Fix TrustedInstaller-owned registry key write via token privileges

- 03-system-registry.ps1: replace .NET OpenSubKey approach with proper
  P/Invoke that enables SeTakeOwnershipPrivilege and SeRestorePrivilege
  before attempting to take ownership of TrustedInstaller-owned keys
  (e.g. HKLM\...\Communications\ConfigureChatAutoInstall)
- Remove SYSTEM scheduled task fallback (not needed with token approach)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/03-system-registry.ps1

@@ -11,11 +11,41 @@ function Write-Log {
     Add-Content -Path $LogFile -Value $line -Encoding UTF8
 }
 
+Add-Type -TypeDefinition @"
+using System;
+using System.Runtime.InteropServices;
+public class RegPrivilege {
+    [DllImport("advapi32.dll", ExactSpelling=true, SetLastError=true)]
+    static extern bool AdjustTokenPrivileges(IntPtr htok, bool disAll, ref TokPriv1Luid newState, int len, IntPtr prev, IntPtr relen);
+    [DllImport("kernel32.dll", ExactSpelling=true)]
+    static extern IntPtr GetCurrentProcess();
+    [DllImport("advapi32.dll", ExactSpelling=true, SetLastError=true)]
+    static extern bool OpenProcessToken(IntPtr h, int acc, ref IntPtr phtok);
+    [DllImport("advapi32.dll", SetLastError=true)]
+    static extern bool LookupPrivilegeValue(string host, string name, ref long pluid);
+    [StructLayout(LayoutKind.Sequential, Pack=1)]
+    struct TokPriv1Luid { public int Count; public long Luid; public int Attr; }
+    const int TOKEN_QUERY = 0x8;
+    const int TOKEN_ADJUST = 0x20;
+    const int SE_PRIVILEGE_ENABLED = 2;
+    public static bool Enable(string privilege) {
+        IntPtr htok = IntPtr.Zero;
+        if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST | TOKEN_QUERY, ref htok)) return false;
+        TokPriv1Luid tp; tp.Count = 1; tp.Luid = 0; tp.Attr = SE_PRIVILEGE_ENABLED;
+        if (!LookupPrivilegeValue(null, privilege, ref tp.Luid)) return false;
+        return AdjustTokenPrivileges(htok, false, ref tp, 0, IntPtr.Zero, IntPtr.Zero);
+    }
+}
+"@ -ErrorAction SilentlyContinue
+
 function Grant-RegWriteAccess {
     param([string]$Path)
-    # Grants Administrators FullControl on a registry key that has restricted ACL.
+    # Grants Administrators FullControl on a TrustedInstaller-owned registry key.
-    # Required for keys owned by TrustedInstaller or with locked-down ACL.
+    # Enables SeTakeOwnershipPrivilege + SeRestorePrivilege to override ACL.
     try {
+        [RegPrivilege]::Enable("SeTakeOwnershipPrivilege") | Out-Null
+        [RegPrivilege]::Enable("SeRestorePrivilege")       | Out-Null
+
         $hive    = $Path -replace '^(HKLM|HKCU|HKU|HKCR|HKCC):\\.*', '$1'
         $subkey  = $Path -replace '^(HKLM|HKCU|HKU|HKCR|HKCC):\\', ''
         $rootKey = switch ($hive) {
@@ -23,17 +53,22 @@ function Grant-RegWriteAccess {
             "HKCU" { [Microsoft.Win32.Registry]::CurrentUser }
             "HKCR" { [Microsoft.Win32.Registry]::ClassesRoot }
         }
-        $rights  = [Microsoft.Win32.RegistryKeyPermissionCheck]::ReadWriteSubTree
+
-        $regRights = [System.Security.AccessControl.RegistryRights]::TakeOwnership
+        # Take ownership (requires SeTakeOwnershipPrivilege)
-        $key = $rootKey.OpenSubKey($subkey, $rights, $regRights)
+        $key = $rootKey.OpenSubKey($subkey,
+            [Microsoft.Win32.RegistryKeyPermissionCheck]::ReadWriteSubTree,
+            [System.Security.AccessControl.RegistryRights]::TakeOwnership)
         if ($key) {
             $acl = $key.GetAccessControl([System.Security.AccessControl.AccessControlSections]::None)
             $acl.SetOwner([System.Security.Principal.NTAccount]"BUILTIN\Administrators")
             $key.SetAccessControl($acl)
             $key.Close()
         }
-        # Re-open with ChangePermissions to grant full control
+
-        $key = $rootKey.OpenSubKey($subkey, $rights, [System.Security.AccessControl.RegistryRights]::ChangePermissions)
+        # Grant FullControl to Administrators (requires ChangePermissions)
+        $key = $rootKey.OpenSubKey($subkey,
+            [Microsoft.Win32.RegistryKeyPermissionCheck]::ReadWriteSubTree,
+            [System.Security.AccessControl.RegistryRights]::ChangePermissions)
         if ($key) {
             $acl  = $key.GetAccessControl()
             $rule = New-Object System.Security.AccessControl.RegistryAccessRule(
@@ -41,12 +76,12 @@ function Grant-RegWriteAccess {
                 [System.Security.AccessControl.RegistryRights]::FullControl,
                 [System.Security.AccessControl.InheritanceFlags]"ContainerInherit,ObjectInherit",
                 [System.Security.AccessControl.PropagationFlags]::None,
-                [System.Security.AccessControl.AccessControlType]::Allow
+                [System.Security.AccessControl.AccessControlType]::Allow)
-            )
             $acl.SetAccessRule($rule)
             $key.SetAccessControl($acl)
             $key.Close()
         }
+        Write-Log "  ACL fixed for $Path" -Level INFO
     }
     catch {
         Write-Log "  Grant-RegWriteAccess failed for $Path - $_" -Level WARN