057-design-feature-toggles

# Feature Toggles Design Guide Java Enterprise developers through safe feature toggle design and lifecycle management. **This is an interactive SKILL**. **What is covered in this Skill?** - Deciding when a feature toggle is appropriate versus a branch, configuration change, deployment change, or parallel change - Classifying release toggles, operational kill switches, experiment toggles, permission toggles, and migration toggles - Designing typed toggle ownership, defaults, evaluation scope, fallback behavior, observability, and rollback controls - Implementing toggles in Java services without scattering flag checks or creating hidden long-term complexity - Reviewing toggles for release, rollback, security, privacy, concurrency, and maintenance risk - Testing both enabled and disabled paths, configuration failure behavior, rollout rules, and cleanup readiness ## Constraints Use feature toggles as explicit, owned runtime control points rather than hidden conditional complexity. - **MUST** read `references/057-design-feature-toggles.md` before applying feature toggle guidance - **MUST** classify the toggle type, owner, expected lifetime, default state, rollout audience, and removal trigger before recommending implementation - **MUST** design safe defaults, fallback behavior, observability, and rollback behavior for runtime evaluation failures - **MUST** keep toggle evaluation centralized, typed, and testable instead of scattering raw configuration lookups through business...