Naive antiservo tab question

IIUC an antiservo tab works by deflecting a control
surface in one direction so that the control surface
then exerts a torque in the opposite direction.

For example, suppose you have an airplane that tends
to yaw to the right with the rudder and ailerons in
their neutral positions. An antiservo tab would
be adjusted to extend into the airstream to the
right so that it deflects the rudder to the left.
The airstream passing over the rudder then exerts
a left torque on the aircraft so that the aircraft
flies straight.

ISTM that when the antiservo tab is extended the
resulting torque pushes the rudder over until the
airstream over the rudder exerts a torque of
equal magnitude but in the opposite direction
so that the net torque on the rudder and antiservotab
as an assembly is zero. If that net torque is zero
how does this arrangement exert a nonzero torque on
the airplane?

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FF