«فَأَنْتَ حُرٌّ»
Then you are free.
A nominal clause does not itself have a past or imperfect tense, but as a conditional response it may describe a state that takes effect upon future fulfillment of the condition. It should not be treated as an unconditional current assertion.
Likewise, the condition may use a past verb while the response is nominal. Interpreted as a construction, they exhibit futurity from the conditional relation as a whole, not solely from the morphology of one word.