fix: preserve selections when config import is invalid (#4994)

* fix: validate imports before replacing selections

* test: cover atomic config imports

* docs: explain stale config imports

---------

Co-authored-by: Guilherme de Oliveira Rocha <contatoguilhermeoliveira@protonmail.com>
Co-authored-by: Chris Titus <contact@christitus.com>

functions/private/Update-WinUtilSelections.ps1

@@ -1,4 +1,19 @@
-function Update-WinUtilSelections ($flatJson) {
+function Update-WinUtilSelections {
+    param(
+        [Parameter(Mandatory)]
+        [string[]]$flatJson,
+
+        [switch]$Replace
+    )
+
+    $nextSelections = @{
+        selectedApps     = [System.Collections.Generic.List[string]]::new()
+        selectedTweaks   = [System.Collections.Generic.List[string]]::new()
+        selectedToggles  = [System.Collections.Generic.List[string]]::new()
+        selectedFeatures = [System.Collections.Generic.List[string]]::new()
+        selectedAppx     = [System.Collections.Generic.List[string]]::new()
+    }
+
     foreach ($cbkey in $flatJson) {
 
         $listName = switch -Regex ($cbkey) {
@@ -9,6 +24,45 @@ function Update-WinUtilSelections ($flatJson) {
             '^WPFAppx'    { 'selectedAppx' }
         }
 
-        $sync.$listName.Add($cbkey)
+        if (-not $listName) {
+            throw "Unsupported selection key '$cbkey'."
+        }
+
+        $isKnownSelection = switch ($listName) {
+            'selectedApps' {
+                $sync.configs.applicationsHashtable.ContainsKey($cbkey)
+            }
+            'selectedTweaks' {
+                $null -ne $sync.configs.tweaks.PSObject.Properties[$cbkey]
+            }
+            'selectedToggles' {
+                $null -ne $sync.configs.tweaks.PSObject.Properties[$cbkey]
+            }
+            'selectedFeatures' {
+                $null -ne $sync.configs.feature.PSObject.Properties[$cbkey]
+            }
+            'selectedAppx' {
+                $sync.configs.appxHashtable.ContainsKey($cbkey)
+            }
+        }
+
+        if (-not $isKnownSelection) {
+            throw "Unknown selection key '$cbkey'."
+        }
+
+        $nextSelections[$listName].Add($cbkey)
+    }
+
+    if ($Replace) {
+        foreach ($listName in $nextSelections.Keys) {
+            $sync[$listName] = $nextSelections[$listName]
+        }
+        return
+    }
+
+    foreach ($listName in $nextSelections.Keys) {
+        foreach ($cbkey in $nextSelections[$listName]) {
+            $sync.$listName.Add($cbkey)
+        }
     }
 }