Fix reboot race + dispatcher owns all reboots

Two related fixes from the pipeline audit:

1. Stage-Dispatcher race condition (critical):
   Run-ShopfloorSetup.ps1 called shutdown /r /t 10 and the dispatcher
   had to write the next stage + register RunOnce within that 10-second
   window. If disk I/O was slow, the reboot fired before RunOnce was
   registered, and the chain broke.

   Fix: dispatcher now cancels Run-ShopfloorSetup's pending reboot
   (shutdown /a) immediately after it returns, then advances the stage
   and registers RunOnce with no time pressure, then initiates its own
   shutdown /r /t 5.

2. Dispatcher owns all reboots:
   Run-ShopfloorSetup.ps1 now checks the -FromDispatcher flag at the
   end. When called by the dispatcher, it schedules shutdown /r /t 30
   as a safety net (the dispatcher cancels it immediately). When called
   standalone (manual run or legacy FirstLogonCommands), it reboots
   directly with /t 10 as before.

   This means the dispatcher has full control over the reboot lifecycle:
   cancel -> advance stage -> register RunOnce -> reboot. No racing.

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

playbook/shopfloor-setup/Run-ShopfloorSetup.ps1

@@ -208,5 +208,14 @@ Write-Host "================================================================"
 # Flush transcript before shutdown so the log file is complete on next boot
 try { Stop-Transcript | Out-Null } catch {}
 
+if ($FromDispatcher) {
+    # Dispatcher owns the reboot — it cancels ours and reboots on its own
+    # terms after advancing the stage and re-registering RunOnce. We still
+    # schedule one as a safety net (dispatcher cancels it immediately).
+    Write-Host "Returning to Stage-Dispatcher for reboot."
+    shutdown /r /t 30
+} else {
+    # Standalone run (manual or legacy FirstLogonCommands) — reboot directly.
     Write-Host "Rebooting in 10 seconds..."
     shutdown /r /t 10
+}

playbook/shopfloor-setup/Stage-Dispatcher.ps1

@@ -86,18 +86,20 @@ switch ($stage) {
             break
         }
 
-        # Run-ShopfloorSetup.ps1 calls shutdown /r /t 10 at the end, which
-        # gives us a ~10 second window after it returns to advance the stage
-        # and re-register RunOnce before the reboot fires.
         # -FromDispatcher bypasses the stage-file gate at the top of
         # Run-ShopfloorSetup (which would otherwise see the stage file
         # and exit immediately thinking it should defer to us).
         & $script -FromDispatcher
 
-        Write-Host "Run-ShopfloorSetup.ps1 finished. Advancing stage to sync-intune."
+        # Cancel whatever reboot Run-ShopfloorSetup scheduled (shutdown /r
+        # /t 10) so we can advance the stage and re-register RunOnce WITHOUT
+        # racing a 10-second fuse. Then reboot on our own terms.
+        Write-Host "Run-ShopfloorSetup.ps1 finished. Canceling its reboot so we can advance safely."
+        cmd /c "shutdown /a 2>nul" *>$null
         Set-Content -LiteralPath $stageFile -Value 'sync-intune' -Force
         Register-NextRun
-        Write-Host "Reboot imminent (initiated by Run-ShopfloorSetup.ps1)."
+        Write-Host "Stage advanced to sync-intune. Rebooting."
+        shutdown /r /t 5
     }
 
     'sync-intune' {