AI agents need structured data, not similarity search. Graph DBs are expensive, vector stores are fuzzy.Lithium is a storage engine on PostgreSQL ltree. Hierarchical, versioned, scoped queries. Two commands:npx @lithium-ai/kit init claude mcp add lithium -- npx @lithium-ai/kit serveYour agents get tools to navigate, store, and retrieve structured data on your existing Postgres.Open source, MIT.