Adding streaming and a persona

Two upgrades that take the app from "okay" to "feels like ChatGPT". Both are 5 minutes of work.

Adding wheels to a chair. Tiny change, totally different experience.

Streaming: convert the OpenAI call to stream=True and update the UI as tokens arrive.

Persona: prepend a system message to st.session_state.messages.

Replace the API call section with:

SYSTEM = (
    "You are GeekBot, a friendly tech tutor for beginners. "
    "Reply in short, clear paragraphs. Use simple analogies."
)

# Ensure system message is first
if not st.session_state.messages or st.session_state.messages[0]["role"] != "system":
    st.session_state.messages.insert(0, {"role": "system", "content": SYSTEM})

if prompt := st.chat_input("Ask me anything"):
    st.session_state.messages.append({"role": "user", "content": prompt})
    with st.chat_message("user"):
        st.markdown(prompt)

    with st.chat_message("assistant"):
        placeholder = st.empty()
        stream = client.chat.completions.create(
            model="gpt-4o-mini",
            messages=st.session_state.messages,
            stream=True,
        )
        text = ""
        for chunk in stream:
            delta = chunk.choices[0].delta.content
            if delta:
                text += delta
                placeholder.markdown(text + "_")
        placeholder.markdown(text)
        st.session_state.messages.append({"role": "assistant", "content": text})

Done. Live streaming and a custom persona.