Gosh, that was quick! Thanks, both.
My instinct is not to tip, a lesson learned in Australia many years ago when a waitperson cheerfully explained that he didn't need my tip as he earned a decent wage.
I think it's also a cultural thing - Japan and Australia on one side, the US on the other. (Not saying either is right or wrong.) Our ex-military man in Oslo was a volunteer. I don't know about our helper at CPT, but she struggled. OTOH the buggies at LHR T5 and DOH had uniformed employees as drivers.