Type Design for Performance When to Use This Skill Use this skill when: - Designing new types and APIs - Reviewing code for performance issues - Choosing between class, struct, and record - Working with collections and enumerables --- Core Principles 1. Seal your types - Unless explicitly designed for inheritance 2. Prefer readonly structs - For small, immutable value types 3. Prefer static pure functions - Better performance and testability 4. Defer enumeration - Don't materialize until you need to 5. Return immutable collections - From API boundaries --- Seal Classes by Default Sealing clas…