RDoc-4100 Make CloudFront function code an update/publish a build step

scripts/deploy.ps1

@@ -257,8 +257,16 @@ if ($DryRun) {
     Write-Host "Updating CloudFront KeyValueStore" -ForegroundColor Cyan
     Update-CloudFrontKVS
 
+    # A config-sync failure must not strand the content phases 1 and 2 already uploaded, so the
+    # error is held and rethrown after the invalidation and cleanup. The build still goes red.
     Write-Host 'Syncing CloudFront configuration' -ForegroundColor Cyan
-    Sync-CloudFrontConfig
+    $configError = $null
+    try {
+        Sync-CloudFrontConfig
+    } catch {
+        $configError = $_
+        Write-Host "  CloudFront config sync failed: $_" -ForegroundColor Red
+    }
 
     if ($CloudFrontDistributionId) {
         Write-Host "Invalidating CloudFront distribution $CloudFrontDistributionId" -ForegroundColor Cyan
@@ -276,6 +284,8 @@ if ($DryRun) {
         --delete
     if ($LASTEXITCODE) { throw 'aws s3 sync (hashed assets – cleanup) failed' }
 
+    if ($configError) { throw $configError }
+
 }
 
 Write-Host 'Deployment completed successfully.' -ForegroundColor Green

scripts/lib/cloudfront-common.ps1

@@ -35,6 +35,36 @@ function Invoke-CloudFrontInvalidation {
     if ($LASTEXITCODE) { throw 'CloudFront invalidation failed' }
 }
 
+# get-response-headers-policy returns `{}` for headers that are not configured, but
+# update-response-headers-policy refuses them: once XSSProtection, FrameOptions or ReferrerPolicy
+# appears in the payload it requires its own fields. The read shape is therefore not a valid write
+# shape, so empty objects are dropped before the config goes back. Empty arrays are left alone,
+# since {Quantity: 0, Items: []} is valid on the way in.
+function Remove-EmptyObjects {
+    param([AllowNull()] $Node)
+
+    if ($null -eq $Node) { return $null }
+
+    if ($Node -is [System.Collections.IEnumerable] -and $Node -isnot [string]) {
+        $items = [System.Collections.ArrayList]::new()
+        foreach ($item in $Node) { [void]$items.Add((Remove-EmptyObjects $item)) }
+        # Comma-prefix keeps a one-element array an array; returning it bare would unroll it to a
+        # scalar and turn {Items: ["x"]} into {Items: "x"}, which CloudFront rejects.
+        return , $items.ToArray()
+    }
+
+    if ($Node -isnot [System.Management.Automation.PSCustomObject]) { return $Node }
+
+    $kept = [ordered]@{}
+    foreach ($property in $Node.PSObject.Properties) {
+        $value = Remove-EmptyObjects $property.Value
+        $isEmptyObject = $value -is [System.Management.Automation.PSCustomObject] -and
+            @($value.PSObject.Properties).Count -eq 0
+        if (-not $isEmptyObject) { $kept[$property.Name] = $value }
+    }
+    return [pscustomobject]$kept
+}
+
 # Paths where $Candidate differs from $Reference: node kind, array length, added or dropped
 # property, or scalar value. Proves a patch touched only the field it meant to.
 function Get-JsonDifference {

scripts/sync-csp.ps1

@@ -50,7 +50,7 @@ $current = aws cloudfront get-response-headers-policy --id $ResponseHeadersPolic
 if ($LASTEXITCODE) { throw 'aws get-response-headers-policy failed' }
 
 $etag = $current.ETag
-$config = $current.ResponseHeadersPolicy.ResponseHeadersPolicyConfig
+$config = Remove-EmptyObjects $current.ResponseHeadersPolicy.ResponseHeadersPolicyConfig
 
 if (Compare-CloudFrontValue -Live $config.SecurityHeadersConfig.ContentSecurityPolicy.ContentSecurityPolicy -Local $csp -Noun 'policy') { return }
 
@@ -105,7 +105,8 @@ try {
 $reread = aws cloudfront get-response-headers-policy --id $ResponseHeadersPolicyId | ConvertFrom-Json
 if ($LASTEXITCODE) { throw 'aws get-response-headers-policy failed on re-read' }
 
-$now = $reread.ResponseHeadersPolicy.ResponseHeadersPolicyConfig | ConvertTo-Json -Depth 30 -Compress | ConvertFrom-Json
+$now = Remove-EmptyObjects $reread.ResponseHeadersPolicy.ResponseHeadersPolicyConfig |
+    ConvertTo-Json -Depth 30 -Compress | ConvertFrom-Json
 $postDiffs = @(Get-JsonDifference -Reference $before -Candidate $now | Where-Object { $_ -notlike "$CspPath*" })
 if ($postDiffs.Count) {
     throw "The policy changed outside the CSP: $($postDiffs -join '; '). Restore the affected headers from the CloudFront console."