AI-Driven Refactoring in PHP: When to Trust Copilot (and When to Take the Wheel)

Legacy PHP codebases are predominantly synchronous, and refactoring them toward concurrency using Fibers with event loops like Revolt or Amp can yield significant performance gains. However, AI tools like Copilot can introduce subtle bugs such as shared state issues, false-positive tests, and happy-path bias when used without precise prompts and architectural constraints. The article advocates a 'Prompt–Refactor–Verify' cycle and constraint headers to prevent architecture drift during AI-assisted refactoring.