If you know of a single instance in history where electronic intrusion was cited as casus belli, feel free to mention it. Can't prove a negative, but I'm pretty confident there are no examples. Which means, by default, it's treated as espionage.
Your point is correct. The CIA/FBI/HUAC and other organizations in the USA spent the entire second half of the 20th century telling us that the USSR had inserted spies into the United States government, subversive propagandists into cinema/journalism, and violent revolutionaries into social movements. At no point did we respond to this allegedly massive, pervasive, sweeping literary, visual, analog, in-person, and electronic intrusion, as justification to unleash the ICBMs and put boots on the ground in Latvia.
We executed Julius and Ethel Rosenberg. They stole technical knowledge of electronic equipment and specific information about uranium enrichment from the Manhattan Project. These weren't random lone-wolf revolutionaries. They were literally paid agents of the government of the USSR. America didn't roll tanks and take off every zig for great justice. We killed the convicted espionage criminals and let the missiles continue sleeping in their mountain lairs.
The same was true throughout history. Spying is not some new invention of the electronic age. Royal courts and government ministers have been turned as spies to intercept secrets and disrupt the functions of the kingdom. Torture and grisly execution awaited them if caught, and they certainly would be used for stoking tribal/royalist/nationalist fervor among the population, but groups weren't going to war every time they caught spies and saboteurs. We have writings on the subject going back basically for as long as written history of civilization has existed, We don't need thousands of years of computers to set a precedent for this practice.
And even if, for some reason, the entire historical record of human civilization weren't enough for someone, we have a case study within our lifetime. The governments of USA and Israel conducted a targeted attack on computerized infrastructure in Iran. Sabers were rattled all around, imams railed, western diplomats smirked while issuing non-denial denials, American political candidates sang Beach Boys songs on campaign stops. And of course all the ops and counter-ops and double-reverse counter ops continue. But no fighter jets were deployed.