app_echo.py

import streamlit as st

st.title('Echo Bot')

if "messages" not in st.session_state:
    st.session_state.messages = []

for message in st.session_state.messages:
    with st.chat_message(message['role']):
        st.markdown(message['content'])

prompt = st.chat_input('How can I help you?')
if prompt:
    with st.chat_message('user'):
        st.markdown(prompt)

    st.session_state.messages.append({'role': 'user', 'content': prompt})

    response = f'**Echo**: {prompt}'

    with st.chat_message('assistant'):
        st.markdown(response)

    st.session_state.messages.append({'role': 'assistant', 'content': response})