Fix devtoprod validateBuild exit-code handling

Ensure Invoke-Npm returns correct exit code without breaking step logic.

Co-authored-by: Cursor <cursoragent@cursor.com>

infra/scripts/deploy-dev-to-prod.ps1

@@ -50,12 +50,26 @@ function Get-StepEnabled {
 
 function Invoke-Npm {
     param([string]$Script, [string[]]$ExtraArgs = @())
-    $args = @('run', $Script)
+    $npmArgs = @('run', $Script)
     if ($ExtraArgs.Count -gt 0) {
-        $args += '--'
+        $npmArgs += '--'
-        $args += $ExtraArgs
+        $npmArgs += $ExtraArgs
+    }
+    # Important: callers assign the return value of this function to a variable
+    # (e.g. `$code = Invoke-Npm 'prod:build'`).
+    # If npm output is sent to the pipeline, PowerShell can accidentally capture
+    # stdout/stderr along with the function return value, breaking exit-code logic.
+    # So we stream npm output to $null and return only the exit code.
+    Write-Host ("Running npm: npm " + ($npmArgs -join ' ')) -ForegroundColor DarkGray
+    # Capture stdout/stderr so the function does not emit pipeline output.
+    $prevEap = $ErrorActionPreference
+    $ErrorActionPreference = 'Continue'
+    $npmOutput = & npm @npmArgs 2>&1
+    $ErrorActionPreference = $prevEap
+
+    foreach ($line in $npmOutput) {
+        Write-Host $line
     }
-    & npm @args
     return $LASTEXITCODE
 }
 
@@ -245,6 +259,7 @@ Write-Host ('Steps: ' + ($enabled -join ', '))
 if (Get-StepEnabled $steps 'validateBuild') {
     $ok = Invoke-Step 'validateBuild' {
         $code = Invoke-Npm 'prod:build'
+        Write-Host ("prod:build exit code: " + $code)
         if ($code -ne 0) { return $code }
 
         # Always prefer the dev host on LAN (192.168.10.70) because the HTTPS dev domain