Update app.py

app.py

@@ -2,7 +2,14 @@ import streamlit as st
 import os
 import subprocess
 from streamlit_pdf_viewer import pdf_viewer
+import shutil
 
+# Add this right after your imports
+if not shutil.which("pdflatex"):
+    st.error("❌ LaTeX compiler not found!")
+    st.info("If you are on HuggingFace/Streamlit Cloud, make sure 'packages.txt' is in the root directory and contains 'texlive-latex-base'.")
+    st.stop()
+    
 # --- Configuration ---
 TOPICS_DIR = "topics"
 TEMP_DIR = "temp_build"