Phases 3-6 (complete proposal, drill-downs, design preview, writing
DESIGN.md) move to sections/proposal-and-preview.md, read on demand after
product context + research. Skeleton 80,719 -> 59,229 B (-27%); union
preserved. Adds the CARVE_GUARDS entry.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Garry Tan