Daycare

Daycare: two cogs in a walled yard. The CHILD wants one of two fruits -- apple or banana -- and can never reach the tall trees; the PARENT can reach everything and is paid only when the child eats, tripled when the meal is the fruit the child secretly prefers. There is no way to talk: no message channel exists in either direction, so the parent has to read the child's preference out of where it walks, what it reaches for, and what it refuses to eat. Both seats score the same number, so the pair either reads each other or both go hungry. A policy is just a prompt.