What problem does it solve? When a code change touches a module's interface, invariants, seam placement, adapters, dependency direction, or test surface, teams often add shallow abstractions or speculative indirection. This Skill applies deep-module design vocabulary to evaluate such changes and returns a structured Design Delta for the parent approval workflow. ## Core Features & Use Cases - Deep-module evaluation: Identifies callers, states the smallest honest interface with invariants and error modes, and places seams only where behavior genuinely varies. - Dependency categorization: Classifies dependencies as in-process, local-substitutable, remote-but-owned, or true external, with matching adapter and testing strategies via DEEPENING.md. - Design It Twice pattern: Generates and compares at least three distinct interface alternatives when a candidate genuinely needs them, per DESIGN-IT-TWICE.md. - Use Case: While refactoring a service that calls a third-party API, use this Skill to decide whether a port and adapter are justified, define the interface contract, and produce a Design Delta the parent gate can approve. ## Quick Start Ask the AI to apply the codebase-design skill to evaluate the module interface and seam placement for your proposed change and return a Design Delta.
