Preserve credential provider logo transparency

scripts/Install-CredentialProvider.ps1

@@ -123,7 +123,18 @@ finally {
 $versionId = $packageHash.Substring(0, 16)
 $installPath = Join-Path $installRoot "versions\$versionId"
 $completeMarker = Join-Path $installPath '.complete'
-if ((Test-Path -LiteralPath $installPath) -and -not (Test-Path -LiteralPath $completeMarker)) {
+$completeMarkerValid = $false
+if (Test-Path -LiteralPath $completeMarker -PathType Leaf) {
+    try {
+        $completeMarkerValid = [IO.File]::ReadAllText($completeMarker).Trim() -eq $packageHash
+    }
+    catch {
+        # Treat an unreadable marker as an incomplete installation. Never reuse
+        # a version directory unless its marker proves that every package byte
+        # represented by packageHash finished installing.
+    }
+}
+if ((Test-Path -LiteralPath $installPath) -and -not $completeMarkerValid) {
     $installPath = '{0}-{1}' -f $installPath, ([Guid]::NewGuid().ToString('N').Substring(0, 8))
     $completeMarker = Join-Path $installPath '.complete'
 }