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>

tests/Unit/Abilities/AbilityRegistrarTest.php

@@ -182,7 +182,12 @@ final class AbilityRegistrarTest extends TestCase
         $previous = ini_set('error_log', $log);
         $ability = $this->ability();
         $ability->expects('execute')->andThrow(
-            new WriteFailed('Felder konnten nicht gespeichert werden.', false, 5, 811, new RuntimeException('meta /var/www'))
+            WriteFailed::partial(
+                'Felder konnten nicht gespeichert werden.',
+                new RuntimeException('meta /var/www'),
+                postId: 5,
+                revisionId: 811
+            )
         );
 
         try {

tests/Unit/Abilities/ErrorsTest.php

@@ -114,4 +114,24 @@ final class ErrorsTest extends TestCase
         self::assertStringContainsString('Entwurf', $payload['message']);
         self::assertArrayNotHasKey('post_id', $payload);
     }
+
+    public function testClientMessageReadsTheJsonMessageBack(): void
+    {
+        self::assertSame('Titel fehlt.', Errors::clientMessage(Errors::invalidInput('Titel fehlt.')));
+        self::assertSame('WordPress sagt nein', Errors::clientMessage(new \WP_Error('db', 'WordPress sagt nein')));
+        self::assertSame('{"code":"x"}', Errors::clientMessage(new \WP_Error('db', '{"code":"x"}')));
+    }
+
+    public function testCodeOfDropsTheLitPrefixOnly(): void
+    {
+        self::assertSame('validation_failed', Errors::codeOf(Errors::invalidInput('x')));
+        self::assertSame('db_error', Errors::codeOf(new \WP_Error('db_error', 'x')));
+    }
+
+    public function testFieldsOfReturnsTheFieldsOrNothing(): void
+    {
+        self::assertSame(['title' => 'Pflichtfeld'], Errors::fieldsOf(Errors::invalidInput('x', ['title' => 'Pflichtfeld'])));
+        self::assertSame([], Errors::fieldsOf(Errors::invalidInput('x')));
+        self::assertSame([], Errors::fieldsOf(new \WP_Error('db', 'x', 'kein Array')));
+    }
 }

tests/Unit/Abilities/RollbackTest.php

@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Tests\Unit\Abilities;
+
+use LIT\MCP\Abilities\Rollback;
+use LIT\MCP\Tests\Unit\TestCase;
+use RuntimeException;
+
+final class RollbackTest extends TestCase
+{
+    public function testAllStepsRunInOrderAndNothingFailed(): void
+    {
+        $ran = [];
+
+        $failures = Rollback::attempt(
+            static function () use (&$ran): void {
+                $ran[] = 1;
+            },
+            static function () use (&$ran): void {
+                $ran[] = 2;
+            }
+        );
+
+        self::assertSame([], $failures);
+        self::assertSame([1, 2], $ran);
+    }
+
+    public function testAFailingStepDoesNotStopTheOthersAndItsMessageIsCollected(): void
+    {
+        $ran = [];
+
+        $failures = Rollback::attempt(
+            static function (): void {
+                throw new RuntimeException('Begriffe nicht gelöscht');
+            },
+            static function () use (&$ran): void {
+                $ran[] = 2;
+            },
+            static function (): void {
+                throw new \Error('Zeile nicht zurückgesetzt');
+            }
+        );
+
+        self::assertSame(['Begriffe nicht gelöscht', 'Zeile nicht zurückgesetzt'], $failures);
+        self::assertSame([2], $ran);
+    }
+
+    public function testAReturnValueIsNoFailure(): void
+    {
+        self::assertSame([], Rollback::attempt(static fn (): string => 'egal', static fn (): bool => false));
+    }
+}

tests/Unit/Abilities/WriteFailedTest.php

@@ -13,7 +13,7 @@ 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);
+        $failure = WriteFailed::rolledBack('Felder konnten nicht gespeichert werden.', $cause, postId: 5);
 
         self::assertTrue($failure->rolledBack);
         self::assertSame($cause, $failure->getPrevious());
@@ -23,16 +23,17 @@ final class WriteFailedTest extends TestCase
 
