[Catalyst] Handling expired sessions gracefully

[Steve]

I've looked in the archives and tutorials but can't seem to find 
examples of handling expired sessions gracefully.  I'm admittedly weak 
in the area of error checking, but I'm working on it :)  Here are my 
questions:
In what controller (Root.pm or MyApp.pm) and action should I check for 
an expired session?  Should I check $c->user_exists or 
$c->session_expired (not sure if I have the correct accessor)?  Once 
detected, do I forward, redirect, etc.?
TIA - Steve