fix(server,app,desktop): route in-app notifications by presence cascade

Replaces the per-client stale/visibility policy with one shared
presence cascade so a backgrounded Firefox tab can no longer steal
in-app notifications from an active Electron desktop window.

Server (`agent-attention-policy.ts`): exports `PRESENCE_THRESHOLD_MS`
(3 min) and `computeNotificationPlan({ allStates, agentId, reason,
nowMs })` returning `{ inAppRecipientIndex, shouldPush }`. Cascade:
focus suppression requires presence; otherwise the most-recent
present client wins (lower-index tiebreak); push fires only when no
client is present, and never on `error`. `broadcastAgentAttention`
calls the policy once per event.

Electron (`daemon-manager.ts`, `idle.ts`): registers
`desktop_get_system_idle_time` returning `powerMonitor
.getSystemIdleTime() * 1000`. Renderer wrapper
`getDesktopSystemIdleTimeMs()` is best-effort: rejected IPC, null,
NaN, Infinity, or negative values return null without throwing.

Hook (`use-client-activity.ts`): Electron-only effect polls every 5s
and updates `lastActivityAtRef` only forward, so OS-wide activity
keeps a backgrounded Electron window present while in-window events
still update immediately.

`ClientHeartbeatMessageSchema` is unchanged; old/new clients and
daemons remain wire-compatible.

Tests: 52 focused tests across policy unit, dispatch, e2e, hook,
desktop wrapper, and permissions. Phase-3 dispatch test +
Phase-5 stale-poll test verified by mutation (breaking the focus
check / the `>` guard makes the exact regression fail).

packages/app/src/desktop/electron/idle.test.ts

@@ -0,0 +1,80 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+const { invokeDesktopCommandMock } = vi.hoisted(() => ({
+  invokeDesktopCommandMock: vi.fn<() => Promise<unknown>>(async () => 12_000),
+}));
+
+vi.mock("@/desktop/electron/invoke", () => ({
+  invokeDesktopCommand: invokeDesktopCommandMock,
+}));
+
+import { getDesktopSystemIdleTimeMs } from "./idle";
+
+describe("getDesktopSystemIdleTimeMs", () => {
+  afterEach(() => {
+    invokeDesktopCommandMock.mockReset();
+    vi.restoreAllMocks();
+  });
+
+  it("invokes the desktop idle command and returns the millisecond value", async () => {
+    invokeDesktopCommandMock.mockResolvedValueOnce(4_200);
+
+    const idleTimeMs = await getDesktopSystemIdleTimeMs();
+
+    expect(invokeDesktopCommandMock).toHaveBeenCalledWith("desktop_get_system_idle_time");
+    expect(idleTimeMs).toBe(4_200);
+  });
+
+  it("returns null and logs once when IPC rejects", async () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const error = new Error("ipc failed");
+    invokeDesktopCommandMock.mockRejectedValueOnce(error);
+
+    const idleTimeMs = await getDesktopSystemIdleTimeMs();
+
+    expect(idleTimeMs).toBeNull();
+    expect(warn).toHaveBeenCalledTimes(1);
+    expect(warn).toHaveBeenCalledWith("[DesktopIdle] Failed to read system idle time", error);
+  });
+
+  it("returns null and logs once when IPC returns null", async () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    invokeDesktopCommandMock.mockResolvedValueOnce(null);
+
+    const idleTimeMs = await getDesktopSystemIdleTimeMs();
+
+    expect(idleTimeMs).toBeNull();
+    expect(warn).toHaveBeenCalledTimes(1);
+    expect(warn).toHaveBeenCalledWith("[DesktopIdle] Invalid system idle time", null);
+  });
+
+  it("returns null and logs once when IPC returns NaN", async () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    invokeDesktopCommandMock.mockResolvedValueOnce(Number.NaN);
+
+    const idleTimeMs = await getDesktopSystemIdleTimeMs();
+
+    expect(idleTimeMs).toBeNull();
+    expect(warn).toHaveBeenCalledTimes(1);
+    expect(warn).toHaveBeenCalledWith("[DesktopIdle] Invalid system idle time", Number.NaN);
+  });
+
+  it("returns null and logs once when IPC returns a negative value", async () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    invokeDesktopCommandMock.mockResolvedValueOnce(-1);
+
+    const idleTimeMs = await getDesktopSystemIdleTimeMs();
+
+    expect(idleTimeMs).toBeNull();
+    expect(warn).toHaveBeenCalledTimes(1);
+    expect(warn).toHaveBeenCalledWith("[DesktopIdle] Invalid system idle time", -1);
+  });
+
+  it("returns 0 when IPC returns zero", async () => {
+    invokeDesktopCommandMock.mockResolvedValueOnce(0);
+
+    const idleTimeMs = await getDesktopSystemIdleTimeMs();
+
+    expect(idleTimeMs).toBe(0);
+  });
+});

