Rather than explicitly checking to see if the user
was typing a shell exit command, the LLM is now
instructed to provide a specific token starting
("XXX-END-OF-SESSION-XXX") to indicate that the
session should be closed. This allows the user to
exit the shell in any way they see fit, and the
LLM will still know when to end the session. It
also means that typing 'exit' or similar commands
to subshells or command interpreters (e.g. Python)
are less likely to cause the session to end.
