Regression Fear in AI-Generated Codebases — Why Every PR Feels Like a Gamble

"Every PR is a gamble. We just don't know what it'll break." If your team has stopped merging on Fridays — or Thursdays — you're experiencing regression fear. Not a psychological problem. A structural one. This post explains the mechanism, how to measure it, and the fix. The Mechanism: Unbounded Blast Radius In a well-structured codebase, a change in module A affects module A and its direct dependents. The blast radius is bounded and predictable. In most AI-generated codebases past month 3, the blast radius is unbounded: BLAST RADIUS MAP Change: update pricing display PREDICTED impact: ACTUAL impact: pricing/ui.tsx pricing/ui.tsx payments/checkout.ts users/dashboard.tsx notifications/email.ts predicted: 1 file actual: 4 files blast radius: unbounded The mechanism: AI generates code that works by taking the shortest path. That shortest path often creates implicit dependencies — shared state, cross-module imports, business logic in unexpected places. Each implicit dependency extends the