Thanks for your suggestion! I doubt that it's L. salicariae (a bit too big, not particularly damp enviro and no Lysimachia noticed) but that option brought me to this forum post where L. salicariae is corrected to Aphthona cyparissiae. That seems a better match, at least the genus: cyparissiae is supposed to be 'light brown' but my specimen was orange/gold/yellow. Maybe a different species, maybe just colour variation?
I read that Apthona are called 'flea beetles' because of their hind legs, and that makes sense: with the bug gone and looking at the photo, for a moment I did think that it looked confusingly flea-like.