refactor: WriteFailed named constructors, Rollback runner, Errors read-back helpers (H6)

- WriteFailed::rolledBack()/partial() replace the 11-parameter constructor (now
  private); the hint/state of either error are plain $hint/$state.
- Rollback::attempt(...steps) runs every undo step and collects failure messages;
  used by ContentCreate::discard, ContentUpdate::rollBack, MediaUpdate::rollBack and
  DiviSaver::restore.
- Errors::clientMessage/codeOf/fieldsOf replace DiviReplaceTextAbility::reason,
  the JSON digging in MediaUpdateAbility::failure and ContentCreateAbility::fields.
- Errors docblock documents the exception/WP_Error split.
- ContentCreateAbility::discard takes the client reason as a parameter (both callers
  still pass REASON_EXTRAS; changing the Divi text needs a ruling).

Error payloads unchanged.

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

src/Integrations/WordPress/Content/ContentCreateAbility.php

@@ -7,12 +7,14 @@ namespace LIT\MCP\Integrations\WordPress\Content;
 use LIT\MCP\Abilities\Ability;
 use LIT\MCP\Abilities\Errors;
 use LIT\MCP\Abilities\Rev;
+use LIT\MCP\Abilities\Rollback;
 use LIT\MCP\Abilities\ToolResult;
 use LIT\MCP\Abilities\WriteFailed;
 use LIT\MCP\ChangeLog\ChangeLog;
 use LIT\MCP\Integrations\WordPress\PostChangeResult;
 use LIT\MCP\Integrations\WordPress\PostGuard;
 use LIT\MCP\Integrations\WordPress\Schema\ContentSchema;
+use RuntimeException;
 use Throwable;
 use WP_Error;
 use WP_Post;
@@ -137,7 +139,7 @@ final class ContentCreateAbility implements Ability
             // 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).
             $this->logPartial($postType, '', 'Anlegen abgebrochen; Entwurf möglicherweise vorhanden');
-            throw new WriteFailed(self::REASON_INSERT, false, null, null, $e);
+            throw WriteFailed::partial(self::REASON_INSERT, $e);
         }
         if ($postId instanceof WP_Error) {
             return Errors::invalidInput('WordPress hat den Eintrag abgelehnt: ' . $postId->get_error_message());
@@ -153,7 +155,7 @@ final class ContentCreateAbility implements Ability
         try {
             $layout = $withDivi ? $this->divi?->write($postId, $postType, self::sections($input)) : null;
         } catch (Throwable $e) {
-            $this->discard($postId, $postType, $e);
+            $this->discard($postId, $postType, $e, self::REASON_EXTRAS);
         }
         if ($layout instanceof WP_Error) {
             return $this->refuse($postId, $postType, $layout);
@@ -162,7 +164,7 @@ final class ContentCreateAbility implements Ability
         try {
             $this->writer->writeExtras($postId, $postType, $prepared, $input);
         } catch (Throwable $e) {
-            $this->discard($postId, $postType, $e);
+            $this->discard($postId, $postType, $e, self::REASON_EXTRAS);
         }
 
         $warnings = array_merge($prepared['warnings'], $layout['warnings'] ?? []);
@@ -207,7 +209,7 @@ final class ContentCreateAbility implements Ability
             return $prepared instanceof WP_Error ? $prepared : $divi;
         }
 
-        $fields = array_merge(self::fields($prepared), self::fields($divi));
+        $fields = array_merge(Errors::fieldsOf($prepared), Errors::fieldsOf($divi));
         if ($fields === []) {
             return $prepared;
         }
@@ -217,14 +219,6 @@ final class ContentCreateAbility implements Ability
             : Errors::invalidInput('Eingaben sind ungültig; nichts wurde angelegt.', $fields);
     }
 
-    /** @return array<string, string> */
-    private static function fields(WP_Error $error): array
-    {
-        $data = $error->get_error_data();
-
-        return is_array($data) && is_array($data['fields'] ?? null) ? $data['fields'] : [];
-    }
-
     /**
      * @param array<string, mixed> $input
      * @param list<string>         $warnings
@@ -254,42 +248,38 @@ final class ContentCreateAbility implements Ability
 
     /**
      * Rolls the brand-new draft back: terms it created, then the draft itself (force –
-     * it cannot have been used anywhere yet).
+     * it cannot have been used anywhere yet). $reason is the client text of the error.
      *
      * @throws WriteFailed Always.
      */
-    private function discard(int $postId, string $postType, Throwable $cause): never
+    private function discard(int $postId, string $postType, Throwable $cause, string $reason): never
     {
-        $problems = [];
-        try {
-            $this->writer->deleteCreatedTerms();
-        } catch (Throwable $e) {
-            $problems[] = $e->getMessage();
-        }
-
-        try {
-            if (! wp_delete_post($postId, true)) {
-                $problems[] = sprintf('draft %d could not be deleted', $postId);
+        $problems = Rollback::attempt(
+            fn () => $this->writer->deleteCreatedTerms(),
+            static function () use ($postId): void {
+                try {
+                    $deleted = wp_delete_post($postId, true);
+                } catch (Throwable $e) {
+                    throw new RuntimeException(
+                        sprintf('draft %d could not be deleted: %s', $postId, $e->getMessage()),
+                        0,
+                        $e
+                    );
+                }
+                if (! $deleted) {
+                    throw new RuntimeException(sprintf('draft %d could not be deleted', $postId));
+                }
             }
-        } catch (Throwable $e) {
-            $problems[] = sprintf('draft %d could not be deleted: %s', $postId, $e->getMessage());
-        }
+        );
 
         $detail = sprintf('Extras of new post %d could not be written: %s', $postId, $cause->getMessage());
         if ($problems === []) {
-            throw new WriteFailed(self::REASON_EXTRAS, true, null, null, $cause, $detail);
+            throw WriteFailed::rolledBack($reason, $cause, $detail);
         }
 
         $summary = sprintf('Entwurf %d: Anlegen nur teilweise zurückgenommen', $postId);
         $this->logPartial($postType, (string) $postId, $summary);
-        throw new WriteFailed(
-            self::REASON_EXTRAS,
-            false,
-            $postId,
-            null,
-            $cause,
-            $detail . '; rollback: ' . implode('; ', $problems)
-        );
+        throw WriteFailed::partial($reason, $cause, $detail . '; rollback: ' . implode('; ', $problems), $postId);
     }
 
     /**
@@ -311,15 +301,12 @@ final class ContentCreateAbility implements Ability
         if (! $deleted) {
             $summary = sprintf('Entwurf %d: Anlegen nicht zurückgenommen', $postId);
             $this->logPartial($postType, (string) $postId, $summary);
-            $fields = $denied instanceof WP_Error ? self::fields($denied) : $denied;
-            throw new WriteFailed(
+            $fields = $denied instanceof WP_Error ? Errors::fieldsOf($denied) : $denied;
+            throw WriteFailed::partial(
                 ($denied instanceof WP_Error ? 'Ungültiger Divi-Inhalt: ' : 'Keine Berechtigung für ')
                     . implode(', ', array_keys($fields)) . '.',
-                false,
-                $postId,
-                null,
-                null,
-                sprintf('New post %d refused after the insert; draft could not be deleted', $postId)
+                detail: sprintf('New post %d refused after the insert; draft could not be deleted', $postId),
+                postId: $postId
             );
         }