@nthmost Thank you very much for your reply, and for pointing me to the new FAQ page.
This has led closer to the answer, although I think there is still something missing: how can streamlit be configured to access static assets at a relative URL - /myapp/static instead of /static? By contrast, when behind the reverse proxy, the stream is accessed by the streamlit app at /myapp/stream instead of /stream (which is what I would hope). /static is still requested from /static instead of /myapp/static though - is this different treatment of the two URLs by design?