What problem does it solve? Effect v4 renamed and restructured many error-handling APIs from v3, and mixing up error channels, defects, and the new flattened Cause model leads to untyped failures and broken recovery logic. This Skill provides authoritative v4 guidance so typed errors are modeled, caught, and recovered correctly. ## Core Features & Use Cases - v3-to-v4 API Migration Tables: Authoritative mappings for renamed catch combinators (catchAll to catch, catchSome to catchFilter), the flattened Cause structure, and error class renames from Exception to Error suffixes. - Error Class Design Guidance: Decision trees for choosing Schema.TaggedError, Schema.Error, or Data.TaggedError, plus patterns for reason unions, HTTP status annotations, and cause wrapping conventions. - Recovery Pattern Coverage: Examples for catchTag arrays, catchTags with orElse fallbacks, catchReason/catchReasons for nested reason unions, unwrapReason, catchEager, and yieldable errors in generators. - Use Case: When migrating an Effect v3 service that uses catchAll and recursive Cause trees, apply this Skill to rewrite handlers with v4 catch, catchTag arrays, and the flat reasons array while preserving type safety. ## Quick Start Ask the assistant to refactor an Effect service's error handling to Effect v4 using Schema.TaggedError classes and catchTag recovery.
