feat(events): isOnline presence check for a user and app

src/backend/services/events/EventForwardService.ts

@@ -403,6 +403,17 @@ export class EventForwardService extends PuterService {
         }
     }
 
+    /**
+     * Whether the pair holds a socket anywhere: this node, this region or a
+     * peer region. Only this node's sockets count where presence is not kept.
+     */
+    async isOnline(userId: number, appUid: string | null): Promise<boolean> {
+        if (this.services.socket.has(forwardTarget(userId, appUid))) return true;
+        if (!this.active) return false;
+        if (await this.heldInRegion(userId, appUid)) return true;
+        return (await this.regionsFor(userId, appUid)).length > 0;
+    }
+
     /** Send one `single` to a named region, carrying what settles it. */
     handOff(region: string, delivery: ForwardableDelivery): void {
         this.#send(region, delivery);

src/backend/services/events/forwarding.test.ts

@@ -1647,6 +1647,21 @@ describe('presence moving in another region', () => {
     });
 });
 
+describe('isOnline', () => {
+    it('is true for a socket on this node, in this region or in a peer region', async () => {
+        const west = makeRegion('west', ['east']);
+        const east = makeRegion('east', ['west']);
+        await register(west);
+        expect(await west.forward.isOnline(userId, null)).toBe(false);
+
+        east.rooms.add(String(userId));
+        await east.forward.noteConnect(actorFor(), 'tab-1');
+        expect(await east.forward.isOnline(userId, null)).toBe(true);
+        expect(await west.forward.isOnline(userId, null)).toBe(true);
+        expect(await west.forward.isOnline(userId, 'app-other')).toBe(false);
+    });
+});
+
 // -- Decommissioned regions --------------------------------------------
 
 describe('a row naming a region that is not a peer', () => {