On September 17, the Federal Reserve finally cut interest rates. For Robinhood Markets, the decision was more than macro theater. Lower rates can mean two things at once: reduced income from idle cash, but a jolt of activity from retail traders chasing volatility. For a firm that still earns handsomely from order flow and option contracts, the second effect matters more in the short run.The stock has been quick to price that in. Robinhood now trades around $136.72, giving it a market value of $82.6 billion ...