feat: lit/content-create with Divi short form

New input divi (1-30 sections, short form like lit-divi-insert) builds a Divi 5
layout in one divi/placeholder. The whole description is checked before the
insert (Divi's map for "no entry yet"); the draft is inserted with its normal
WordPress fields only, then DiviContentComposer composes again bound to the new
entry and stores it via DiviSaver::saveNew (same kses window as save(), strict
DiviFlags). A refusal or failure deletes the draft. Result adds tree_rev and the
outline.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Integrations/Divi/Pages/DiviSaver.php

@@ -36,7 +36,8 @@ use WP_Post;
  * transition_post_status, wp_after_insert_post and third-party listeners. No MCP input reaches
  * those hooks except the content itself (already cleaned); anything a third-party hook writes
  * there is saved without kses, as it would be for an administrator. The rollback write in
- * restore() uses the same window with the previous stored content.
+ * restore() uses the same window with the previous stored content; saveNew() (the first layout
+ * of a new draft, lit/content-create) uses it for its single wp_update_post().
  *
  * Divi's own save filters are NOT kses and are never removed (ruling S7, defense in depth):
  * Security::initialize() (Divi 5.2.1 Security.php:74-81) registers on wp_insert_post_data
@@ -116,6 +117,34 @@ class DiviSaver
         return ['revision_id' => $revisionId, 'warnings' => $warnings];
     }
 
+    /**
+     * The first content of a brand-new draft (lit/content-create with divi, which inserted the
+     * draft with its normal WordPress fields – title and excerpt went through kses as usual).
+     * Same kses window as save(), holding only this wp_update_post() and its hooks; no restore
+     * point (the draft has no earlier state) and no static CSS to clear. The Divi flags are part
+     * of the write here: without them the new entry is no Divi layout. Every failure throws –
+     * the caller deletes the draft (all or nothing).
+     *
+     * @return list<string> Warnings (CHANGED_ON_SAVE).
+     * @throws RuntimeException
+     */
+    public function saveNew(int $postId, string $content): array
+    {
+        $result = $this->withoutKses(
+            static fn (): int|WP_Error => wp_update_post(wp_slash(['ID' => $postId, 'post_content' => $content]), true)
+        );
+        if ($result instanceof WP_Error || $result === 0) {
+            $message = $result instanceof WP_Error ? $result->get_error_message() : 'returned 0';
+            throw new RuntimeException(sprintf('wp_update_post(%d) refused the Divi layout: %s', $postId, $message));
+        }
+
+        DiviFlags::set($postId);
+
+        $stored = get_post($postId);
+
+        return $stored instanceof WP_Post && (string) $stored->post_content !== $content ? [self::CHANGED_ON_SAVE] : [];
+    }
+
     /**
      * Runs $write with kses' filters off for users without unfiltered_html (D7); restored in
      * finally, right when $write returns or throws.