Convert VPC win64 projects to Win32 for Proton DLLs

ddiff --git a/docs/WINDOWS_VPC_WIN32_PROJECT_CONVERSION.md b/docs/WINDOWS_VPC_WIN32_PROJECT_CONVERSION.md
nnew file mode 100644
iindex 0000000..e51355c
---- /dev/null
++++ b/docs/WINDOWS_VPC_WIN32_PROJECT_CONVERSION.md
@@@ -0,0 +1,5 @@
++# Windows Win32 VPC project conversion
++
++Current Valve Source SDK 2013 VPC output on GitHub's Windows runner can still emit `*_win64_*.vcxproj` projects even when the build is relaunched through an x86 Visual Studio shell. For Proton compatibility with 32-bit Source SDK Base installs, the Windows build script converts generated vcxproj platform/config metadata to Win32 before MSBuild runs.
++
++The conversion changes project configurations from x64/Win64 to Win32, switches the linker target to MachineX86, removes 64-bit preprocessor defines, adds COMPILER_MSVC32, points public library paths back to `lib/public`, and disables warning-as-error behavior for the modern VS2022 Win32 pass.
ddiff --git a/tools/build-sdk-windows.ps1 b/tools/build-sdk-windows.ps1
iindex 3112994..236f406 100644
---- a/tools/build-sdk-windows.ps1
++++ b/tools/build-sdk-windows.ps1
@@@ -19,13 +19,13 @@ New-Item -ItemType Directory -Force -Path $LogDir | Out-Null
  function Say($m) { Write-Host "[openvibe-win] $m" }
  
  # OPENVIBE_PROTON_WIN32_DLL_TARGET
--$script:OpenVibeTargetArch = if ($env:OPENVIBE_WINDOWS_TARGET_ARCH) { $env:OPENVIBE_WINDOWS_TARGET_ARCH.ToLowerInvariant() } else { "x86" }
++$script:OpenVibeTargetArch = if ($env:OPENVIBE_WINDOWS_TARGET_ARCH) { ([string]$env:OPENVIBE_WINDOWS_TARGET_ARCH).Trim().ToLowerInvariant() } else { "x86" }
  if ($script:OpenVibeTargetArch -notin @("x86", "x64")) {
    throw "OPENVIBE_WINDOWS_TARGET_ARCH must be x86 or x64, got '$script:OpenVibeTargetArch'"
  }
  # OPENVIBE_TARGET_ARCH_NORMALIZE_AFTER_VALIDATE
--$script:TargetArch = ([string]$script:TargetArch).Trim()
--$env:OPENVIBE_WINDOWS_TARGET_ARCH = $script:TargetArch
++$script:OpenVibeTargetArch = ([string]$script:OpenVibeTargetArch).Trim().ToLowerInvariant()
++$env:OPENVIBE_WINDOWS_TARGET_ARCH = $script:OpenVibeTargetArch
  
  Write-Host "[openvibe-win] target arch=$script:OpenVibeTargetArch"
  function Require($p, $msg) {
@@@ -418,6 +418,57 @@ function Sort-PreferredConfigs($pairs, [string]$projName) {
  }
  
