After hg cloning the source and starting the demo, I pointed my Firefox 140.19.2esr browser at the localhost port the demo said to use. I logged in with demo/demo and got no response.  On the terminal from which the demo launched:

127.0.0.1 - - [18/May/2026 06:15:21] "GET /demo/ HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:21] "GET /demo/@@file/style.css HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:21] "GET /demo/@@file/classhelper.js HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:21] "GET /demo/@@file/datecopy.min.js HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:22] "GET /demo/rest HTTP/1.1" 403 -
127.0.0.1 - - [18/May/2026 06:15:22] "GET /favicon.ico HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:49] "POST /demo/ HTTP/1.1" 302 -
127.0.0.1 - - [18/May/2026 06:15:49] "GET /demo/?%40ok_message=Welcome+demo%21 HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:49] "GET /demo/rest HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:49] "GET /favicon.ico HTTP/1.1" 200 -
127.0.0.1 - - [18/May/2026 06:15:49] "GET /favicon.ico HTTP/1.1" 400 -
EXCEPTION AT Mon May 18 06:15:49 2026
Traceback (most recent call last):
  File "/usr/local/src/roundup/roundup/scripts/roundup_server.py", line 275, in run_cgi
    self.inner_run_cgi()
  File "/usr/local/src/roundup/roundup/scripts/roundup_server.py", line 418, in inner_run_cgi
    self.wfile.write(data)
  File "/usr/lib/python3.9/socketserver.py", line 799, in write
    self._sock.sendall(b)
BrokenPipeError: [Errno 32] Broken pipe

There were 2 more broken pipe errors as the attempt to handle the initial exception led to more exceptions (with the same broken pipe error).

Since the server has not returned to the command prompt I guess it's still running and this is not technically a crash.  But it doesn't work.  Not a good look for a first encounter with the system.

Environment
===========

Python 3.9
Debian GNU/Linux 11
I do have a firewall running, but I don't think it covers the loopback interface.  There are various other security systems active, including AppArmor and some process isolation, I think.  Running under SystemD.
Linux barley 5.10.0-42-amd64 #1 SMP Debian 5.10.251-4 (2026-05-08) x86_64 GNU/Linux

I was running as myself, not root.