fix: pause hidden session catalog polling

ui/src/components/app-sidebar-session-data.ts

@@ -175,12 +175,11 @@ export abstract class AppSidebarSessionDataElement extends AppSidebarBase {
 
   override updated() {
     this.syncSessionsScrollObserver();
-    const snapshot = this.context?.gateway.snapshot;
     if (this.context) {
       this.synchronizeSessionCatalogAgent(this.expandedAgentId());
     }
     if (
-      !sessionCatalogListClient(snapshot, this.connected) ||
+      !this.visibleSessionCatalogClient() ||
       this.sessionCatalogLive.timer ||
       this.sessionCatalogLive.requestGeneration === this.sessionCatalogGeneration
     ) {
@@ -189,6 +188,13 @@ export abstract class AppSidebarSessionDataElement extends AppSidebarBase {
     void this.refreshSessionCatalogs();
   }
 
+  private visibleSessionCatalogClient(): GatewayBrowserClient | null {
+    if (document.visibilityState === "hidden") {
+      return null;
+    }
+    return sessionCatalogListClient(this.context?.gateway.snapshot, this.connected);
+  }
+
   private synchronizeSessionCatalogAgent(agentId: string) {
     if (agentId === this.sessionCatalogAgentId) {
       return;
@@ -265,7 +271,9 @@ export abstract class AppSidebarSessionDataElement extends AppSidebarBase {
   }
 
   private async refreshSessionCatalogs() {
-    const client = sessionCatalogListClient(this.context?.gateway.snapshot, this.connected);
+    // Hidden pages resume through the coalesced activation handler. Starting
+    // here without a timer makes catalog state updates poll at request latency.
+    const client = this.visibleSessionCatalogClient();
     if (!client) {
       return;
     }

ui/src/test-helpers/app-sidebar-cases/catalog-live-events.ts

@@ -1,7 +1,14 @@
 import { describe, expect, it, vi } from "vitest";
+import type { SessionsCatalogListResult } from "../../../../packages/gateway-protocol/src/index.ts";
 import type { GatewayBrowserClient } from "../../api/gateway.ts";
 import type { ApplicationGatewaySnapshot } from "../../app/context.ts";
-import { catalogPage, createGatewayHarness, createSessions, mountSidebar } from "../app-sidebar.ts";
+import {
+  catalogPage,
+  createGatewayHarness,
+  createSessions,
+  deferred,
+  mountSidebar,
+} from "../app-sidebar.ts";
 import "../../components/app-sidebar.ts";
 
 describe("AppSidebar session catalog pagination", () => {
@@ -44,6 +51,56 @@ describe("AppSidebar session catalog pagination", () => {
     }
   });
 
+  it("stays paused when an in-flight catalog refresh finishes in a hidden tab", async () => {
+    vi.useFakeTimers();
+    let visibility: DocumentVisibilityState = "visible";
+    const visibilitySpy = vi
+      .spyOn(document, "visibilityState", "get")
+      .mockImplementation(() => visibility);
+    try {
+      const pending = deferred<SessionsCatalogListResult>();
+      const request = vi
+        .fn()
+        .mockReturnValueOnce(pending.promise)
+        .mockResolvedValue(catalogPage([]));
+      const gateway = createGatewayHarness({ request } as unknown as GatewayBrowserClient);
+      gateway.publish({
+        hello: {
+          features: { methods: ["sessions.catalog.list"] },
+        } as ApplicationGatewaySnapshot["hello"],
+      });
+      const { sidebar } = await mountSidebar(
+        gateway.gateway,
+        createSessions("main", ["agent:main:main"]),
+      );
+      sidebar.connected = true;
+      await sidebar.updateComplete;
+      await vi.advanceTimersByTimeAsync(0);
+      expect(request).toHaveBeenCalledTimes(1);
+
+      visibility = "hidden";
+      document.dispatchEvent(new Event("visibilitychange"));
+      pending.resolve(catalogPage([]));
+      await vi.advanceTimersByTimeAsync(0);
+      await sidebar.updateComplete;
+      await vi.advanceTimersByTimeAsync(60_000);
+      expect(request).toHaveBeenCalledTimes(1);
+
+      visibility = "visible";
+      document.dispatchEvent(new Event("visibilitychange"));
+      globalThis.dispatchEvent(new Event("focus"));
+      await vi.advanceTimersByTimeAsync(49);
+      expect(request).toHaveBeenCalledTimes(1);
+      await vi.advanceTimersByTimeAsync(1);
+      expect(request).toHaveBeenCalledTimes(2);
+      await vi.advanceTimersByTimeAsync(0);
+      expect(request).toHaveBeenCalledTimes(2);
+    } finally {
+      visibilitySpy.mockRestore();
+      vi.useRealTimers();
+    }
+  });
+
   it("does not poll an older Gateway that does not advertise session catalogs", async () => {
     vi.useFakeTimers();
     try {