if (markdownDomPurifyInitialized || typeof DOMPurify === 'undefined') return;
        // Register hook once: add rel="nofollow" to links, restrict class to code/pre/span/div
        // (matches server-side requireRelNofollowOnLinks and allowAttributes("class").onElements(...))
        DOMPurify.addHook('afterSanitizeAttributes', function(node) {
            if (node.tagName === 'A' && node.hasAttribute('href')) {