Turns a feature PRD into a technical implementation plan — system architecture across frontend/API/business-logic/data/infrastructure layers, database schema, API design, frontend component hierarchy, and security/performance considerations, carrying forward the PRD's Constraints and Business Rules as concrete technical invariants, in prose and plain-Markdown diagrams only (no Mermaid, no real code). Use when a feature PRD or spec exists and needs a technical design before task breakdown, or when asked for an "implementation plan", "technical design for this feature", or to "turn this PRD into an architecture doc".
