i remember the first time I got a building violation from the city, it scared the crap out of me. Number one rule: don't panic.
You likely are responsible because the city doesn't care who did the work, only who owns it, however they are actually pretty fair and level headed particularly when dealing with owner occupied properties.
That said you should bring a lawyer to court when you go, I can give you a recommendation. Best case scenario: the city wants you to address a more minor violation and they call out the addition as a way to get your attention and gain leverage to get the smaller violations fixed. Worst case scenario: you will have to get an architect to submit plans and ensure it is to code. But if it's bad enough that they want you to do that, then it is probably something you should be doing anyhow as the city doesn't just go around looking for violations to stick owners on.
Oh and one otherthing, just make sure you cooperate with the city employees as best you can. A little bit of honey when dealing with the people who represent our lovely faceless beaucracy goes a looking ways in determining how hard the city is going to pursue these issues.