Update app.py

app.py

@@ -231,6 +231,10 @@ def get_file(source_documents):
 # # ── Build once at startup (not per Gradio call) ───────────────────────────────
 # chain, retriever = build_chain(vectordb)   # vectordb initialised elsewhere
 
+retriever = vectordb.as_retriever(
+        search_type="mmr",
+        search_kwargs={"k": 3, "lambda_mult": 0.5, "fetch_k": 15},
+    
 
 # Query Re-write
 def rewrite_query(question: str, llm) -> str: