The online trading app Robinhood became a cultural phenomenon and a Silicon Valley darling with a promise to wrest the stock market away from Wall Street’s traditional gatekeepers and “let the people trade” — making it as easy to put millions of dollars at risk as it is to summon an Uber.This past week, in the middle of a market frenzy pitting amateur traders against hedge fund bigwigs, that veneer began to chip. As it turned out, Robinhood was at the mercy of the very industry it had vowed to upend.The frenzy morphed into a crisis when legions …
