What problem does it solve? It turns an approved change proposal and specs into a concrete technical design, capturing architecture decisions, data flow, file changes, and testing strategy so implementation work starts from a documented plan rather than guesswork. ## Core Features & Use Cases - Design Document Generation: Produces a structured design.md covering technical approach, architecture decisions with rationale, data flow diagrams, file change tables, interfaces, and testing strategy. - Multi-Mode Persistence: Stores the design artifact via Engram topics, OpenSpec filesystem conventions, hybrid mode, or returns it inline depending on the artifact store mode. - Threat Matrix Integration: Applies an applicability-driven threat matrix for designs touching routing, shell commands, subprocesses, VCS/PR automation, or process integration, propagating applicable rows into tasks and RED tests. - Use Case: After an orchestrator approves a change proposal, the sdd-design sub-agent reads the affected codebase, documents each architecture decision with alternatives and rationale, and hands a design summary to the sdd-tasks phase. ## Quick Start Ask the orchestrator to run the SDD design phase for your change so the sdd-design sub-agent produces a design.md from the existing proposal and specs.
