Amazing, my caterpillar may have a name after all. Your suggestion makes a lot of sense to me after looking at the Acronicta clarescens caterpillar in Wagner's The Caterpillars of Eastern North America and at the BugGuide image here. Even though the colors don't match (presumably younger individuals?), I am persuaded by the warts and the stubby "tail". Thank you!

Maybe it was not that sick after all - who knows. Anyway, I have looked at the litter again and, lo and behold, discovered an empty pupa skin in a small chunk of apparently glued-together debris. It was quite small, though. If a moth actually emerged, it must have done so after I had decided that there was no pupa. I should have known better but for now, regrettably, the caterpillar will remain a mystery caterpillar. A missed opportunity, but its way of pupating may narrow the ID possibilities