fix: Task 6 review round 2 - builder column classes, sum check only for exact rows, unknown path wins, column structure text (S43)

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

tests/Unit/Integrations/Divi/Compose/ComposerTest.php

@@ -261,6 +261,20 @@ final class ComposerTest extends TestCase
         self::assertStringContainsString('label', $update['errors']['changes[0].attrs.module.meta.adminLabel']);
     }
 
+    /** Ruling S43: an unknown path wins over the overlap message on the same key. */
+    public function testUnknownPathWinsOverOverlap(): void
+    {
+        $result = ComposeFixture::composer()->compose([[
+            'type' => 'heading',
+            'text' => 'x',
+            'label' => 'B',
+            'attrs' => ['module.meta' => ['desktop' => 'A']],
+        ]], Block::create('divi/column'), 'nodes');
+
+        self::assertSame(['module.meta'], $result['invalid_paths']);
+        self::assertStringContainsString('unbekannter Attributpfad', $result['errors']['nodes[0].attrs.module.meta']);
+    }
+
     /** Ruling S41: the default heading level survives attrs on the same font value. */
     public function testDefaultHeadingLevelIsMergedIntoAttrs(): void
     {