Agent Skills: doc-coauthoring

문서 작성, 문서화, 문서, 스펙 작성, 기술 문서, 제안서, RFC, 설계 문서, 의사결정 문서 - Collaborative document co-authoring through 3 stages: context gathering, iterative refinement, and reader testing. Use when writing docs, proposals, tech specs, decision docs, or RFCs. Do NOT use for PRD/product requirements (use prd-strategist) or implementation plans (use writing-plans).