     public function testRolledBackHintReplacesTheDefaultHintOfWriteFailedOnly(): void
     {
-        $clean = new WriteFailed('x', true, rolledBackHint: 'Erst neu lesen.');
-        $partial = new WriteFailed('x', false, rolledBackHint: 'Erst neu lesen.');
+        $clean = WriteFailed::rolledBack('x', hint: 'Erst neu lesen.');
+        $partial = WriteFailed::partial('x');
 
         self::assertSame('Erst neu lesen.', $clean->toError()->get_error_data()['hint']);
         self::assertNotSame('Erst neu lesen.', $partial->toError()->get_error_data()['hint']);
+        self::assertStringStartsWith('Den Aufruf nicht einfach wiederholen.', $partial->toError()->get_error_data()['hint']);
     }
 
     public function testIncompleteRollbackMapsToPartialWriteWithTheIds(): void
     {
-        $error = (new WriteFailed('Felder konnten nicht gespeichert werden.', false, 5, 811))->toError();
+        $error = WriteFailed::partial('Felder konnten nicht gespeichert werden.', postId: 5, revisionId: 811)->toError();
 
         self::assertSame('lit_partial_write', $error->get_error_code());
         self::assertSame(5, $error->get_error_data()['post_id']);
@@ -41,13 +42,12 @@ final class WriteFailedTest extends TestCase
 
     public function testIncompleteRollbackCanDescribeItsOwnStateHintAndDetails(): void
     {
-        $error = (new WriteFailed(
+        $error = WriteFailed::partial(
             'Menü nicht gespeichert.',
-            false,
             state: 'Das Menü ist teilweise geändert.',
             hint: 'Mit lit/menu-get prüfen.',
             details: ['menu_id' => 3]
-        ))->toError();
+        )->toError();
 
         self::assertSame('lit_partial_write', $error->get_error_code());
         self::assertStringContainsString('Das Menü ist teilweise geändert.', $error->get_error_message());
@@ -59,8 +59,8 @@ final class WriteFailedTest extends TestCase
     public function testRolledBackStateReplacesNothingWasSavedOfWriteFailedOnly(): void
     {
         $state = 'Die Änderung wurde nicht gespeichert (Sicherung 88 bleibt erhalten).';
-        $clean = (new WriteFailed('x', true, rolledBackState: $state))->toError();
-        $partial = (new WriteFailed('x', false, rolledBackState: $state))->toError();
+        $clean = WriteFailed::rolledBack('x', state: $state)->toError();
+        $partial = WriteFailed::partial('x')->toError();
 
         self::assertStringContainsString($state, $clean->get_error_message());
         self::assertStringNotContainsString('Nichts wurde gespeichert', $clean->get_error_message());
@@ -69,10 +69,31 @@ final class WriteFailedTest extends TestCase
 
     public function testCleanRollbackKeepsItsDetails(): void
     {
-        $error = (new WriteFailed('Nicht übernommen.', true, details: ['backup_id' => 88]))->toError();
+        $error = WriteFailed::rolledBack('Nicht übernommen.', details: ['backup_id' => 88])->toError();
 
         self::assertSame('lit_write_failed', $error->get_error_code());
         self::assertSame(88, $error->get_error_data()['backup_id']);
         self::assertStringContainsString('"backup_id":88', $error->get_error_message());
     }
+
+    public function testTheLogMessageIsTheDetailOrTheCauseOrTheReasonWithTheRollbackOutcome(): void
+    {
+        $cause = new RuntimeException('meta kaputt');
+
+        self::assertSame('Detail [rolled back]', WriteFailed::rolledBack('x', $cause, 'Detail')->getMessage());
+        self::assertSame('meta kaputt [rollback incomplete]', WriteFailed::partial('x', $cause)->getMessage());
+        self::assertSame('Grund [rolled back]', WriteFailed::rolledBack('Grund')->getMessage());
+    }
+
+    public function testTheNamedConstructorsKeepTheIdsForCallersThatLogThem(): void
+    {
+        $clean = WriteFailed::rolledBack('x', postId: 7, revisionId: 811);
+        $partial = WriteFailed::partial('x', postId: 7, revisionId: 811);
+
+        self::assertTrue($clean->rolledBack);
+        self::assertSame([7, 811], [$clean->postId, $clean->revisionId]);
+        self::assertFalse($partial->rolledBack);
+        self::assertSame([7, 811], [$partial->postId, $partial->revisionId]);
+        self::assertArrayNotHasKey('post_id', $clean->toError()->get_error_data());
+    }
 }