Base coordination type for verifiable actor attribution. An Actor describes the accountable entity on whose authority a timeline entry, operation request, response, status change, customer action, or other coordination event was produced. The actor may be a human principal, an organization, an automated service, an AI agent, a device, or a provider-defined specialization, but the crucial semantic point is that the event source is making an attribution claim that downstream documents can inspect. Actor attribution is not permission by itself. It is evidence about who or what caused an action. A Timeline Provider or other event source authenticates the party trying to append an entry to a timeline and records the actor category and any provider-specific audit fields. Blue documents then decide, through Actor Policy, operation-specific rules, or domain-specific logic, whether that actor is allowed to perform the requested operation. Processors MUST NOT infer actor category from message text; they use the explicit actor node supplied with the event or timeline entry. Concrete actor types should precisely state what the provider is asserting. Principal Actor means the action is attributed directly to the principal or account owner. Agent Actor means the action is attributed to delegated automation acting on behalf of a principal. Provider-specific actor types may describe UI authentication strength, API credentials, agent sessions, delegation references, device identity, assurance level, or other auditable evidence. Because the description of an actor type is identity-bearing Blue content, it should be written as the normative semantic contract of that actor type, not as informal documentation.