The most important market signal this week was not that oil fell, semiconductors corrected, Micron beat expectations, or bond markets again pushed back against the idea of easy monetary policy. It was that markets are beginning to move from narrative to discipline.

For most of the past two years, the artificial intelligence trade has been driven by belief. Investors believed AI would transform productivity. They believed hyperscalers would keep spending. They believed semiconductors would remain scarce. They believed capital markets would contin...