Code quality diagnosis using principles from six classic software engineering books (The Mythical Man-Month, Clean Code, A Philosophy of Software Design, Working Effectively with Legacy Code, xUnit Test Patterns, The Art of Unit Testing). Surfaces decay risks across four review modes: PR Review, Architecture Audit, Tech Debt Assessment, and Test Quality Review. Every finding follows the Iron Law: Symptom → Source → Consequence → Remedy — grounding each issue in a named principle from the books.