generalize: keep the static address from stranding the box after a reboot

It worked on the first boot and was gone after a later internal reboot -- no
IPv4 at all, not even DHCP. DHCP is turned off before the address is set, so
anything that stops the set mid-way leaves the interface with nothing. A stale
ARP entry for the address, left on the network by the previous instance,
tripped duplicate-address detection and made New-NetIPAddress throw; with
-ErrorAction Stop that aborted the script with DHCP already off.

DadTransmits 0 turns that detection off so the static binds regardless of what
the network remembers, and the assignment is now retried a few times rather
than fatal on the first throw. Moved to its own .ps1 -- a wait loop and a retry
are not worth keeping correct inside a cmd one-liner.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0117qMyjpuXsjpVAcpJbFD8g

lib/images/windows/templates/generalize.nix

@@ -93,12 +93,48 @@ in
   # interface arrives DHCP-managed -- assigning an address without turning DHCP
   # off first does not stick, which is how a VM meant to be at a fixed address
   # ended up holding a lease instead.
+  # PowerShell in its own file: it grew a wait loop and a retry, which are no
+  # fun to keep correct inside a cmd one-liner.
+  #
+  # Two things it must survive. DHCP is turned off before the address is set,
+  # so any failure to set it strands the box with no address at all -- which is
+  # exactly what happened after an internal reboot, where a stale ARP entry for
+  # the address from the previous instance tripped duplicate-address detection
+  # and New-NetIPAddress threw. DadTransmits 0 turns that detection off so the
+  # static always binds, and the assignment is retried rather than fatal.
+  staticIPScriptPs1 = pkgs.writeText "vmix-static-ip.ps1" ''
+    $a = $null
+    for ($n = 0; $n -lt 30; $n++) {
+      $a = Get-NetAdapter -Physical | Where-Object Status -eq 'Up' | Sort-Object ifIndex | Select-Object -First 1
+      if ($a) { break }
+      Start-Sleep -Seconds 2
+    }
+    if (-not $a) { Write-Output 'vmix: no adapter came up'; exit 1 }
+    $i = $a.ifIndex
+    Set-NetIPInterface -InterfaceIndex $i -Dhcp Disabled -DadTransmits 0 -ErrorAction SilentlyContinue
+    Remove-NetIPAddress -InterfaceIndex $i -AddressFamily IPv4 -Confirm:$false -ErrorAction SilentlyContinue
+    Remove-NetRoute -InterfaceIndex $i -AddressFamily IPv4 -Confirm:$false -ErrorAction SilentlyContinue
+    $ok = $false
+    for ($k = 0; $k -lt 5 -and -not $ok; $k++) {
+      try {
+        New-NetIPAddress -InterfaceIndex $i -IPAddress '${staticIP.address}' -PrefixLength ${toString staticIP.prefixLength} -DefaultGateway '${staticIP.gateway}' -ErrorAction Stop | Out-Null
+        $ok = $true
+      } catch {
+        Write-Output ('vmix: assign attempt ' + $k + ' failed: ' + $_.Exception.Message)
+        Start-Sleep -Seconds 2
+        Remove-NetIPAddress -InterfaceIndex $i -AddressFamily IPv4 -Confirm:$false -ErrorAction SilentlyContinue
+      }
+    }
+    if (-not $ok) { Write-Output 'vmix: could not set static address'; exit 1 }
+    Set-DnsClientServerAddress -InterfaceIndex $i -ServerAddresses ${staticDnsList}
+    New-NetFirewallRule -DisplayName 'ICMPv4 Echo' -Protocol ICMPv4 -IcmpType 8 -Direction Inbound -Action Allow -Profile Any -Enabled True -ErrorAction SilentlyContinue | Out-Null
+    Write-Output ('vmix: set ${staticIP.address} on ifIndex ' + $i)
+  '';
+
+  # Thin launcher, so the scheduled task has a cmd to point at.
   staticIPScript = pkgs.writeText "vmix-static-ip.cmd" ''
     @echo off
-    powershell -NoProfile -ExecutionPolicy Bypass -Command "$a = $null; for ($n = 0; $n -lt 30; $n++) { $a = Get-NetAdapter -Physical | Where-Object Status -eq 'Up' | Sort-Object ifIndex | Select-Object -First 1; if ($a) { break }; Start-Sleep -Seconds 2 }; if (-not $a) { Write-Output 'vmix: no adapter came up'; exit 1 }; $i = $a.ifIndex; Set-NetIPInterface -InterfaceIndex $i -Dhcp Disabled -ErrorAction SilentlyContinue; Remove-NetIPAddress -InterfaceIndex $i -AddressFamily IPv4 -Confirm:$false -ErrorAction SilentlyContinue; Remove-NetRoute -InterfaceIndex $i -AddressFamily IPv4 -Confirm:$false -ErrorAction SilentlyContinue; New-NetIPAddress -InterfaceIndex $i -IPAddress '${staticIP.address}' -PrefixLength ${toString staticIP.prefixLength} -DefaultGateway '${staticIP.gateway}' -ErrorAction Stop | Out-Null; Set-DnsClientServerAddress -InterfaceIndex $i -ServerAddresses ${staticDnsList}; Write-Output ('vmix: set ' + '${staticIP.address}' + ' on ifIndex ' + $i)" > C:\Windows\Temp\vmix-static-ip.log 2>&1
+    powershell -NoProfile -ExecutionPolicy Bypass -File C:\vmix-static-ip.ps1 > C:\Windows\Temp\vmix-static-ip.log 2>&1
-    :: Answer pings. Windows blocks ICMP by default, which makes a box with a
-    :: fixed address look dead to everything that checks it the obvious way.
-    powershell -NoProfile -Command "New-NetFirewallRule -DisplayName 'ICMPv4 Echo' -Protocol ICMPv4 -IcmpType 8 -Direction Inbound -Action Allow -Profile Any -Enabled True | Out-Null" > nul 2>&1
   '';
 
   dataDriveLetter = if dataDisk != null then (dataDisk.driveLetter or "D") else "D";
@@ -413,7 +449,10 @@ in {
       { source = bootDataProfileScript; dest = "/vmix-data-profile.cmd"; }
     ]
     ++ lib.optional (writeFilter != null) { source = uwfConfigScript; dest = "/vmix-uwf-config.cmd"; }
-    ++ lib.optional (staticIP != null) { source = staticIPScript; dest = "/vmix-static-ip.cmd"; };
+    ++ lib.optionals (staticIP != null) [
+      { source = staticIPScript; dest = "/vmix-static-ip.cmd"; }
+      { source = staticIPScriptPs1; dest = "/vmix-static-ip.ps1"; }
+    ];
   # delayOobeRun: sysprep + shutdown — OOBE runs on real hardware
   # generalize: sysprep + reboot into OOBE in the same QEMU session
   auditScript = ''