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

tests/Unit/Abilities/WriteFailedTest.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Tests\Unit\Abilities;
+
+use LIT\MCP\Abilities\WriteFailed;
+use LIT\MCP\Tests\Unit\TestCase;
+use RuntimeException;
+
+final class WriteFailedTest extends TestCase
+{
+    public function testCleanRollbackMapsToWriteFailed(): void
+    {
+        $cause = new RuntimeException('meta kaputt');
+        $failure = new WriteFailed('Felder konnten nicht gespeichert werden.', true, 5, null, $cause);
+
+        self::assertTrue($failure->rolledBack);
+        self::assertSame($cause, $failure->getPrevious());
+        self::assertStringContainsString('meta kaputt', $failure->getMessage());
+        self::assertSame('lit_write_failed', $failure->toError()->get_error_code());
+    }
+
+    public function testIncompleteRollbackMapsToPartialWriteWithTheIds(): void
+    {
+        $error = (new WriteFailed('Felder konnten nicht gespeichert werden.', false, 5, 811))->toError();
+
+        self::assertSame('lit_partial_write', $error->get_error_code());
+        self::assertSame(5, $error->get_error_data()['post_id']);
+        self::assertSame(811, $error->get_error_data()['revision_id']);
+    }
+}