  
++
++
++# OPENVIBE_FORCE_WIN32_FROM_VPC_WIN64_PROJECTS
++function Convert-GeneratedVcxprojsToWin32 {
++  if ($script:OpenVibeTargetArch -ne "x86") { return }
++
++  $log = Join-Path $LogDir "win32-vcxproj-conversion.txt"
++  "target=x86" | Out-File $log
++  Say "converting VPC-generated vcxproj files from x64/win64 metadata to Win32"
++
++  $projects = @(Get-ChildItem -Path $Src -Recurse -File -Filter "*.vcxproj" -ErrorAction SilentlyContinue)
++  foreach ($proj in $projects) {
++    $text = Get-Content -Raw $proj.FullName
++    $before = $text
++
++    # Convert project configuration/platform names. VPC on current hosted runners emits win64 project files
++    # even from an x86 VS shell, so build the same project bodies as Win32.
++    $text = $text -replace '\|x64', '|Win32'
++    $text = $text -replace '\|Win64', '|Win32'
++    $text = $text -replace '<Platform>x64</Platform>', '<Platform>Win32</Platform>'
++    $text = $text -replace '<Platform>Win64</Platform>', '<Platform>Win32</Platform>'
++    $text = $text -replace '<PlatformTarget>x64</PlatformTarget>', '<PlatformTarget>x86</PlatformTarget>'
++    $text = $text -replace '<PlatformTarget>Win64</PlatformTarget>', '<PlatformTarget>x86</PlatformTarget>'
++    $text = $text -replace '<TargetMachine>MachineX64</TargetMachine>', '<TargetMachine>MachineX86</TargetMachine>'
++    $text = $text -replace 'MachineX64', 'MachineX86'
++
++    # Remove 64-bit preprocessor defines baked into the generated project and add the 32-bit one.
++    foreach ($def in @('PLATFORM_64BITS','WIN64','_WIN64','COMPILER_MSVC64')) {
++      $text = $text -replace (";" + [regex]::Escape($def) + ";"), ";"
++      $text = $text -replace ("(^|>)" + [regex]::Escape($def) + ";"), '$1'
++      $text = $text -replace (";" + [regex]::Escape($def) + "(<|$)"), '$1'
++    }
++    $text = [regex]::Replace($text, '<PreprocessorDefinitions>(?![^<]*COMPILER_MSVC32)', '<PreprocessorDefinitions>COMPILER_MSVC32;')
++    $text = $text -replace ';;+', ';'
++
++    # Make x86 link against the normal public lib folder, not lib/public/x64.
++    $text = $text -replace '\\lib\\public\\x64', '\lib\public'
++    $text = $text -replace '/lib/public/x64', '/lib/public'
++
++    # Avoid Win32 warnings-as-errors while we are building modern VS2022 against old Source SDK code.
++    $text = $text -replace '<TreatWarningAsError>true</TreatWarningAsError>', '<TreatWarningAsError>false</TreatWarningAsError>'
++    $text = $text -replace '<TreatWarningsAsErrors>true</TreatWarningsAsErrors>', '<TreatWarningsAsErrors>false</TreatWarningsAsErrors>'
++    $text = $text -replace '<TreatWarningAsError>Yes \(/WX\)</TreatWarningAsError>', '<TreatWarningAsError>false</TreatWarningAsError>'
++
++    if ($text -ne $before) {
++      Set-Content -Encoding utf8 -Path $proj.FullName -Value $text
++      "converted $($proj.FullName)" | Out-File $log -Append
++    }
++  }
++}
++
  function Patch-GeneratedPythonCustomBuildCommands {
    if (-not $script:OpenVibePythonCommand -or !(Test-Path $script:OpenVibePythonCommand)) {
      Ensure-PythonCommandForMSBuild
@@@ -469,7 +520,12 @@ function Invoke-MSBuildProject([System.IO.FileInfo]$proj, [string]$label) {
      $platSafe = ($p.Platform -replace '[^A-Za-z0-9]+','_')
      $log = Join-Path $LogDir "msbuild-$label-$cfgSafe-$platSafe.log"
      Say "msbuild $label cfg=$($p.Configuration) platform=$($p.Platform)"
--    & msbuild $proj.FullName /m /p:Configuration="$($p.Configuration)" /p:Platform="$($p.Platform)" /t:Build /v:minimal /nologo 2>&1 | Tee-Object -FilePath $log | Out-Host
++    $extraProps = @()
++    if ($script:OpenVibeTargetArch -eq "x86") {
++      $extraProps += "/p:TreatWarningsAsErrors=false"
++      $extraProps += "/p:PlatformTarget=x86"
++    }
++    & msbuild $proj.FullName /m /p:Configuration="$($p.Configuration)" /p:Platform="$($p.Platform)" @extraProps /t:Build /v:minimal /nologo 2>&1 | Tee-Object -FilePath $log | Out-Host
      if ($LASTEXITCODE -eq 0) {
        Say "built $label with cfg=$($p.Configuration) platform=$($p.Platform)"
        return $true
@@@ -552,6 +608,13 @@ if ($clientProjects.Count -eq 0 -or $serverProjects.Count -eq 0) {
    $serverProjects = @(Get-ChildItem -Path $Src -Recurse -File -Filter "*server*hl2mp*.vcxproj" -ErrorAction SilentlyContinue)
  }
  
++
++if ($script:OpenVibeTargetArch -eq "x86") {
++  Convert-GeneratedVcxprojsToWin32
++  $clientProjects = @(Get-ChildItem -Path $Src -Recurse -File -Filter "*client*hl2mp*.vcxproj" -ErrorAction SilentlyContinue)
++  $serverProjects = @(Get-ChildItem -Path $Src -Recurse -File -Filter "*server*hl2mp*.vcxproj" -ErrorAction SilentlyContinue)
++}
++
  "=== normalized solutions ===" | Out-File (Join-Path $LogDir "normalized-solutions.txt")
  $solutions | Select-Object FullName,Length,LastWriteTime | Format-List | Out-File (Join-Path $LogDir "normalized-solutions.txt") -Append
  "=== hl2mp projects ===" | Out-File (Join-Path $LogDir "hl2mp-projects.txt")