Rails' Four-Layer Contract: Why Every Feature Needs a Route, Policy, Controller, AND Model Method

Every user action in a Rails app must pass through four layers — Route, Policy, Controller, and Model — and missing any one causes silent or invisible failures. The article details how each layer fails differently: routes cause NoMethodError or silently trigger wrong actions, policies return 500s instead of 403s or apply wrong authorization logic, and incomplete controller/model methods lead to data corruption without errors. A checklist approach ensures all four layers are implemented together for every new feature.