In 2009, LinkedIn’s new engineering chief, David Henke, assembled his full crew of coders and managers for the first time and fired off tough questions. “What the heck is wrong with all of you?” was the sanitized gist of it. The fast-growing professional social network had about 50 million users, but every Thursday afternoon it went completely offline as engineers launched new features and fixed bugs. Job seekers couldn’t browse openings. Recruiters paying to trawl the website for candidates were forced to twiddle their thumbs. Clicking…