A streaming event published when a task's status changes. Emitted during
message/stream and tasks/resubscribe.
Wire shape requires kind: "status-update", taskId, contextId,
status, final (boolean — true if this is the last event in the stream).
Summary
Types
@type t() :: %A2aEngine.Types.TaskStatusUpdateEvent{ context_id: String.t(), final: boolean(), metadata: map() | nil, status: A2aEngine.Types.TaskStatus.t(), task_id: String.t() }