"
-  } else {
-    $global:_MSBuildExe = Join-Path $local:BinFolder "msbuild.exe"
+
+  # By default, use the MSBuild matching the host's process architecture (e.g. amd64 or arm64),
+  # falling back to the 32-bit MSBuild in the root Bin folder when no matching subfolder exists.
+  # The 'Prefer64bit' opt-out can be set to false to force the 32-bit MSBuild.
+  $local:Prefer64bit = if (Get-Member -InputObject $vsRequirements -Name 'Prefer64bit') { $vsRequirements.Prefer64bit } else { $true }
+
+  # Determine the architecture of the current process, accounting for a 32-bit process
+  # running on a 64-bit OS (PROCESSOR_ARCHITEW6432 holds the real machine architecture).
+  $local:ProcessArchitecture = $env:PROCESSOR_ARCHITECTURE
+  if (($local:ProcessArchitecture -eq 'x86') -and ($env:PROCESSOR_ARCHITEW6432)) {
+    $local:ProcessArchitecture = $env:PROCESSOR_ARCHITEW6432
+  }
+
+  # Map the architecture to the corresponding MSBuild subfolder. The 32-bit MSBuild lives in the
+  # root Bin folder, so x86 maps to an empty subfolder.
+  $local:MSBuildArchSubFolder = switch ($local:ProcessArchitecture) {
+    'AMD64' { 'amd64' }
+    'ARM64' { 'arm64' }
+    default { '' }
+  }
+
+  $global:_MSBuildExe = Join-Path $local:BinFolder "msbuild.exe"
+  if ($local:Prefer64bit -and $local:MSBuildArchSubFolder) {
+    $local:ArchMSBuildExe = Join-Path $local:BinFolder (Join-Path $local:MSBuildArchSubFolder "msbuild.exe")
+    if (Test-Path $local:ArchMSBuildExe) {
+      $global:_MSBuildExe = $local:ArchMSBuildExe
+    }
   }
 
   return $global:_MSBuildExe

From a45b70ca37a86d9caafb77e42b5302e00bcbcc27 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 18 Jun 2026 16:19:33 +0000
Subject: [PATCH 3/3] Remove Prefer64bit switch; always select arch-appropriate
 MSBuild

---
 eng/common/tools.ps1 | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/eng/common/tools.ps1 b/eng/common/tools.ps1
index c8e3dd7f304..32bbd183552 100644
--- a/eng/common/tools.ps1
+++ b/eng/common/tools.ps1
@@ -433,10 +433,8 @@ function InitializeVisualStudioMSBuild([object]$vsRequirements = $null) {
 
   $local:BinFolder = Join-Path $vsInstallDir "MSBuild\$msbuildVersionDir\Bin"
 
-  # By default, use the MSBuild matching the host's process architecture (e.g. amd64 or arm64),
+  # Use the MSBuild matching the host's process architecture (e.g. amd64 or arm64),
   # falling back to the 32-bit MSBuild in the root Bin folder when no matching subfolder exists.
-  # The 'Prefer64bit' opt-out can be set to false to force the 32-bit MSBuild.
-  $local:Prefer64bit = if (Get-Member -InputObject $vsRequirements -Name 'Prefer64bit') { $vsRequirements.Prefer64bit } else { $true }
 
   # Determine the architecture of the current process, accounting for a 32-bit process
   # running on a 64-bit OS (PROCESSOR_ARCHITEW6432 holds the real machine architecture).
@@ -454,7 +452,7 @@ function InitializeVisualStudioMSBuild([object]$vsRequirements = $null) {
   }
 
   $global:_MSBuildExe = Join-Path $local:BinFolder "msbuild.exe"
-  if ($local:Prefer64bit -and $local:MSBuildArchSubFolder) {
+  if ($local:MSBuildArchSubFolder) {
     $local:ArchMSBuildExe = Join-Path $local:BinFolder (Join-Path $local:MSBuildArchSubFolder "msbuild.exe")
     if (Test-Path $local:ArchMSBuildExe) {
       $global:_MSBuildExe = $local:ArchMSBuildExe