Reduce redundant runtime updates

packages/app/src/hooks/use-client-activity.test.tsx

@@ -49,7 +49,10 @@ vi.mock("@server/client/daemon-client", () => ({}));
 function createTestClient() {
   return {
     isConnected: true,
-    subscribeConnectionStatus: vi.fn(() => vi.fn()),
+    subscribeConnectionStatus: vi.fn((listener: (state: { status: "connected" }) => void) => {
+      listener({ status: "connected" });
+      return vi.fn();
+    }),
     sendHeartbeat: vi.fn<(payload: HeartbeatPayload) => void>(),
   };
 }
@@ -68,13 +71,15 @@ function heartbeatTimeMs(client: ReturnType<typeof createTestClient>): number {
 
 async function renderActivityHook({
   client = createTestClient(),
+  focusedAgentId = "agent-1",
 }: {
   client?: ReturnType<typeof createTestClient>;
+  focusedAgentId?: string | null;
 } = {}) {
-  function Probe() {
+  function Probe({ focusedAgentId }: { focusedAgentId: string | null }) {
     useClientActivity({
       client: client as unknown as Parameters<typeof useClientActivity>[0]["client"],
-      focusedAgentId: "agent-1",
+      focusedAgentId,
     });
     return null;
   }
@@ -84,10 +89,16 @@ async function renderActivityHook({
   const root = createRoot(container);
 
   await act(async () => {
-    root.render(<Probe />);
+    root.render(<Probe focusedAgentId={focusedAgentId} />);
   });
 
-  return { client, root };
+  const rerender = async (nextFocusedAgentId: string | null) => {
+    await act(async () => {
+      root.render(<Probe focusedAgentId={nextFocusedAgentId} />);
+    });
+  };
+
+  return { client, rerender, root };
 }
 
 async function advance(ms: number) {
@@ -138,6 +149,24 @@ describe("useClientActivity", () => {
     expect(getDesktopSystemIdleTimeMs).not.toHaveBeenCalled();
   });
 
+  it("sends one immediate heartbeat when the focused agent changes", async () => {
+    const rendered = await renderActivityHook();
+    root = rendered.root;
+
+    expect(rendered.client.sendHeartbeat).toHaveBeenCalledTimes(1);
+    rendered.client.sendHeartbeat.mockClear();
+
+    vi.setSystemTime(new Date("2026-04-19T10:00:05.000Z"));
+    await rendered.rerender("agent-2");
+
+    expect(rendered.client.subscribeConnectionStatus).toHaveBeenCalledTimes(1);
+    expect(rendered.client.sendHeartbeat).toHaveBeenCalledTimes(1);
+    expect(latestHeartbeat(rendered.client)).toMatchObject({
+      focusedAgentId: "agent-2",
+      lastActivityAt: "2026-04-19T10:00:05.000Z",
+    });
+  });
+
   it("drives lastActivityAt forward from Electron idle polling", async () => {
     platformState.isElectron = true;
     getDesktopSystemIdleTimeMs.mockResolvedValue(0);

packages/app/src/hooks/use-client-activity.ts

@@ -3,6 +3,7 @@ import { AppState } from "react-native";
 import type { DaemonClient } from "@server/client/daemon-client";
 import { getIsElectron, isWeb, isNative } from "@/constants/platform";
 import { getDesktopSystemIdleTimeMs } from "@/desktop/electron/idle";
+import { useStableEvent } from "@/hooks/use-stable-event";
 
 const HEARTBEAT_INTERVAL_MS = 15_000;
 const ACTIVITY_HEARTBEAT_THROTTLE_MS = 5_000;
@@ -41,7 +42,7 @@ export function useClientActivity({
     lastActivityAtRef.current = new Date();
   }, []);
 
-  const sendHeartbeat = useCallback(() => {
+  const sendHeartbeat = useStableEvent(() => {
     if (!client.isConnected) return;
     client.sendHeartbeat({
       deviceType,
@@ -50,7 +51,7 @@ export function useClientActivity({
       appVisible: appVisibleRef.current,
       appVisibilityChangedAt: appVisibilityChangedAtRef.current.toISOString(),
     });
-  }, [client, deviceType, focusedAgentId]);
+  });
 
   const setAppVisible = useCallback(
     (nextVisible: boolean) => {
@@ -191,10 +192,6 @@ export function useClientActivity({
       }
     });
 
-    if (client.isConnected) {
-      startHeartbeat();
-    }
-
     return () => {
       unsubscribe();
       stopHeartbeat();