feat: lit/divi-insert and lit/divi-update

All-or-nothing at ability level (S39), duplicate ids refused (S14),
set and attrs on the same path refused (S38), invalid_attr_path error.

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

src/Abilities/Errors.php

@@ -101,6 +101,24 @@ final class Errors
         return self::make('unsupported', $message, $hint, 400);
     }
 
+    /**
+     * Unknown Divi attribute paths (spec §5.4, §8.2). $fields names every problem of the call,
+     * the unknown paths with their closest known ones.
+     *
+     * @param array<string, string> $fields Input path => problem.
+     */
+    public static function invalidAttrPath(array $fields): WP_Error
+    {
+        return self::make(
+            'invalid_attr_path',
+            'Unbekannte Attributpfade; nichts wurde gespeichert.',
+            'Vorschläge unter fields prüfen; alle gültigen Pfade eines Moduls liefert lit/divi-catalog '
+                . '(direkt: lit-divi-catalog) mit module.',
+            400,
+            ['fields' => $fields]
+        );
+    }
+
     /**
      * A write failed and was rolled back completely.
      *