Is there a straight forward way to use Exceptions for 400 responses? i.e. can my handler fn throw some special "client error" type exception, and the response will be a 400, with a body I specify, and not a 500 server error?

Yes. Throw a ex-info with :status and :body in the ex-data map

Thanks @malcolmsparks. I thought I had tried that, but it might be something specific with my setup that's mangling it somewhere along the way.

Good idea to look at the code for the return interceptor.

Will do. Thanks for the help!!

@nha thanks for reporting. The last release is a work in progress - I thought I'd done rnough to release without breaking anything -