feat(gateway): add sender presence tracking

src/gateway/handlers/system.ts

@@ -11,6 +11,16 @@ export interface TokenUsageEntry {
   total: { inputTokens: number; outputTokens: number; calls: number; estimatedCost: number };
 }
 
+export interface PresenceEntry {
+  channel: string;
+  senderId: string;
+  senderName?: string;
+  firstSeenAt: number;
+  lastSeenAt: number;
+  messageCount: number;
+  status: 'online' | 'offline';
+}
+
 export interface SystemHandlerDeps {
   startTime: number;
   version: string;
@@ -31,6 +41,8 @@ export interface SystemHandlerDeps {
   getActiveRequests?: () => ActiveRequestInfo[];
   /** Optional callback to retrieve all services (channels + automation). */
   getServices?: () => ServiceInfo[];
+  /** Optional callback to retrieve tracked sender presence. */
+  getPresence?: (opts?: { channel?: string; status?: 'online' | 'offline'; limit?: number }) => PresenceEntry[];
 }
 
 export function createSystemHandlers(deps: SystemHandlerDeps) {
@@ -78,6 +90,28 @@ export function createSystemHandlers(deps: SystemHandlerDeps) {
       return makeResponse(request.id, { services: deps.getServices() });
     },
 
+    'system.presence': async (request: GatewayRequest): Promise<OutboundMessage> => {
+      if (!deps.getPresence) {
+        return makeResponse(request.id, { presence: [], summary: { total: 0, online: 0, offline: 0 } });
+      }
+
+      const params = request.params as { channel?: string; status?: 'online' | 'offline'; limit?: number } | undefined;
+      const presence = deps.getPresence({
+        channel: params?.channel,
+        status: params?.status,
+        limit: params?.limit,
+      });
+      const online = presence.filter((entry) => entry.status === 'online').length;
+      return makeResponse(request.id, {
+        presence,
+        summary: {
+          total: presence.length,
+          online,
+          offline: presence.length - online,
+        },
+      });
+    },
+
     'system.usage': async (request: GatewayRequest): Promise<OutboundMessage> => {
       const uptime = Math.floor((Date.now() - deps.startTime) / 1000);
       const usage = deps.getUsage?.() ?? { totalSessions: 0, activeConnections: 0 };