Nothing cheers up a tech columnist more than the sight of $600bn being wiped off the market cap of an overvalued tech giant in a single day. And yet last Monday that’s what happened to Nvidia, the leading maker of electronic picks and shovels for the AI gold rush. It was the biggest one-day slump for any company in history, and it was not alone – shares of companies in semiconductor, power and infrastructure industries exposed to AI collectively shed more than $1tn in value on the same day. The proximate cause of this chaos was the news that a…