It was a nymph of a Red-headed Bush Cricket (Phyllopalpus pulchellus), also known as the Handsome Trig (on the account of being both handsome and a member of the subfamily Trigonidiinae.) This species can be easily identified by the large, paddle-like mandibular palps, which these insects move in a fashion very similar to the way jumping spiders move their palps, and I wonder if their function might be spider mimicry.
The adults of this species are still a few weeks away, and they are even prettier than this immature individual, with black body and a crimson red head. I definitely will be on the lookout for them in August.
Update: I found an adult Red-headed Bush Cricket exactly one month later; read about it here.