@Gertjan Klein thanks for your help and sorry for my delayed response.

I did not realize the message body is not set if there’s an error.  This explains a lot.  I was previously doing a try/catch and trying to set the %Status error text into the StringContainter response and frustrated that it wasn’t there.  I think I’m trying to overdo what Ensemble already does for free.  I also think I need to keep a response a response and keep errors as errors and not try to combine them. 

But thank you for your method here to get the header ID.  Since as you say it's not trivial, it makes me think it's unconventional and again I'm trying to use the system in ways it wasn't really designed for.  However, it's handy to understand how this works.  Thanks for helping me think through this!

Thank you!

sortbox - If present, the Search Page displays a set of radio buttons that allows the user to choose how to sort the results.

I wouldn't have immediately thought that would solve it but it makes sense along with your explanation.

Out of curiosity, how would you override that write statement in %CSP.Lookup?  Isn't that generated code which one wouldn't want to touch?