Support multiple file uploads in chatbot

Currently, our chat bot built using calstudio.com only allows for single file uploads: if a user uploads a new file, it replaces the previous one. We need a feature that enables users to upload multiple files successively, so that all uploaded files remain visible and accessible.
Example use-case: User uploads ‘file1.pdf’, then uploads ‘file2.docx’ — both files should be visible in the chat, not just the last one.