that's embarrassing, thank you.
## \vec r' (t) = <-2\sin t, 2\cos t, 0> ##
## \vec F (\vec r (t)) = <-2\sin t , 2\cos t, -\cos (2\sin t)> ##
## \int_0^{2π} <-2\sin t , 2\cos t, -\cos (2\sin t)>⋅<-2\sin t, 2\cos t, 0> \, dt = \int_0^{2π} (4\sin ^2 t +4\cos ^2 t) \, dt = 4 \int_0^{2π} \, dt = 8π ##