How can I make a PDF chatbot that keeps the context of each access separate?

I’m a beginner user of Streamlit and I’ve created a chatbot with Gemini to ask questions in the context of .PDF files.
The Github is here (app.py). It works well, but I’ve noticed that when two or more users use the site at the same time, the context of the answers is mixed up
That is, user 1 uploads a PDF and starts asking the model questions about a topic. Then user 2, on another computer, uploads another PDF on another subject. User 1’s answers start to have user 2’s context
So I want to know if Streamlit can isolate the context of each user who uses the chatbot.