regressionlisted

# Regression Patterns Domain expertise for detecting functionality regressions and validating implementation intent. Use alongside `devflow:review-methodology` for complete regression reviews. ## Iron Law > **WHAT WORKED BEFORE MUST WORK AFTER** > > Every change carries regression risk. Removed exports break consumers. Changed signatures > break callers. Modified behavior breaks expectations. The burden of proof is on the change: > demonstrate no regression, or document the intentional breaking change. --- ## Regression Categories ### 1. Lost Functionality Features, exports, or capabilities that existed before but are missing after. | Type | Risk | Detection | |------|------|-----------| | Removed exports | Breaks consumers | Compare `export` statements | | Removed CLI options | Breaks scripts | Compare option definitions | | Removed API endpoints | Breaks clients | Compare route handlers | | Removed event handlers | Breaks integrations | Compare `.on()` calls | ```typescript // VIOLATION: Export removed without deprecation // BEFORE: export function deleteUser(id: string): void { } // AFTER: (removed) - consumers will break! ``` ### 2. Broken Behavior Code still exists but behaves differently in breaking ways. | Type | Risk | Detection | |------|------|-----------| | Changed return types | Null dereference | Compare function signatures | | Changed defaults | Unexpected behavior | Compare default values | | Removed side effects | Missing events/logs | Compare emit