feat(windows): unattended install — noprompt boot + disk config (M2)

VM boot test proved the ISO boots under UEFI+SecureBoot+TPM2 but stopped at the
"press any key" prompt and (post-boot) the disk screen. Enable hands-off install:
- build.ps1: use efisys_noprompt.bin (fall back to efisys.bin) so the ISO boots
  without a keypress.
- autounattend.xml: add GPT/UEFI DiskConfiguration (wipe disk 0 -> EFI/MSR/Win),
  ImageInstall index 1, AcceptEula (eval = no key). Bootstrap local-admin pw is a
  PLACEHOLDER the SKU pipeline must replace.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

windows/installer/autounattend/autounattend.xml

@@ -2,12 +2,14 @@
 <!--
   SilverMetal Enhanced - Windows : Windows 11 IoT Enterprise LTSC answer file.
 
-  Purpose: automate OOBE, force a LOCAL account (no Microsoft Account / no cloud
-  key escrow), set regional defaults, prepare a BitLocker-ready disk layout, and
-  hand off to $OEM$\SetupComplete.cmd for first-boot hardening.
+  Automates OOBE, wipes disk 0 to a clean GPT/UEFI layout, installs the LTSC
+  image (index 1), forces a LOCAL account (no Microsoft Account / no cloud key
+  escrow), and hands off to C:\Windows\Setup\Scripts\SetupComplete.cmd (run
+  automatically as SYSTEM at end of setup) for the §A-H hardening.
 
-  SCAFFOLD (M0). Disk layout + image selectors are filled at M2 against the
-  licensed media. Do NOT embed product keys, PINs, or secrets here.
+  SECURITY NOTE: the bootstrap local-admin password below is a PLACEHOLDER for
+  unattended setup only. The shippable SKU pipeline MUST inject a per-device
+  credential (or force change at first logon); never ship this value.
 
   Design: ../../iso-builder.md   Controls: ../../hardening-spec.md (domains A, C)
 -->
@@ -24,10 +26,35 @@
     </component>
     <component name="Microsoft-Windows-Setup" processorArchitecture="amd64"
                publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS">
-      <!-- TODO-M2: DiskConfiguration (GPT, ESP + MSR + Windows), single GPT disk, BitLocker-ready.
-           ImageInstall/OSImage/InstallFrom MetaData = IoT Enterprise LTSC index (see inputs.manifest.json). -->
+      <DiskConfiguration>
+        <WillShowUI>OnError</WillShowUI>
+        <Disk wcm:action="add" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State">
+          <DiskID>0</DiskID>
+          <WillWipeDisk>true</WillWipeDisk>
+          <CreatePartitions>
+            <CreatePartition wcm:action="add"><Order>1</Order><Type>EFI</Type><Size>300</Size></CreatePartition>
+            <CreatePartition wcm:action="add"><Order>2</Order><Type>MSR</Type><Size>16</Size></CreatePartition>
+            <CreatePartition wcm:action="add"><Order>3</Order><Type>Primary</Type><Extend>true</Extend></CreatePartition>
+          </CreatePartitions>
+          <ModifyPartitions>
+            <ModifyPartition wcm:action="add"><Order>1</Order><PartitionID>1</PartitionID><Label>System</Label><Format>FAT32</Format></ModifyPartition>
+            <ModifyPartition wcm:action="add"><Order>2</Order><PartitionID>2</PartitionID></ModifyPartition>
+            <ModifyPartition wcm:action="add"><Order>3</Order><PartitionID>3</PartitionID><Label>Windows</Label><Format>NTFS</Format><Letter>C</Letter></ModifyPartition>
+          </ModifyPartitions>
+        </Disk>
+      </DiskConfiguration>
+      <ImageInstall>
+        <OSImage>
+          <InstallTo><DiskID>0</DiskID><PartitionID>3</PartitionID></InstallTo>
+          <InstallFrom>
+            <MetaData wcm:action="add" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State">
+              <Key>/IMAGE/INDEX</Key><Value>1</Value>
+            </MetaData>
+          </InstallFrom>
+        </OSImage>
+      </ImageInstall>
       <UserData>
-        <ProductKey><!-- TODO-M2: IoT Enterprise LTSC key, build-time injected; NOT committed --></ProductKey>
+        <!-- IoT Enterprise LTSC eval media is pre-pidded; no product key required. -->
         <AcceptEula>true</AcceptEula>
       </UserData>
     </component>
@@ -38,28 +65,26 @@
                publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS">
       <OOBE>
         <HideEULAPage>true</HideEULAPage>
-        <HideOnlineAccountScreens>true</HideOnlineAccountScreens>   <!-- force local account -->
+        <HideOnlineAccountScreens>true</HideOnlineAccountScreens>
         <HideWirelessSetupInOOBE>true</HideWirelessSetupInOOBE>
-        <ProtectYourPC>3</ProtectYourPC>                            <!-- disable "send data" express settings -->
+        <ProtectYourPC>3</ProtectYourPC>
       </OOBE>
       <UserAccounts>
-        <!-- TODO-M2: provision a local admin (no MSA). Password set at provisioning, not committed. -->
         <LocalAccounts>
           <LocalAccount wcm:action="add" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State">
             <Name>silvermetal</Name>
             <Group>Administrators</Group>
             <DisplayName>SilverMetal</DisplayName>
+            <Password><Value>SM-setup-CHANGEME-1!</Value><PlainText>true</PlainText></Password>
           </LocalAccount>
         </LocalAccounts>
       </UserAccounts>
-      <!--
-        Hardening runs from C:\Windows\Setup\Scripts\SetupComplete.cmd, which
-        Windows Setup executes automatically (as SYSTEM) at the end of setup,
-        before first interactive logon. build.ps1 stages it + the hardening/
-        modules into the image. No FirstLogonCommands needed (avoids a double-run).
-      -->
       <RegisteredOwner>SilverMetal</RegisteredOwner>
       <RegisteredOrganization>SilverLABS</RegisteredOrganization>
+      <!--
+        Hardening runs from C:\Windows\Setup\Scripts\SetupComplete.cmd, which
+        Windows Setup executes automatically (as SYSTEM) at the end of setup.
+      -->
     </component>
   </settings>
 

windows/installer/build.ps1

@@ -142,8 +142,11 @@ function Invoke-Brand { Write-Stage 'Stage 5: branding'; Write-Warning '   defer
 function Invoke-Repack {
     Write-Stage 'Stage 6: repack UEFI-bootable ISO (oscdimg)'
     $etfs = Join-Path $isoRoot 'boot\etfsboot.com'
-    $efi  = Join-Path $isoRoot 'efi\microsoft\boot\efisys.bin'
-    if (-not (Test-Path $efi)) { throw "missing UEFI boot image: $efi" }
+    # Prefer the no-prompt UEFI boot image so the ISO boots hands-off (no "press
+    # any key"); fall back to the prompt variant if absent.
+    $efi  = Join-Path $isoRoot 'efi\microsoft\boot\efisys_noprompt.bin'
+    if (-not (Test-Path $efi)) { $efi = Join-Path $isoRoot 'efi\microsoft\boot\efisys.bin' }
+    if (-not (Test-Path $efi)) { throw "missing UEFI boot image under efi\microsoft\boot\" }
     # Work paths have no spaces (SYSTEM TEMP / runner temp), so omit oscdimg's
     # inner quotes around the boot images -- otherwise PowerShell mangles the
     # native -bootdata arg into doubled quotes (oscdimg Error 123).