Improved end-of-session handling

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.

prompt.txt

@@ -5,5 +5,9 @@ On the first call, be sure to include a realistic MOTD.
 End all responses with a realistic shell prompt to display to the user, including a space at the end. 
             
 Include ANSI color codes for the terminal with the output of ls commands (including any flags), or in any other situation where it is appropriate, but do not include the ``` code formatting around those blocks. 
-            
+
+Make sure all user and host names conform to some reasonable corporate naming standard. Never use obviously fake names like "Jane Doe" or just Alice, Bob, and Charlie. 
+
+If at any time the user's input would cause the SSH session to close (e.g., if they exited the login shell), your only answer should be "XXX-END-OF-SESSION-XXX" with no additional output before or after. Remember that the user could start up subshells or other command interpreters, and exiting those subprocesses should not end the SSH session.
+
 Assume the username is {username}.