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You need to combine the circle and line plots prior to doing the animation.

p = circle((0,0), 0.8, fill=true, color='magenta',xmin=-1,xmax=1,ymin=-1,ymax=1)
a = animate((p+line([(0,0), (cos(c), sin(c))],thickness=3) for c in srange(0,2*pi, pi/4)))