Thanks for checking things out Khen1950fx , and thanks for the link to the validator. The DTD is definitely not valid and needs to be fixed. I tried running the app with the statement commented out that stores 'messages' in the stash, and the web page renders and displays OK (minus the values from the database of course).

#$c->stash->{messages} = $c->model('TestDatabase::test');
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There must be something about the structure of 'messages' in the stash that TT doesn't like. I don't know enough about DBIx::Class (yet) to know what to look for, but I'll keep digging. Thanks again.