Event X happens. How you react depends on your state of mind.
Same problem as with coding. As soon as outputs are not wholly dependent on inputs, and they can have side-effects, all bets are off. Anything could happen.
On the per-event basis, this model boils down to a 'function' evaluating each event with multiple outputs and inputs:
Inputs: the stimuli, mental state prior to stimuli
Outputs: your actions and resultant mental state
The output mental state is then the input for the next iteration/evaluation.
Say the universe is perfectly deterministic. You could look into the future by simulating everything perfectly but why would that prohibit free will? Most people wouldn't argue that an all knowing god would mean free will is impossible, why is this different?
I'd argue that an all-knowing God is something that can't really be reasoned about. It's the introduction of an infinite value into the discussion (or maybe more like a division by zero?). You end up with logically contradictory statements when describing the properties of such a being.
Maybe the general definition of free will most people seem to go with just doesn't deal with weird edge cases because it basically developed to fit reality.