Upd save chunk sclicer

memory.py

@@ -26,7 +26,9 @@ class MemoryManager:
     # ---------- Public API ----------
     def add_exchange(self, user_id: str, query: str, response: str, lang: str = "EN"):
         self._touch_user(user_id)
-        self.text_cache[user_id].append((query.strip(), response.strip()))
+        self.text_cache[user_id].append(((query or "").strip(), (response or "").strip()))
+        if not response:
+            return []
         # Avoid re-chunking identical response
         cache_key = hashlib.md5((query + response).encode()).hexdigest()
         if cache_key in self.chunk_cache: