display kiosk watchdog: relaunch Edge when it goes away
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@@ -287,6 +287,201 @@ Write-Host "display-type '$displayType' -> kiosk Startup shortcut for $kioskUrl"
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"""
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WATCHDOG_FILENAME = 'Register-KioskWatchdog.ps1'
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# Where the watchdog stages the script the scheduled task actually runs. The
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# task must run in the INTERACTIVE session, so its action cannot be an inline
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# payload executed by the SYSTEM enforce task.
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WATCHDOG_TASKNAME = 'ShopDB Kiosk Watchdog'
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WATCHDOG_SCRIPTPATH = r'C:\ProgramData\ShopDB\Watch-ShopdbKiosk.ps1'
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WATCHDOG_INTERVAL_MIN = 2
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def build_watchdog_script():
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"""Return the inline watchdog-installer PowerShell as text.
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WHY THIS EXISTS: the kiosk is launched by an all-users Startup shortcut,
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which runs ONCE at logon. Nothing supervises the browser afterwards, so when
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Edge exits - an update, a crash, someone closing the window - the display
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stays dead until the next logon or reboot.
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The Edge RelaunchNotification=2 policy was intended to cover the update
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case, but it does not: that policy drives Edge's own update-restart flow,
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which depends on session restore to come back to where it was. Kiosk mode
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(--kiosk) restores no session and shows no notification UI, so Edge honours
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the close and never the relaunch.
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This entry runs as SYSTEM under the enforce task and cannot launch a visible
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browser itself (session 0 has no desktop - the same reason the dispatcher
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writes a Startup shortcut). So it REGISTERS a scheduled task that runs in
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the interactive user's session and relaunches the kiosk when it is gone.
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Idempotent: the staged script and the task are rewritten only when they
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differ from what is wanted, so a steady-state cycle costs one file read.
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"""
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# The script the task runs. Kept as a separate literal so the outer f-string
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# does not have to escape its braces.
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watched = r'''# Watch-ShopdbKiosk.ps1 -- relaunch the kiosk browser if it has gone.
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#
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# Runs in the INTERACTIVE user session (see the watchdog task), every couple of
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# minutes. Reads the same Startup shortcut the dispatcher writes, so the target
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# URL has exactly one source of truth: retarget a display by editing the
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# dispatcher, and this follows without change.
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$ErrorActionPreference = 'Continue'
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$logDir = 'C:\Logs\ShopDB'
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$logFile = Join-Path $logDir 'kiosk-watchdog.log'
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$stamp = Join-Path $env:TEMP 'shopdb-kiosk-lastlaunch.txt'
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if (-not (Test-Path $logDir)) {
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New-Item -ItemType Directory -Path $logDir -Force -EA SilentlyContinue | Out-Null
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}
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function Log {
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param([string]$Message)
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# Bounded: this runs every couple of minutes forever on a PC nobody logs
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# into, so an unbounded log would be the only thing that ever fills the disk.
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try {
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if ((Test-Path $logFile) -and ((Get-Item $logFile).Length -gt 512KB)) {
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$keep = Get-Content $logFile -Tail 200 -EA SilentlyContinue
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Set-Content -Path $logFile -Value $keep -EA SilentlyContinue
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}
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} catch { }
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Add-Content -Path $logFile -EA SilentlyContinue `
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-Value ('[{0}] {1}' -f (Get-Date -Format 'yyyy-MM-dd HH:mm:ss'), $Message)
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}
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# The kiosk shortcut is the source of truth for target + arguments.
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$startup = Join-Path $env:ProgramData 'Microsoft\Windows\Start Menu\Programs\StartUp'
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$lnkPath = Join-Path $startup 'ShopDB Kiosk.lnk'
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if (-not (Test-Path -LiteralPath $lnkPath)) {
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# Not a kiosk display, or the dispatcher has not run yet. Do NOT invent a
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# browser launch here - that would put Edge on a PC that never asked for it.
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return
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}
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try {
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$shell = New-Object -ComObject WScript.Shell
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$lnk = $shell.CreateShortcut($lnkPath)
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$target = $lnk.TargetPath
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$arguments = $lnk.Arguments
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} catch {
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Log "could not read $lnkPath : $_"
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return
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}
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if (-not $target -or -not (Test-Path -LiteralPath $target)) {
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Log "shortcut target missing: $target"
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return
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}
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# Match on the COMMAND LINE, not just the image name. Edge spawns a crowd of
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# msedge.exe children (renderers, GPU, crashpad) that outlive nothing useful;
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# testing for "is msedge running" would leave a stray child masking a dead
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# kiosk forever.
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$running = $false
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try {
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$running = [bool](Get-CimInstance Win32_Process -Filter "Name = 'msedge.exe'" -EA SilentlyContinue |
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Where-Object { $_.CommandLine -match '--kiosk' })
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} catch {
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Log "process query failed, assuming kiosk is up: $_"
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return
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}
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if ($running) { return }
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# Debounce. Edge takes a few seconds to present a --kiosk process, and a display
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# that fails to start would otherwise get a new browser every couple of minutes.
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try {
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if (Test-Path $stamp) {
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$last = Get-Content $stamp -First 1 -EA SilentlyContinue
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if ($last) {
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$age = ((Get-Date) - [datetime]$last).TotalSeconds
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if ($age -lt 120) {
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Log ('kiosk still absent {0:N0}s after a launch - not relaunching yet' -f $age)
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return
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}
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}
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}
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} catch { }
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Log "kiosk browser not running - relaunching: $target $arguments"
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try {
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Set-Content -Path $stamp -Value (Get-Date -Format 'o') -EA SilentlyContinue
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Start-Process -FilePath $target -ArgumentList $arguments -EA Stop
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Log 'relaunched.'
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} catch {
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Log "relaunch FAILED: $_"
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}
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'''
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return f"""# Register-KioskWatchdog.ps1 -- gea-shopfloor-display kiosk watchdog.
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#
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# Installs a scheduled task that relaunches the kiosk browser when it is gone.
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# See the manifest comment for why the Startup shortcut alone is not enough.
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#
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# Runs as SYSTEM under the enforce task, so it registers the task rather than
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# launching anything: SYSTEM has no interactive desktop.
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$ErrorActionPreference = 'Continue'
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$taskName = '{WATCHDOG_TASKNAME}'
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$scriptPath = '{WATCHDOG_SCRIPTPATH}'
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$intervalMin = {WATCHDOG_INTERVAL_MIN}
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$wanted = @'
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{watched}
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'@
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# --- stage the script the task runs --------------------------------------
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$dir = Split-Path -Parent $scriptPath
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if (-not (Test-Path $dir)) {{ New-Item -ItemType Directory -Path $dir -Force | Out-Null }}
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$current = ''
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if (Test-Path -LiteralPath $scriptPath) {{
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$current = Get-Content -LiteralPath $scriptPath -Raw -EA SilentlyContinue
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}}
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# Compare trimmed: Set-Content appends a trailing newline that the here-string
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# does not carry, so a raw comparison never matches and the file is rewritten
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# every enforce cycle forever.
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if ($current.TrimEnd() -ne $wanted.TrimEnd()) {{
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Set-Content -LiteralPath $scriptPath -Value $wanted -Encoding UTF8 -Force
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Write-Host "staged $scriptPath"
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}} else {{
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Write-Host "watchdog script already current"
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}}
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# --- register the task ----------------------------------------------------
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# Principal is the INTERACTIVE users group, not SYSTEM: the relaunched browser
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# has to appear on the auto-login user's visible desktop. A SYSTEM task would
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# start Edge in session 0 where nobody can see it.
