feat: lit/library-save creates library entries like Divi (E4)

Reuses NewDraft for insert and rollback (P6), requires edit_global_library
for scope global (P7), refuses opaque and global roots before wrapping (P11)
and checks the node with StoredNodeGuard. The source page is never written.

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

src/Integrations/WordPress/Content/NewDraft.php

@@ -22,7 +22,8 @@ defined('ABSPATH') || exit;
  *   returned like any invalid input; partial write if the delete fails.
  * - discard(): writing after the insert failed – created terms and the draft are deleted;
  *   rolled back, or partial write if that cleanup failed.
- * Partial writes are logged with result "partial".
+ * Partial writes are logged with result "partial". lit/library-save reuses it for a new library
+ * entry (ruling P6): no PostWriter (no terms of its own to clean up), $noun names the entry.
  */
 final class NewDraft
 {
@@ -30,11 +31,13 @@ final class NewDraft
     public const REASON_EXTRAS = 'Felder, Begriffe oder Beitragsbild konnten nicht gespeichert werden.';
     public const REASON_LAYOUT = 'Das Divi-Layout konnte nicht gespeichert werden.';
 
+    /** @param string $noun What the new post is called in change-log summaries. */
     public function __construct(
-        private PostWriter $writer,
+        private ?PostWriter $writer,
         private ChangeLog $log,
         private string $ability,
-        private string $postType
+        private string $postType,
+        private string $noun = 'Entwurf'
     ) {
     }
 
@@ -50,7 +53,7 @@ final class NewDraft
         } catch (Throwable $e) {
             // A hook threw – the row may or may not exist and its ID is unknown; nothing is
             // searched or deleted, the client is told to check (lit_partial_write without id).
-            $this->logPartial('', 'Anlegen abgebrochen; Entwurf möglicherweise vorhanden');
+            $this->logPartial('', sprintf('Anlegen abgebrochen; %s möglicherweise vorhanden', $this->noun));
             throw WriteFailed::partial(self::REASON_INSERT, $e);
         }
         if ($postId instanceof WP_Error) {
@@ -77,7 +80,7 @@ final class NewDraft
         }
 
         if (! $deleted) {
-            $summary = sprintf('Entwurf %d: Anlegen nicht zurückgenommen', $postId);
+            $summary = sprintf('%s %d: Anlegen nicht zurückgenommen', $this->noun, $postId);
             $this->logPartial((string) $postId, $summary);
             $fields = $denied instanceof WP_Error ? Errors::fieldsOf($denied) : $denied;
             throw WriteFailed::partial(
@@ -102,7 +105,7 @@ final class NewDraft
     public function discard(int $postId, Throwable $cause, string $reason): never
     {
         $problems = Rollback::attempt(
-            fn () => $this->writer->deleteCreatedTerms(),
+            fn () => $this->writer?->deleteCreatedTerms(),
             static fn () => self::deleteDraft($postId)
         );
 
@@ -111,7 +114,7 @@ final class NewDraft
             throw WriteFailed::rolledBack($reason, $cause, $detail);
         }
 
-        $summary = sprintf('Entwurf %d: Anlegen nur teilweise zurückgenommen', $postId);
+        $summary = sprintf('%s %d: Anlegen nur teilweise zurückgenommen', $this->noun, $postId);
         $this->logPartial((string) $postId, $summary);
         throw WriteFailed::partial($reason, $cause, $detail . '; rollback: ' . implode('; ', $problems), $postId);
     }