Subsystem Design Spec

A Subsystem Design Spec is the bridge between a high-level System Spec and OpenSpec's change workflow. It takes one subsystem from the system-level architecture and produces a comprehensive, implementation-ready specification with opinionated progressive phases.

Core principle: Define contracts and phases before any code exists. Each phase is independently testable, contract-bounded, and follows FP progression: types -> pure functions -> effects -> composition.

When to Use

• A System Spec (high-level) exists with subsystems identified
• You're ready to deep-dive on one subsystem before starting OpenSpec
• You're creating the second+ subsystem spec and need convention consistency