draft-plan-shells

Decompose a specification file into shell plans with YAML frontmatter. Each shell captures the wiring invariants (Produces, Consumes, Covers) and high-level Implementation Steps without committing to file paths. Use when the user asks to "draft plan shells", "create plan shells", "break spec into shells", "decompose spec into sessions", "draft shells from spec", "generate shells from spec", or "make shells from spec".