SDLC 2: Design

In Phase 1 you turned messy stakeholder input into a decomposed backlog: prioritized requirements, user stories, and units with task-comments marked ACTIVE. Everything in Phase 1 was cross-unit — describing the whole project, not any one feature.

Phase 2 is where the work narrows. From here through Phase 3 you build one unit at a time. The first per-unit artifact is the feature spec: a precise contract for what the ACTIVE unit must do. Once the spec is validated, you explore the codebase, design an architecture to host the feature, capture decisions, and pass a design review gate.

By the end of this phase, the ACTIVE unit is fully specified and fully designed — ready for tests and code in Phase 3.

• Write a feature spec for the ACTIVE unit and validate it against five quality dimensions
• Package the validation prompt as a reusable /validate-spec skill
• Explore a codebase and generate an architecture plan with trade-off analysis
• Document architecture decisions in ADRs
• Update CLAUDE.md as a minimal project pointer file
• Run a design review gate before implementation

Phase 1 produced a backlog with task-comments marked ACTIVE. Now you need to turn that one backlog entry into a precise, per-unit contract. You write the feature spec, validate it, then explore the existing Express codebase — its routes, data layer, middleware patterns, and conventions. Armed with both the spec and the codebase context, you propose an architecture plan with trade-offs, capture decisions in an ADR, update CLAUDE.md, and pass a design review gate before implementation begins.

Phase 3 reads the spec, architecture plan, and acceptance criteria to generate tests and implement.