Costco is the highest-quality compounder in consumer retail, powered by a self-reinforcing membership flywheel (92.3% U.S./Canada renewal, 40.4M Executive members driving the majority of sales) that converts a structurally low-margin merchandise model into a recurring, near-100%-margin membership-fee annuity. At roughly 42x forward FY2027E earnings the stock is priced for perpetual execution: business quality is genuine but the margin of safety is thin, and the -5% post-Q3 reaction on a broad-based beat confirms the market will not reward further execution at this multiple. For the systematic-alpha program, COST is also the single highest-value signal source in staples retail: its monthly comparable-sales disclosure is the 'TSMC monthly revenue' of retail, delivering 12 high-frequency data points a year that lead WMT quarterly prints by four to eight weeks.