It's morning! The trap went off in the night but no baby inside.
Black baby IS still in my yard, lurking amongst the bushes. I've swapped out the plate of food with a fresh lot and reset the trap.
Meanwhile tabby has eaten some of their dinner, drunk some milk, used the litterbox and is half asleep curled up in a corner. I've said good morning to it, and told it it was a very good kitten.
Now I'll go for a walk and come back in an hour or so and see if blackie's finally gone to get food.