Yes Godfrey that is the direction the question is going. In a very general sense, I am trying to frame the question: If justice is something that happens by agreement, then is it going to be appropriate to call every breach of every agreement "unjust."
Maybe it is just me thinking about this for the first time, but it seems to me that it would be logical for someone to reach that conclusion if they are not careful.
As far as "social contract" theory goes it would be necessary to define what one means by that in order to make any sense of the discussion, but the basic issue is that it does not seem correct to presume that Epicurean justice is totally or even primarily a matter of contract. Because if you can walk out of the contract at any moment that you find it to be of disadvantage to you, then it hardly seems possible to call every walk-away from every contract "unjust."
And so either (1) "agreement" is not really the heart of the issue, or (2) "justice" is a word that REALLY has little meaning, compared to what "regular people" we think it does.
I am beginning to think that (2) is the real issue.