What a good agent schema reveals

A well-designed agent data model, read on its own, tells you what the product does: artifacts are versioned and audited (there's a versions table with a source enum); work is shareable (explicit share fields); conversations are rich event logs (JSON content, not text); async work has status fields; usage is metered; external calls are cached. The schema is the product, expressed in tables, so design it as deliberately as you design the agent loop.