Four horns! This was a fourth instar larva caught in the act of moulting into fifth. I moved so the head was against the further leaf, not the sky:
The old head is beneath, gazing down on the camera, and the new head, with soft, light-coloured horns, is above. Some shed skin is visible.
I did eventually find Agni. He entered 5th instar on 16th May, 12 days ago. The tree is dense with leaves and it will be pure luck if I can find his pupa:
Finally, a cute picture of Māyā, a fourth instar caterpillar: