proofable_context, or the dedicated spend account if you created one.
linked: true means the agent is on your profile. A signed-in-profile agent needs verified identity. A separate spend account also needs signed limits. If a required step is missing, you get link_required, missingVerifiers, and a hosted URL for only that step.
agentId is optional only when the account identifies one agent unambiguously. Pass it whenever one account hosts several agents. Optional principal hints the owner account (not the agent account). Agent concepts
When you need to create or import first, see Agent create.