diff --git a/tests/Fixtures/divi/synthetic-divi-filters.html b/tests/Fixtures/divi/synthetic-divi-filters.html
index 2103459..e310d16 100644
--- a/tests/Fixtures/divi/synthetic-divi-filters.html
+++ b/tests/Fixtures/divi/synthetic-divi-filters.html
@@ -1 +1 @@
-<!-- wp:divi/placeholder --><!-- wp:divi/section {"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder"}}}},"builderVersion":"5.2.1"} --><!-- wp:divi/row {"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Zeile"}}}},"builderVersion":"5.2.1"} --><!-- wp:divi/column {"module":{"decoration":{"sizing":{"desktop":{"value":{"flexType":"24_24"}}}}},"builderVersion":"5.2.1"} --><!-- wp:divi/text {"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Artikel"}}},"advanced":{"html":{"elementType":{"desktop":{"value":"article"}}}},"decoration":{"attributes":{"desktop":{"value":{"attributes":[{"id":"lit-attr-1","name":"data-track","value":"hero","targetElement":""}]}}}}},"content":{"innerContent":{"desktop":{"value":"<p>Text mit eigenem Element und Attribut.</p>"}}},"builderVersion":"5.2.1"} --><!-- /wp:divi/text --><!-- wp:divi/heading {"title":{"innerContent":{"desktop":{"value":"Eigene Felder bleiben"}},"decoration":{"font":{"font":{"desktop":{"value":{"headingLevel":"h2"}}}}}},"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Überschrift"}}}},"builderVersion":"5.2.1"} --><!-- /wp:divi/heading --><!-- wp:divi/button {"button":{"innerContent":{"desktop":{"value":{"text":"Kontakt","linkUrl":"/kontakt"}}}},"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Button"}}}},"builderVersion":"5.2.1"} --><!-- /wp:divi/button --><!-- /wp:divi/column --><!-- /wp:divi/row --><!-- /wp:divi/section --><!-- /wp:divi/placeholder -->
\ No newline at end of file
+<!-- wp:divi/placeholder --><!-- wp:divi/section {"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder"}}}},"builderVersion":"5.2.1"} --><!-- wp:divi/row {"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Zeile"}}}},"builderVersion":"5.2.1"} --><!-- wp:divi/column {"module":{"decoration":{"sizing":{"desktop":{"value":{"flexType":"24_24"}}}}},"builderVersion":"5.2.1"} --><!-- wp:divi/text {"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Artikel"}}},"advanced":{"html":{"elementType":{"desktop":{"value":"article"}}}},"decoration":{"attributes":{"desktop":{"value":{"attributes":[{"id":"lit-attr-1","name":"data-track","value":"hero","targetElement":""}]}}}}},"content":{"innerContent":{"desktop":{"value":"\u003cp\u003eText mit eigenem Element und Attribut.\u003c/p\u003e"}}},"builderVersion":"5.2.1"} --><!-- /wp:divi/text --><!-- wp:divi/heading {"title":{"innerContent":{"desktop":{"value":"Eigene Felder bleiben"}},"decoration":{"font":{"font":{"desktop":{"value":{"headingLevel":"h2"}}}}}},"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Überschrift"}}}},"builderVersion":"5.2.1"} --><!-- /wp:divi/heading --><!-- wp:divi/button {"button":{"innerContent":{"desktop":{"value":{"text":"Kontakt","linkUrl":"/kontakt"}}}},"module":{"meta":{"adminLabel":{"desktop":{"value":"Eigene Felder – Button"}}}},"builderVersion":"5.2.1"} --><!-- /wp:divi/button --><!-- /wp:divi/column --><!-- /wp:divi/row --><!-- /wp:divi/section --><!-- /wp:divi/placeholder -->
\ No newline at end of file
diff --git a/tests/Unit/Integrations/Divi/Pages/DiviEditorByteIdentityTest.php b/tests/Unit/Integrations/Divi/Pages/DiviEditorByteIdentityTest.php
new file mode 100644
index 0000000..ab2696e
--- /dev/null
+++ b/tests/Unit/Integrations/Divi/Pages/DiviEditorByteIdentityTest.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Tests\Unit\Integrations\Divi\Pages;
+
+use Brain\Monkey\Functions;
+use LIT\MCP\Abilities\Rev;
+use LIT\MCP\Integrations\Divi\BlockTree\NodeIndex;
+use LIT\MCP\Integrations\Divi\BlockTree\Parser;
+use LIT\MCP\Integrations\Divi\BlockTree\Serializer;
+use LIT\MCP\Integrations\Divi\Pages\DiviInsertAbility;
+use LIT\MCP\Tests\Support\DiviFixtures;
+use LIT\MCP\Tests\Support\DiviWriterFixture;
+use LIT\MCP\Tests\Unit\TestCase;
+
+/**
+ * Ruling P20 (regression): a user without unfiltered_html (editor) changes one place of a real page;
+ * every other byte stays (JSON unicode escapes of markup, CRLF, empty block pairs, instances, foreign
+ * blocks). The pages are read from the fixture files only (never written inline), so no tool in
+ * between can decode an escape sequence.
+ */
+final class DiviEditorByteIdentityTest extends TestCase
+{
+    /** @return array<string, array{string}> */
+    public static function pages(): array
+    {
+        $pages = [];
+        foreach (['', 'stage3/'] as $dir) {
+            foreach (glob(dirname(__DIR__, 4) . '/Fixtures/divi/' . $dir . '*.html') ?: [] as $file) {
+                $name = $dir . basename($file);
+                if ($name !== 'divi4-shortcodes.html') {
+                    $pages[$name] = [$name];
+                }
+            }
+        }
+
+        return $pages;
+    }
+
+    /** @dataProvider pages */
+    public function testAnEditorInsertKeepsEveryOtherByte(string $fixture): void
+    {
+        $original = DiviFixtures::markup($fixture);
+        self::assertNotSame('', $original, $fixture);
+        DiviFixtures::givenPost($original);
+        Functions\when('get_preview_post_link')->justReturn('https://kunde.test/?page_id=7&preview=true');
+        $saved = [];
+
+        $result = (new DiviInsertAbility(DiviWriterFixture::writer($saved, unfiltered: false)))->execute([
+            'post_id' => 7,
+            'tree_rev' => Rev::of($original),
+            'nodes' => [['type' => 'section']],
+        ]);
+
+        self::assertTrue($result['ok'] ?? false, $fixture . ': ' . json_encode($result));
+        self::assertCount(1, $saved);
+        $node = NodeIndex::build((new Parser())->parse($saved[0]))->find($result['changed'][0]['id']);
+        self::assertNotNull($node, $fixture);
+        $inserted = Serializer::block($node);
+        $at = strpos($saved[0], $inserted);
+        self::assertNotFalse($at, $fixture);
+        self::assertSame(
+            $original,
+            substr($saved[0], 0, (int) $at) . substr($saved[0], (int) $at + strlen($inserted)),
+            $fixture . ': only the new section was added'
+        );
+    }
+}