As far as I’m aware there were border skirmishes prior to China’s invasion. However, there was a context for that. The Sino-Soviet split led to China becoming very suspicious of Vietnam’s motives since they maintained good relations with the USSR. As such, China supported the Khmer Rouge in order to gain influence in the region.

I don’t have to explain why that was a huge mistake. However for context, Vietnam was forced to invade Cambodia after the Khmer Rouge crossed the border and massacred thousands of Vietnamese civilians. As a consequence Chinese leadership basically believed they had been encircled by the USSR and its allies. IIRC there was a troop buildup at the border as China tried to incite rebellion from ethnic minorities including ethnic Chinese within Vietnam. This is the context for the border skirmishes and the eventual invasion.

That is correct, there were border raids which prompted the invasion, but the Sino Soviet split is what caused the worsening relations which led to that. Basically, the invasion was cringe, even if there was some justification for it, but what was more cringe was the repudiation of Stalin and the revisionism in the USSR that followed by corn boy.

Yeah that, and to expand a little, he was often derided by hardliners for being a sellout, and the plan to develop productive forces in China had some close calls from a full capitalist restoration. It seems to have worked out so far however, since the PRC was originally an impoverished pariah state, and now it is more advanced in many respects than the west. The work that needs to be done now is to take the productive forces that the capitalists gleefully supplied in exchange for cheap labour and turn it towards domestic production and consumption.