diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e4bebe2..6ca6d51 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,6 +36,11 @@ jobs:
         shell: pwsh
         run: ./skills/scripts/test-bootstrap-supply-chain.ps1
 
+      - name: Bootstrap supply-chain regression (Windows PowerShell 5.1)
+        if: runner.os == 'Windows'
+        shell: powershell
+        run: ./skills/scripts/test-bootstrap-supply-chain.ps1
+
       - name: Smoke (verify + parse + quick route)
         shell: pwsh
         run: ./skills/scripts/smoke.ps1
diff --git a/skills/scripts/lib/BootstrapSupplyChain.ps1 b/skills/scripts/lib/BootstrapSupplyChain.ps1
index 6e6c4c8..36dbd27 100644
--- a/skills/scripts/lib/BootstrapSupplyChain.ps1
+++ b/skills/scripts/lib/BootstrapSupplyChain.ps1
@@ -4,8 +4,17 @@ function Ensure-Pnpm {
     $pnpm = Get-NodeCommandPath -Name 'pnpm'
     $currentVersion = ''
     if ($pnpm) {
-        $versionLine = & $pnpm --version 2>$null | Select-Object -First 1
-        if ($LASTEXITCODE -eq 0 -and $null -ne $versionLine) {
+        $previousErrorActionPreference = $ErrorActionPreference
+        try {
+            $ErrorActionPreference = 'Continue'
+            $versionOutput = @(& $pnpm --version 2>$null)
+            $versionExitCode = $LASTEXITCODE
+        }
+        finally {
+            $ErrorActionPreference = $previousErrorActionPreference
+        }
+        $versionLine = $versionOutput | Select-Object -First 1
+        if ($versionExitCode -eq 0 -and $null -ne $versionLine) {
             $currentVersion = ([string]$versionLine).Trim()
         }
     }
@@ -28,13 +37,29 @@ function Assert-GitCheckoutState {
         [Parameter(Mandatory = $true)][string]$PinnedCommit
     )
 
-    $resolvedLine = & $GitPath -C $CheckoutPath rev-parse HEAD 2>$null | Select-Object -First 1
+    $previousErrorActionPreference = $ErrorActionPreference
+    try {
+        $ErrorActionPreference = 'Continue'
+        $resolvedOutput = @(& $GitPath -C $CheckoutPath rev-parse HEAD 2>$null)
+        $resolveExitCode = $LASTEXITCODE
+    }
+    finally {
+        $ErrorActionPreference = $previousErrorActionPreference
+    }
+    $resolvedLine = $resolvedOutput | Select-Object -First 1
     $resolvedCommit = if ($null -eq $resolvedLine) { '' } else { ([string]$resolvedLine).Trim() }
-    if ($LASTEXITCODE -ne 0 -or $resolvedCommit -ne $PinnedCommit) {
+    if ($resolveExitCode -ne 0 -or $resolvedCommit -ne $PinnedCommit) {
         throw "Checkout verification failed: expected $PinnedCommit, got $resolvedCommit ($CheckoutPath)"
     }
-    $status = @(& $GitPath -C $CheckoutPath status --porcelain --untracked-files=all 2>&1)
-    if ($LASTEXITCODE -ne 0) {
+    try {
+        $ErrorActionPreference = 'Continue'
+        $status = @(& $GitPath -C $CheckoutPath status --porcelain --untracked-files=all 2>$null)
+        $statusExitCode = $LASTEXITCODE
+    }
+    finally {
+        $ErrorActionPreference = $previousErrorActionPreference
+    }
+    if ($statusExitCode -ne 0) {
         throw "Cannot inspect checkout state: $CheckoutPath"
     }
     if ($status.Count -gt 0) {
diff --git a/skills/scripts/test-bootstrap-supply-chain.ps1 b/skills/scripts/test-bootstrap-supply-chain.ps1
index a6723f8..0647a46 100644
--- a/skills/scripts/test-bootstrap-supply-chain.ps1
+++ b/skills/scripts/test-bootstrap-supply-chain.ps1
@@ -64,7 +64,7 @@ try {
     New-Item -ItemType Directory -Path $bin | Out-Null
     $env:PATH = "$bin$([IO.Path]::PathSeparator)$env:PATH"
     $env:BOOTSTRAP_PS_LOG = Join-Path $scratch 'commands.log'
-    $isWindowsHost = $env:OS -eq 'Windows_NT'
+    $isWindowsHost = [Environment]::OSVersion.Platform -eq [PlatformID]::Win32NT
     $stub = Join-Path $bin ($(if ($isWindowsHost) { 'npm.cmd' } else { 'npm' }))
     if ($isWindowsHost) {
         Set-Content $stub @'
@@ -98,6 +98,10 @@ if "%1"=="--version" (echo 10.24.0) else (echo pnpm^|%*>>"%BOOTSTRAP_PS_LOG%")
 printf "pnpm|%s\n" "$*" >> "$BOOTSTRAP_PS_LOG"
 '@
     }
+    $commandLogBefore = Get-Content -LiteralPath $env:BOOTSTRAP_PS_LOG -Raw
+    Ensure-Pnpm
+    $commandLogAfter = Get-Content -LiteralPath $env:BOOTSTRAP_PS_LOG -Raw
+    Assert-True ($commandLogAfter -eq $commandLogBefore) 'matching pnpm version triggered reinstall'
     function Approve-AnythingAnalyzerBuildScripts { param([string]$RepoDir) Set-Content (Join-Path $RepoDir 'pnpm-workspace.yaml') 'generated'; Set-Content (Join-Path $RepoDir 'package.json') '{"mutated":true}' }
     $dirtyRejected = $false
     try { Invoke-AnythingAnalyzerPinnedInstall -RepoDir $target -PnpmPath $pnpm -GitPath (Get-Command git).Source -PinnedCommit $pin } catch { $dirtyRejected = $_.Exception.Message -match 'local changes' }