WIP: add Windows Update template with online COM API updates

Add essentials.windowsUpdate template that boots Audit Mode, uses the
Windows Update COM API to search/download/install all available updates
(cumulative, .NET, Defender), handles multi-round reboots with Audit
Mode preservation, and compacts the image afterward.

Known issues being worked:
- Audit Mode preservation after update reboot needs verification
- Install takes ~60-90 min with 4GB RAM on slow machines

See wip/win10-update.session.md for full context and TODOs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/images/windows/templates/essentials/windows-update.nix

@@ -0,0 +1,114 @@
+# Apply all available Windows Updates via the Windows Update COM API in Audit Mode.
+# Handles reboots automatically — re-registers via RunOnce and continues updating.
+# Compacts the image afterward to flatten the COW chain.
+#
+# Usage:
+#   essentials.windowsUpdate {}
+#   essentials.windowsUpdate { maxRounds = 5; }
+{ pkgs, lib, ... }:
+{ maxRounds ? 3 }:
+{
+  name = "windows-update";
+  compact = true;
+  memSize = 4096;
+  qemuTimeout = 7200;
+  auditScript = ''
+    @echo off
+    setlocal
+
+    :: Track update round via a counter file
+    set "ROUND_FILE=C:\vmix-update-round.txt"
+    set "MAX_ROUNDS=${toString maxRounds}"
+
+    if exist "%ROUND_FILE%" (
+      set /p ROUND=<"%ROUND_FILE%"
+    ) else (
+      set "ROUND=1"
+    )
+
+    echo === vmix: Windows Update round %ROUND% of %MAX_ROUNDS% ===
+
+    :: Ensure Windows Update service is running
+    net start wuauserv 2>nul
+    sc config wuauserv start= auto
+
+    :: Remove any update-blocking policies (LTSC may have these)
+    reg delete "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate" /f 2>nul
+    reg delete "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU" /f 2>nul
+
+    :: Give the service time to initialize on first round
+    if "%ROUND%"=="1" (
+      echo Waiting for Windows Update service to initialize...
+      timeout /t 30 /nobreak >nul
+    )
+
+    :: Run Windows Update via PowerShell COM API
+    powershell -ExecutionPolicy Bypass -Command ^
+      "try {" ^
+      "  $session = New-Object -ComObject Microsoft.Update.Session;" ^
+      "  $searcher = $session.CreateUpdateSearcher();" ^
+      "  Write-Host 'Searching for updates...';" ^
+      "  $result = $searcher.Search('IsInstalled=0');" ^
+      "  $count = $result.Updates.Count;" ^
+      "  Write-Host \"Found $count updates\";" ^
+      "  if ($count -eq 0) { exit 0 };" ^
+      "  foreach ($u in $result.Updates) { Write-Host \" - $($u.Title)\" };" ^
+      "  $updatesToInstall = New-Object -ComObject Microsoft.Update.UpdateColl;" ^
+      "  foreach ($u in $result.Updates) {" ^
+      "    if ($u.EulaAccepted -eq $false) { $u.AcceptEula() };" ^
+      "    $updatesToInstall.Add($u) | Out-Null" ^
+      "  };" ^
+      "  $downloader = $session.CreateUpdateDownloader();" ^
+      "  $downloader.Updates = $updatesToInstall;" ^
+      "  Write-Host 'Downloading...';" ^
+      "  $downloader.Download() | Out-Null;" ^
+      "  $installer = $session.CreateUpdateInstaller();" ^
+      "  $installer.Updates = $updatesToInstall;" ^
+      "  Write-Host 'Installing...';" ^
+      "  $installResult = $installer.Install();" ^
+      "  Write-Host \"Result: $($installResult.ResultCode)\";" ^
+      "  for ($i = 0; $i -lt $updatesToInstall.Count; $i++) {" ^
+      "    $hr = $installResult.GetUpdateResult($i).HResult;" ^
+      "    Write-Host \"  $($updatesToInstall.Item($i).Title): code=$hr\"" ^
+      "  };" ^
+      "  if ($installResult.RebootRequired) { exit 3010 } else { exit 0 }" ^
+      "} catch {" ^
+      "  Write-Host \"ERROR: $_\";" ^
+      "  exit 1" ^
+      "}"
+
+    set "WU_EXIT=%ERRORLEVEL%"
+    echo Windows Update exit code: %WU_EXIT%
+
+    :: Cleanup component store
+    echo Cleaning up component store...
+    dism /Online /Cleanup-Image /StartComponentCleanup /ResetBase /Quiet 2>nul
+
+    :: Check if we need to reboot and continue
+    set /a "NEXT_ROUND=%ROUND%+1"
+
+    if "%WU_EXIT%"=="3010" (
+      if %ROUND% LSS %MAX_ROUNDS% (
+        echo Reboot required, scheduling round %NEXT_ROUND%...
+        echo %NEXT_ROUND% > "%ROUND_FILE%"
+        :: Copy script to a path the wrapper won't delete
+        copy /y "%~f0" "C:\vmix-update-continue.cmd" >nul
+        reg add "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce" /v vmixUpdate /t REG_SZ /d "cmd /c C:\vmix-update-continue.cmd" /f
+        :: Preserve Audit Mode across reboot (updates can reset it)
+        reg add "HKLM\SYSTEM\Setup\Status\AuditBoot" /v AuditBoot /t REG_DWORD /d 1 /f
+        reg add "HKLM\SYSTEM\Setup" /v AuditInProgress /t REG_DWORD /d 1 /f
+        :: Immediate reboot (preempts wrapper shutdown)
+        shutdown /r /f /t 0
+        exit /b
+      ) else (
+        echo Max update rounds reached.
+      )
+    )
+
+    :: Done — clean up and shutdown
+    del /q "%ROUND_FILE%" 2>nul
+    del /q "C:\vmix-update-continue.cmd" 2>nul
+    echo === vmix: Windows Update complete ===
+    shutdown /s /f /t 10 /c "vmix: windows-update complete"
+  '';
+}