engineering-design

Turn a product contract or architecture-changing request into a minimal system contract by modeling required responsibilities, state ownership, boundaries and contracts, critical runtime flows, quality guarantees, and consequential architectural decisions before implementation. Use for greenfield system architecture, non-trivial feature architecture, cross-module refactors, storage or data-ownership changes, protocol changes, concurrency or consistency changes, external integrations, and production-sensitive system changes. Read .agents/product.md and the existing codebase when present. Do not design function-level code or implementation details; hand those to design-thinking. Record ADRs only for consequential decisions with real alternatives or significant long-term consequences.