Agent Skills: existing-code-first

Use for any coding implementation, bug fix, refactor, test addition, code review, or agent handoff where new code may be added or existing behavior may be changed. Before creating new functions, classes, files, utilities, services, hooks, components, schemas, constants, validators, test helpers, or dependencies, search existing code for equivalent or similar responsibilities and prefer reuse, extension, relocation, or consolidation over parallel reimplementation.