feat: Divi BlockTree – byte-exact parser/serializer with round-trip fixtures

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

src/Integrations/Divi/BlockTree/Json.php

@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Integrations\Divi\BlockTree;
+
+use JsonException;
+use stdClass;
+
+/**
+ * JSON of block attributes. PHP arrays cannot tell an empty JSON object from an empty list,
+ * nor an object with the keys "0", "1", … from a list. decodeObject() therefore keeps such
+ * objects as stdClass, so a regenerated opener encodes them as {} again (Divi breaks on
+ * "[]" where it expects "{}" – see its EmptyArrayCorruptionMigration).
+ */
+final class Json
+{
+    /** @return array<string, mixed>|null Null when $json is not a JSON object. */
+    public static function decodeObject(string $json): ?array
+    {
+        try {
+            $value = json_decode($json, false, 512, JSON_THROW_ON_ERROR);
+        } catch (JsonException) {
+            return null;
+        }
+
+        if (! $value instanceof stdClass) {
+            return null;
+        }
+
+        $converted = self::fromJson($value);
+
+        return is_array($converted) ? $converted : [];
+    }
+
+    /** Converts json_decode(…, false) output: objects become arrays unless that would lose their object-ness. */
+    public static function fromJson(mixed $value): mixed
+    {
+        if ($value instanceof stdClass) {
+            $array = [];
+            foreach (get_object_vars($value) as $key => $item) {
+                $array[$key] = self::fromJson($item);
+            }
+
+            return $array === [] || array_is_list($array) ? (object) $array : $array;
+        }
+
+        if (is_array($value)) {
+            return array_map([self::class, 'fromJson'], $value);
+        }
+
+        return $value;
+    }
+
+    /** @throws JsonException */
+    public static function encode(mixed $value): string
+    {
+        // phpcs:ignore WordPress.WP.AlternativeFunctions.json_encode_json_encode -- pure PHP (spec §4.4).
+        return json_encode($value, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_THROW_ON_ERROR);
+    }
+}