Function appendDagNode

Returns {
    calleeAgentId: string;
    callerAgentId: string;
    contextHash: string;
    dagId: string;
    endTs: number | null;
    eventType:
        | "agent_handoff_sent"
        | "agent_handoff_received"
        | "agent_delegation_started"
        | "agent_delegation_completed";
    nodeHash: string;
    nodeId: string;
    outcome: string
    | null;
    parentNodeId: string | null;
    prevHash: string;
    signature: string;
    startTs: number;
    taskDescription: string;
}