fix: keep menu items in parent cycles, tighten menu write tests

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Integrations/WordPress/Menus/MenuTree.php

@@ -21,20 +21,55 @@ final class MenuTree
     public static function build(array $items): array
     {
         $nodes = [];
+        $parentOf = [];
         foreach ($items as $item) {
-            $nodes[(int) $item->ID] = self::node($item);
+            $id = (int) $item->ID;
+            $nodes[$id] = self::node($item);
+            $parentOf[$id] = (int) $item->menu_item_parent;
         }
 
         $children = [];
-        foreach ($items as $item) {
-            $id = (int) $item->ID;
-            $parent = (int) $item->menu_item_parent;
-            $children[$parent !== $id && isset($nodes[$parent]) ? $parent : 0][] = $id;
+        foreach (array_keys($nodes) as $id) {
+            $children[self::topLevelParent($id, $parentOf, $nodes)][] = $id;
         }
 
         return self::attach(0, $nodes, $children);
     }
 
+    /**
+     * The parent to attach $id under: its own menu_item_parent, unless that would
+     * make $id unreachable from the root – a self-parent, a parent missing from
+     * this menu, or a chain of parents that cycles back on itself instead of
+     * reaching the root (0) within count($nodes) steps (e.g. A's parent is B and
+     * B's parent is A). Any of these fall back to the top level (0): a broken or
+     * cyclic parent link must never make an item disappear from the tree.
+     *
+     * @param array<int, int>                  $parentOf
+     * @param array<int, array<string, mixed>> $nodes
+     */
+    private static function topLevelParent(int $id, array $parentOf, array $nodes): int
+    {
+        $parent = $parentOf[$id];
+        if ($parent === $id || ! isset($nodes[$parent])) {
+            return 0;
+        }
+
+        $current = $parent;
+        for ($steps = 0; $steps < count($nodes); $steps++) {
+            if ($current === 0) {
+                return $parent;
+            }
+
+            if (! isset($nodes[$current])) {
+                return 0;
+            }
+
+            $current = $parentOf[$current];
+        }
+
+        return 0;
+    }
+
     /** @return array{id: int, title: string, type: string, object: string, object_id: int, url: string} */
     public static function node(object $item): array
     {