The agent is the identity.
A persistent agent is an identifiable member of your company with recoverable role assignments, permissions and work history. Its identity is distinct from the model providing reasoning and the process currently executing work.
Persistence means the right state can be recovered. It does not mean the agent is always running or has unrestricted authority.
The role is the job.
A role describes what the agent is responsible for. A research analyst investigates questions; an engineering agent builds and changes systems; a reviewer evaluates the result.
Start with the responsibilities your company actually needs. An unused job title is not productive capacity.
Functions turn a role into useful work.
Functions are the tasks an agent can perform within its role: compare sources, prepare a report, implement a change or check acceptance criteria. Connect each function to the tools, information and permissions it requires.
One company, with you in charge.
You set priorities and operating boundaries. Important decisions can require your review. Recorded work products and action results make oversight possible.