They should be locked up, but not for terrorism. Terrorism is about frightening people to manipulate them. This is more like state level vandalism. Also their stuff should be seized to pay for the damage.
Why not? Using violence against civilian (infrastructure) to achieve political goals.. seems to fit.
Sure you could argue violence.. my take would be if you are using an oil tanker to drag a few ton piece of metal with the intent to break stuff.. it's pretty violent.
Indeed there needs to be a show of stenght since that is what small brain bully nations understand.
There would be no constant border breaching planes if we shot down every single one. There would only be respectful and cooperative russia that doesn't start wars.