Urs, David, Simon: many thanks. I think I can see a way ahead for new scores. (Migrating old scores will require some editing to change \end from a postfix operator to a prefix operator.)
You've given me another insight into lilypond's internals. The learning process is a bit discombobulating: perhaps "internals" is the right word; it feels a bit like the old description of learning surgery ("see one, do one, teach one."). It's time for me to scrub up and put on a sterile gown...