"Sure as hell I'm going to do everything in my power to kill him back" and "I must follow through on my precommitment" are the same thing. "Irrational actions" like the desire to take revenge when it doesn't help are how humans implement precommitment.

Also, I wish that anyone who used the phrase "read your source code" in reference to decision strategies, with the implication that reading your source code means he knows what you would do, had to learn about the Halting Problem.

I think this question is actually not a matter of opinion. One's answer to this question really depends on what context and communications situation you interpret the question to imply. Do you exist in a thought-experiment void or in the normal world? Are there spectators who learn from your actions? Do you have other concerns in your life that you care about? Can you negotiate with the other person more? Etc.