feat: add agent response scheduler

apps/freya-backend/src/notification/notification-central.ts

@@ -0,0 +1,36 @@
+import type { AgentEvent } from "@freya/agent-protocol"
+
+export interface AgentNotification {
+	kind: "agent"
+	payload: AgentEvent
+}
+
+export type NotificationPayload = AgentNotification
+export type NotificationListener = (notification: NotificationPayload) => Promise<void>
+
+export class NotificationCentral {
+	private listeners: Map<string, Set<NotificationListener>> = new Map()
+
+	registerListenerForUser(userId: string, listener: NotificationListener): () => void {
+		let listeners = this.listeners.get(userId)
+		if (!listeners) {
+			listeners = new Set()
+			this.listeners.set(userId, listeners)
+		}
+
+		listeners.add(listener)
+		return () => {
+			listeners.delete(listener)
+			if (listeners.size === 0) {
+				this.listeners.delete(userId)
+			}
+		}
+	}
+
+	async notifyUser(userId: string, notification: NotificationPayload): Promise<void> {
+		const listeners = this.listeners.get(userId)
+		if (!listeners) return
+
+		await Promise.allSettled(Array.from(listeners).map((listener) => listener(notification)))
+	}
+}