as with all things, a “perfect” free will is not possbile. but neither is perfect enslavement. There are always precursors and predetermining factors which have to various degrees influenced a particular individual’s decision. The degree to which that individual consciously allows those factors to come into their thoughts and guide what they do seems to be a good measure of “free will”, yet, they have indeed “chosen” that very variable; that is, the degree to which each of those things influence a person, so is this any less “free”.
And by the same token, it is often in the individuals who seem least conscious of their enslavement of will that we are most likely to deem enslaved.
what i might suggest then, is that Free will exists, in some degree, the moment the idea is understood by a given individual.
It seems fair to say that strict lack of free will (as in Skinner’s Walden Two) is improbable in any long term experiment. And perfect free will as i believe tha character Castel tries to uphold is also tricky.
Overall i’d say that Conditioning of the Will is essentially inevitable but can be altered so that the individual can take a greater control of what s/he does.