I did do that, and my code resumed working. That's what made me realize
that it was likely that it had something to do with Sitemesh rather than
other parts of the project.
What I eventually figured out was that the break happened when I renamed a
menu.jsp file included with <jsp:include> to menu.jspf. This file was
included within the Sitemesh decorator. After I changed it to .jspf, it
stopped working, throwing no exceptions, returning only a blank web page.
I renamed it back to .jsp and it started working again.
I think I would understand why this is if I were to understand the
processing order of .jsp includes and Sitemesh decorators better. (I bet
you know!) But for now, I've advised my team not to use .jspf file
extension on our new projects which use Sitemesh.