Use marker file instead of task unregister for sync completion

BUILTIN\Users (Limited RunLevel) can't delete scheduled tasks, so
Unregister-ScheduledTask failed silently and the sync task kept firing
at every logon even after completion.

Fix: write C:\Enrollment\sync-complete.txt on completion. At script
startup in -AsTask mode, check for the marker and exit immediately if
found. The task stays in Task Scheduler but does nothing -- fires at
logon, sees marker, exits in under a second. No visible window.

Manual sync_intune.bat runs (no -AsTask) ignore the marker and always
show the full status display for inventory QR code purposes.

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

playbook/shopfloor-setup/Shopfloor/lib/Monitor-IntuneProgress.ps1

@@ -560,11 +560,16 @@ function Invoke-SetupComplete {
     Write-Host "The post-reboot DSC install phase is finished. The device is ready."
 
     if ($AsTask) {
-        # Task mode: unregister our own scheduled task
-        Write-Host "Unregistering sync task..." -ForegroundColor Cyan
+        # Write completion marker so future logon-triggered runs exit
+        # immediately. We can't Unregister-ScheduledTask because the task
+        # runs as BUILTIN\Users (Limited) which lacks permission to delete
+        # tasks. The marker file makes the task a harmless no-op.
         try {
-            Unregister-ScheduledTask -TaskName 'Shopfloor Intune Sync' -Confirm:$false -ErrorAction SilentlyContinue
-        } catch {}
+            Set-Content -LiteralPath $syncCompleteMarker -Value (Get-Date -Format 'o') -Force
+            Write-Host "Sync complete marker written." -ForegroundColor Green
+        } catch {
+            Write-Warning "Failed to write completion marker: $_"
+        }
 
         # Machine number prompt only (startup items are auto-applied by
         # 06-OrganizeDesktop from the PC profile). Tech can re-open
@@ -636,6 +641,17 @@ function Invoke-RebootPrompt {
 # Terminal - neither reliably honors programmatic window resize, so we
 # solve it by controlling cursor position instead.
 # ============================================================================
+$syncCompleteMarker = 'C:\Enrollment\sync-complete.txt'
+
+# If running as a scheduled task and sync already completed on a prior run,
+# exit immediately. The task stays registered (BUILTIN\Users can't delete
+# tasks) but does nothing -- fires at logon, sees marker, exits in <1s.
+if ($AsTask -and (Test-Path -LiteralPath $syncCompleteMarker)) {
+    Write-Host "Sync already complete (marker exists). Exiting."
+    try { Stop-Transcript | Out-Null } catch {}
+    exit 0
+}
+
 try {
     $qrText = Build-QRCodeText
     $qrRefreshed = [bool]($qrText -notmatch 'not yet Azure AD joined')