fix: typed write failures, template rollback, parent and term cleanup

WriteFailed maps to lit_write_failed / lit_partial_write (partial writes are
logged with result partial); old template read before the update; row marker
set before wp_update_post; created terms deleted on rollback; parent must be a
readable non-descendant of a hierarchical type; featured image must be
readable; snapshot keeps empty values; meta comparison after sanitize_meta;
follow-up failures (listener, change log) only add warnings.

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

src/Abilities/AbilityRegistrar.php

@@ -71,6 +71,10 @@ final class AbilityRegistrar
             'execute_callback' => static function (mixed $input = null) use ($ability): mixed {
                 try {
                     return $ability->execute(is_array($input) ? $input : []);
+                } catch (WriteFailed $e) {
+                    $message = sprintf('[wp-lit-mcp] %s failed: %s', $ability->name(), $e);
+                    error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+                    return $e->toError();
                 } catch (Throwable $e) {
                     $message = sprintf('[wp-lit-mcp] %s failed: %s', $ability->name(), $e);
                     error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log

src/Abilities/Errors.php

@@ -98,6 +98,44 @@ final class Errors
         return self::make('unsupported', $message, $hint, 400);
     }
 
+    /** A write failed and was rolled back completely. */
+    public static function writeFailed(string $reason): WP_Error
+    {
+        return self::make(
+            'write_failed',
+            trim('Speichern fehlgeschlagen: ' . $reason) . ' Nichts wurde gespeichert.',
+            'Eingaben prüfen, ggf. korrigieren und erneut versuchen; tritt der Fehler wieder auf, den Administrator '
+                . 'informieren (Details im PHP-Error-Log der Website).',
+            500
+        );
+    }
+
+    /**
+     * A write failed and could not be rolled back completely – something may have been saved.
+     */
+    public static function partialWrite(string $reason, ?int $postId = null, ?int $revisionId = null): WP_Error
+    {
+        $state = $postId === null
+            ? 'Möglicherweise wurde trotzdem ein Entwurf angelegt.'
+            : sprintf('Eintrag %d ist möglicherweise teilweise geändert bzw. angelegt worden', $postId)
+                . ($revisionId === null ? '.' : sprintf(' (Stand vorher: Revision %d).', $revisionId));
+        $details = array_filter(
+            ['post_id' => $postId, 'revision_id' => $revisionId],
+            static fn (?int $id): bool => $id !== null
+        );
+
+        return self::make(
+            'partial_write',
+            trim('Speichern fehlgeschlagen: ' . $reason) . ' Die Änderung konnte nicht vollständig zurückgenommen '
+                . 'werden. ' . $state,
+            'Den Aufruf nicht einfach wiederholen. Zuerst den aktuellen Stand prüfen (lit-content-get, bei einem '
+                . 'neuen Entwurf lit-content-query) und ggf. über lit-revisions-list den vorherigen Stand '
+                . 'wiederherstellen; dem Nutzer Bescheid geben.',
+            500,
+            $details
+        );
+    }
+
     public static function internal(): WP_Error
     {
         return self::make(

src/Abilities/FollowUp.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Abilities;
+
+use Throwable;
+
+/**
+ * Runs a step after a write has already succeeded (listeners, change log): a failure
+ * there must not turn the saved change into an error. It is logged and reported as warning.
+ */
+final class FollowUp
+{
+    /**
+     * @param list<string> $warnings Receives $warning when the step fails.
+     */
+    public static function run(callable $step, string $context, string $warning, array &$warnings): mixed
+    {
+        try {
+            return $step();
+        } catch (Throwable $e) {
+            $message = sprintf('[wp-lit-mcp] %s failed: %s', $context, $e);
+            error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+            $warnings[] = $warning;
+
+            return null;
+        }
+    }
+}

src/Abilities/WriteFailed.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Abilities;
+
+use RuntimeException;
+use Throwable;
+use WP_Error;
+
+/**
+ * Thrown by write paths when saving failed after something may already have been
+ * written. getMessage() is the internal detail for the PHP error log; $reason is the
+ * client-safe German text. The AbilityRegistrar logs the detail and returns toError():
+ * lit_write_failed when everything was rolled back, lit_partial_write otherwise.
+ */
+final class WriteFailed extends RuntimeException
+{
+    public function __construct(
+        public readonly string $reason,
+        public readonly bool $rolledBack,
+        public readonly ?int $postId = null,
+        public readonly ?int $revisionId = null,
+        ?Throwable $previous = null,
+        string $detail = ''
+    ) {
+        $internal = $detail !== '' ? $detail : ($previous !== null ? $previous->getMessage() : $reason);
+        parent::__construct(
+            sprintf('%s [%s]', $internal, $rolledBack ? 'rolled back' : 'rollback incomplete'),
+            0,
+            $previous
+        );
+    }
+
+    public function toError(): WP_Error
+    {
+        return $this->rolledBack
+            ? Errors::writeFailed($this->reason)
+            : Errors::partialWrite($this->reason, $this->postId, $this->revisionId);
+    }
+}