Adopt and maintain message consumer

Alas we no longer have Oleksii nor protégé Rohit who learned a good bit about message consumer when he and Cursor deepcloned it to become Flink statement viewer.

Perform similar transformations to make a 'real class' out of the manager, then get some tests written over it; learning as we go!

Then we'll be in much better shape to augment its capabilities --- is our most used feature!