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$existing = Get-ScheduledTask -TaskName $taskName -EA SilentlyContinue
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if (-not $existing) {{
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try {{
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$action = New-ScheduledTaskAction -Execute 'powershell.exe' `
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-Argument ('-NoProfile -WindowStyle Hidden -ExecutionPolicy Bypass -File "{{0}}"' -f $scriptPath)
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$atLogon = New-ScheduledTaskTrigger -AtLogOn
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# -Once + -RepetitionInterval repeats indefinitely. Do NOT pass
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# -RepetitionDuration [TimeSpan]::MaxValue: it serialises to an
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# out-of-range Duration that Register-ScheduledTask rejects.
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$repeat = New-ScheduledTaskTrigger -Once -At ((Get-Date).AddMinutes(1)) `
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-RepetitionInterval (New-TimeSpan -Minutes $intervalMin)
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$principal = New-ScheduledTaskPrincipal -GroupId 'S-1-5-32-545' -RunLevel Limited
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$settings = New-ScheduledTaskSettingsSet -StartWhenAvailable `
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-MultipleInstances IgnoreNew -ExecutionTimeLimit (New-TimeSpan -Minutes 5) `
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-DontStopIfGoingOnBatteries -AllowStartIfOnBatteries
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Register-ScheduledTask -TaskName $taskName -Action $action `
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-Trigger @($atLogon, $repeat) -Principal $principal -Settings $settings `
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-Force | Out-Null
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Write-Host "registered '$taskName' (every $intervalMin min, interactive)"
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}} catch {{
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Write-Host "FAILED to register '$taskName': $_"
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}}
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}} else {{
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Write-Host "'$taskName' already registered"
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}}
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"""
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ALWAYSON_FILENAME = 'Set-DisplayAlwaysOn.ps1'
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@@ -416,6 +611,26 @@ def build_display_manifest():
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'PayloadRef': DISPATCHER_FILENAME,
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'DetectionMethod': 'Always',
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},
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{
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'_comment': (
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'Relaunch the kiosk browser when it goes away. The Startup '
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'shortcut the dispatcher writes runs ONCE at logon, so an Edge '
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'update, a crash or a closed window leaves the display dead '
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'until the next logon. RelaunchNotification=2 does not cover '
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'it: that policy drives Edge\'s update-restart, which relies on '
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'session restore, and --kiosk restores no session and shows no '
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'notification UI. Registers an INTERACTIVE-session scheduled '
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'task (SYSTEM cannot launch a visible browser) that relaunches '
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'from the same shortcut every '
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f'{WATCHDOG_INTERVAL_MIN} minutes when no --kiosk process is '
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'running.'),
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'Name': 'Display kiosk watchdog (relaunch Edge)',
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'Type': 'PS1',
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'Script': WATCHDOG_FILENAME,
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'PayloadSource': 'inline',
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'PayloadRef': WATCHDOG_FILENAME,
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'DetectionMethod': 'Always',
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},
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{
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'_comment': (
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'Keep the display awake 24/7 so the kiosk page stays visible: '
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@@ -472,6 +687,13 @@ def seed_display_scope(publish=False, notes='seed gea-shopfloor-display'):
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alwayson, ALWAYSON_FILENAME,
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'text/plain; charset=utf-8', alwaysonbytes)
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watchdog = next(entry for entry in scope.entries
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if entry.name == 'Display kiosk watchdog (relaunch Edge)')
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watchdogbytes = build_watchdog_script().encode('utf-8')
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watchdogpayload = service.store_inline_payload(
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watchdog, WATCHDOG_FILENAME,
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'text/plain; charset=utf-8', watchdogbytes)
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publishedversion = None
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if publish:
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publishedversion = service.publish_scope(
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@@ -485,5 +707,6 @@ def seed_display_scope(publish=False, notes='seed gea-shopfloor-display'):
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'entrytypes': [entry.entrytype for entry in scope.entries],
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'dispatchersha256': payload.payloadsha256,
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'alwaysonsha256': alwaysonpayload.payloadsha256,
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'watchdogsha256': watchdogpayload.payloadsha256,
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'publishedversion': publishedversion,
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}
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