whoever is displaced by another access goes back to the login

whoever is displaced by another access goes back to the login

The farewell added a moment ago stopped the stream and showed a notice, the
same in every case. But the cases are two, and they want two different
answers.

If the two windows share the SAME session, it cannot be sent to the login:
the session cookie is shared between the tabs of the same browser, so
index.php would let it straight back in and the bouncing would start again.
It was checked that deleting the cookie from the displaced window would not
be enough either: the daemon reads the session ONLY from there (a stream with
sess in the url but no cookie is refused), so deleting it would disarm the
winning window as well, since the cookie is shared. For this case the notice
without a return to the login stays.

If instead the old stream belonged to another session - the "ghost swap" of
add_user(), that is a new access with the same name from another browser -
its session is orphaned by now and it must go back to the login: there
ghost_sess shows it "La tua sessione e' stata assegnata ad un altro browser"
and it does not come back in, because that session is no longer valid.

To tell them apart, the session the stream was opened with is recorded in
rd_sess, and when it is replaced that is compared with the one of the
newcomer.

Checked in both cases: same session -> xstm.stop() and the notice, no return
to the login; different session -> xstm.stop() and a return to index.php,
where the message really shows up. A complete game confirms it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014M1jiEq9cHdE5SE5j6vFuE