diff --git a/src/ApiKernel.php b/src/ApiKernel.php
index fc1ff29..40a0346 100644
--- a/src/ApiKernel.php
+++ b/src/ApiKernel.php
@@ -1,6 +1,8 @@
 <?php
 declare(strict_types=1);
 
+use DOMDocument;
+use DOMXPath;
 use TijsVerkoyen\CssToInlineStyles\CssToInlineStyles;
 
 // 💡 NEUE KORREKTUR: Starte Output Buffering so früh wie möglich, um Whitespace/Errors
@@ -659,6 +661,10 @@ class ApiKernel
         if ($html === '' && !empty($row['json_content'])) {
             $html = '<p>(Dieses Template enthält noch keine HTML-Inhalte.)</p>';
         }
+
+        $renderCache = [];
+        $renderStack = [];
+        $html = $this->renderHtmlWithReferences($html, $auth, $renderCache, $renderStack);
         $html = $this->prepareEmailHtml($html);
 
         if (!$this->dispatchTestMail($recipient, $subject, $html)) {
@@ -867,4 +873,119 @@ class ApiKernel
         $summary['total'] = array_sum($summary);
         return $summary;
     }
+
+    private function normalizeResourceKind(string $kind): ?string
+    {
+        $kind = strtolower(trim($kind));
+        $map = [
+            'template' => 'templates',
+            'templates' => 'templates',
+            'section' => 'sections',
+            'sections' => 'sections',
+            'block' => 'blocks',
+            'blocks' => 'blocks',
+            'snippet' => 'snippets',
+            'snippets' => 'snippets',
+        ];
+        return $map[$kind] ?? null;
+    }
+
+    private function resolveHtmlColumn(array $columns, string $kindKey): ?string
+    {
+        $candidates = ($kindKey === 'snippets')
+            ? ['content', 'html', 'body', 'markup']
+            : ['html', 'body', 'markup', 'content'];
+        return $this->firstExisting($columns, $candidates);
+    }
+
+    private function fetchResourceHtml(string $kind, int $id, array $auth, array &$cache, array &$stack): ?string
+    {
+        $kindKey = $this->normalizeResourceKind($kind);
+        if (!$kindKey || $id <= 0) return null;
+
+        $cacheKey = $kindKey . ':' . $id;
+        if (array_key_exists($cacheKey, $cache)) return $cache[$cacheKey];
+        if (!empty($stack[$cacheKey])) return null;
+
+        $table = $this->tableMap[$kindKey] ?? null;
+        if (!$table) return null;
+        [$idCol, $allCols] = $this->resolveIdCol($kindKey);
+        [$tw, $tp] = $this->tenantWhere($auth);
+
+        $sql = "SELECT * FROM `$table` WHERE `$idCol` = :id" . $tw . " LIMIT 1";
+        $stmt = $this->pdo->prepare($sql);
+        $stmt->bindValue(':id', $id);
+        foreach ($tp as $k => $v) $stmt->bindValue($k, $v);
+        $stmt->execute();
+        $row = $stmt->fetch();
+        if (!$row) {
+            $cache[$cacheKey] = null;
+            return null;
+        }
+
+        $htmlCol = $this->resolveHtmlColumn($allCols, $kindKey);
+        $html = $htmlCol && isset($row[$htmlCol]) ? (string)$row[$htmlCol] : '';
+
+        $stack[$cacheKey] = true;
+        $html = $this->renderHtmlWithReferences($html, $auth, $cache, $stack);
+        unset($stack[$cacheKey]);
+
+        $cache[$cacheKey] = $html;
+        return $html;
+    }
+
+    private function renderHtmlWithReferences(string $html, array $auth, array &$cache, array &$stack): string
+    {
+        $trimmed = trim($html);
+        if ($trimmed === '') return $html;
+        if (!class_exists(DOMDocument::class)) return $html;
+
+        $flags = 0;
+        if (defined('LIBXML_HTML_NOIMPLIED')) {
+            $flags |= LIBXML_HTML_NOIMPLIED;
+        }
+        if (defined('LIBXML_HTML_NODEFDTD')) {
+            $flags |= LIBXML_HTML_NODEFDTD;
+        }
+
+        $doc = new DOMDocument('1.0', 'UTF-8');
+        libxml_use_internal_errors(true);
+        $wrapper = '<div id="lib-ref-root">' . $html . '</div>';
+        $loaded = @$doc->loadHTML('<?xml encoding="utf-8"?>' . $wrapper, $flags);
+        libxml_clear_errors();
+        if (!$loaded) return $html;
+
+        $xpath = new DOMXPath($doc);
+        $nodes = $xpath->query('//*[@data-lib-kind and @data-lib-id]');
+        if ($nodes !== false) {
+            foreach ($nodes as $node) {
+                /** @var \DOMElement $node */
+                $kind = $node->getAttribute('data-lib-kind');
+                $refId = (int)$node->getAttribute('data-lib-id');
+                if (!$kind || $refId <= 0) continue;
+                $replacement = $this->fetchResourceHtml($kind, $refId, $auth, $cache, $stack);
+                if ($replacement === null) continue;
+
+                while ($node->firstChild) {
+                    $node->removeChild($node->firstChild);
+                }
+
+                $fragment = $doc->createDocumentFragment();
+                if (@$fragment->appendXML($replacement)) {
+                    $node->appendChild($fragment);
+                } else {
+                    $node->appendChild($doc->createTextNode($replacement));
+                }
+            }
+        }
+
+        $root = $doc->getElementById('lib-ref-root');
+        if (!$root) return $html;
+
+        $output = '';
+        foreach ($root->childNodes as $child) {
+            $output .= $doc->saveHTML($child);
+        }
+        return $output;
+    }
 }