fix(reader): clear markdown render on change and add request guards to external URL loader to prevent stale content

src/hooks/useMarkdownToHTML.ts

@@ -20,9 +20,11 @@ export const useMarkdownToHTML = (
   const [processedMarkdown, setProcessedMarkdown] = useState<string>('')
 
   useEffect(() => {
+    // Always clear previous render immediately to avoid showing stale content while processing
+    setRenderedHtml('')
+    setProcessedMarkdown('')
+    
     if (!markdown) {
-      setRenderedHtml('')
-      setProcessedMarkdown('')
       return
     }