Charlie Stross@target Have a kernel that boots straight into a terminal running busybox.
JdeBP@cstross isn't even joking, I think.
Both BusyBox and ToyBox actually do have an init program, a getty program, and a login program.
BusyBox also has the Almquist shell. ToyBox has a Landley shell. BusyBox even has runit.
It is possible to have a system where even if you are doing various things in a shell you're just invoking the same program image over and over, using all of the same code that is there in process #1.