feat: structure and content fingerprints, lit/library-find-similar

Fingerprint::structure()/content() (E11) and lit/library-find-similar
(indirect, group Divi-Bibliothek): at most 200 posts per call (cursor),
editable entries only (own posts without edit_others_posts), contents
primed in chunks of 50, stops at 200 matches or 5000 compared nodes with
a note; library entries and Theme Builder layouts are never scanned.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Integrations/Divi/BlockTree/Fingerprint.php

@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Integrations\Divi\BlockTree;
+
+use stdClass;
+
+defined('ABSPATH') || exit;
+
+/**
+ * Fingerprints of a node (E11) for lit/library-find-similar, the "similar section" warning (spec §5.5) and
+ * lit/library-make-global. structure(): block names and nesting, column layout (flexType) and preset IDs – two
+ * sections built alike with other texts share it. content(): every attribute but the admin label,
+ * builderVersion and globalParent, children included – "the same section". Whitespace between blocks never
+ * counts; an opaque block counts by its raw opener (content) or its effective type (structure). Pure PHP.
+ */
+final class Fingerprint
+{
+    /** Top-level attributes that say nothing about what visitors see. */
+    private const IGNORED = ['builderVersion', 'globalParent'];
+
+    public static function structure(Block $block): string
+    {
+        return self::hash(self::shape($block));
+    }
+
+    public static function content(Block $block): string
+    {
+        return self::hash(self::body($block));
+    }
+
+    private static function shape(Block $block): string
+    {
+        if ($block->isOpaque()) {
+            return 'opaque:' . GlobalInstance::effectiveName($block);
+        }
+
+        $presets = NodeSummary::presetIds($block);
+        sort($presets);
+        $children = array_map(self::shape(...), $block->children());
+
+        return $block->name() . '|' . (NodeSummary::columnWidth($block) ?? '') . '|' . implode(',', $presets)
+            . '[' . implode(';', $children) . ']';
+    }
+
+    private static function body(Block $block): string
+    {
+        if ($block->isOpaque()) {
+            return 'opaque:' . (string) $block->rawOpen();
+        }
+
+        $attrs = $block->attrs();
+        foreach (self::IGNORED as $key) {
+            unset($attrs[$key]);
+        }
+        if (is_array($attrs['module']['meta'] ?? null)) {
+            unset($attrs['module']['meta']['adminLabel']);
+        }
+        $children = array_map(self::body(...), $block->children());
+
+        return $block->name() . Json::encode(self::sorted($attrs)) . '[' . implode(';', $children) . ']';
+    }
+
+    /** Object keys sorted at every depth, so the key order Divi or the plugin wrote does not count. */
+    private static function sorted(mixed $value): mixed
+    {
+        if ($value instanceof stdClass) {
+            $value = (array) $value;
+        }
+        if (! is_array($value)) {
+            return $value;
+        }
+        if (! array_is_list($value)) {
+            ksort($value);
+        }
+
+        return array_map(self::sorted(...), $value);
+    }
+
+    private static function hash(string $value): string
+    {
+        return substr(hash('sha256', $value), 0, 16);
+    }
+}