# Domain Layer
Pure Agentty-specific entities, policies, and display-neutral projections.
- Keep I/O, persistence rows, subprocesses, and terminal rendering out of this layer.
- Reuse provider models from `ag-agent` and frontend-neutral session models from
`ag-session`; do not create competing domain types.
- Update `docs/site/content/docs/agents/backends.md` for visible provider/model changes
and `docs/site/content/docs/usage/workflow.md` for session lifecycle or size changes.