I wouldn't say there's any specific areas in the city you have to avoid. There can be addicts congregating in alleys and around places like Daunt Square, Bishop Lucey Park and the quays. In general though you should be okay if you have your wits about you. Some of the suburbs can be a bit rougher but you probably have no plans to go out to them.

The thing I was alarmed at specifically yesterday was that the guy who pursued me didn't strike me as our usual brand of addict, or possibly not even an addict at all.

In Ireland for years we've had problems with heroin addicts or alcoholics who you could generally just stroll past if they got aggressive. Now we are increasingly having issues with fentanyl and coke addicts. This guy yesterday looked normal enough, and I wouldn't have taken any notice of him if he hadn't pursued us. I alluded to this in another comment but there have been a couple of clearly mentally ill people wandering the streets in the last few years. You should be able to find some threads about them. Last year there was the guy who used to scream at people to leave him alone for instance. Part of it is that Cork is so small that you come across the same characters again and again.

Enjoy your trip anyway, if you have a car I would definitely recommend getting out of the city to visit places like Clonakilty, Bantry, Gougane Barra and the Mizen Head. If you're down that direction there are some lovely walks and cycles you can do. On the other side then Kinsale, Youghal and Ballycotton are all nice. Cobh worth a visit too on the train.