second-brain

A second brain is a tree of subject clusters with a single entry point (index.md at the root). Clusters nest as deep as the subject needs:

$BRAIN_ROOT/index.md            ← the one entry point
  personal/index.md
    travel/index.md
      summer-2026-ukraine/index.md
        packing-list.md         ← notes live in clusters
  work/index.md