Interface ObserverSessionMetrics

interface ObserverSessionMetrics {
    sessionId: string;
    startedAt: string;
    completedAt?: string;
    durationMs: number;
    taskCount: number;
    successCount: number;
    failureCount: number;
    tokenUsage: ObserverTokenUsage;
    costMetrics: ObserverCostMetrics;
    routingDecisions: number;
    eventsProcessed: number;
}