packages/app/src/desktop/electron/idle.ts

@@ -0,0 +1,21 @@
+import { invokeDesktopCommand } from "@/desktop/electron/invoke";
+
+const DESKTOP_SYSTEM_IDLE_COMMAND = "desktop_get_system_idle_time";
+
+function isValidIdleTimeMs(value: unknown): value is number {
+  return typeof value === "number" && Number.isFinite(value) && value >= 0;
+}
+
+export async function getDesktopSystemIdleTimeMs(): Promise<number | null> {
+  try {
+    const idleTimeMs = await invokeDesktopCommand<unknown>(DESKTOP_SYSTEM_IDLE_COMMAND);
+    if (!isValidIdleTimeMs(idleTimeMs)) {
+      console.warn("[DesktopIdle] Invalid system idle time", idleTimeMs);
+      return null;
+    }
+    return idleTimeMs;
+  } catch (error) {
+    console.warn("[DesktopIdle] Failed to read system idle time", error);
+    return null;
+  }
+}

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

@@ -0,0 +1,215 @@
+import React, { act } from "react";
+import { createRoot, type Root } from "react-dom/client";
+import { JSDOM } from "jsdom";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { useClientActivity } from "./use-client-activity";
+
+type HeartbeatPayload = {
+  deviceType: "web" | "mobile";
+  focusedAgentId: string | null;
+  lastActivityAt: string;
+  appVisible: boolean;
+  appVisibilityChangedAt?: string;
+};
+
+const { platformState, getDesktopSystemIdleTimeMs } = vi.hoisted(() => ({
+  platformState: {
+    isWeb: true,
+    isNative: false,
+    isElectron: false,
+  },
+  getDesktopSystemIdleTimeMs: vi.fn<() => Promise<number | null>>(),
+}));
+
+vi.mock("@/constants/platform", () => ({
+  get isWeb() {
+    return platformState.isWeb;
+  },
+  get isNative() {
+    return platformState.isNative;
+  },
+  getIsElectron: () => platformState.isElectron,
+}));
+
+vi.mock("@/desktop/electron/idle", () => ({
+  getDesktopSystemIdleTimeMs,
+}));
+
+vi.mock("react-native", () => ({
+  AppState: {
+    currentState: "active",
+    addEventListener: vi.fn(() => ({
+      remove: vi.fn(),
+    })),
+  },
+}));
+
+vi.mock("@server/client/daemon-client", () => ({}));
+
+function createTestClient() {
+  return {
+    isConnected: true,
+    subscribeConnectionStatus: vi.fn(() => vi.fn()),
+    sendHeartbeat: vi.fn<(payload: HeartbeatPayload) => void>(),
+  };
+}
+
+function latestHeartbeat(client: ReturnType<typeof createTestClient>): HeartbeatPayload {
+  const call = client.sendHeartbeat.mock.calls.at(-1);
+  if (!call) {
+    throw new Error("Expected a heartbeat");
+  }
+  return call[0];
+}
+
+function heartbeatTimeMs(client: ReturnType<typeof createTestClient>): number {
+  return new Date(latestHeartbeat(client).lastActivityAt).getTime();
+}
+
+async function renderActivityHook({
+  client = createTestClient(),
+}: {
+  client?: ReturnType<typeof createTestClient>;
+} = {}) {
+  function Probe() {
+    useClientActivity({
+      client: client as unknown as Parameters<typeof useClientActivity>[0]["client"],
+      focusedAgentId: "agent-1",
+    });
+    return null;
+  }
+
+  const container = document.createElement("div");
+  document.body.appendChild(container);
+  const root = createRoot(container);
+
+  await act(async () => {
+    root.render(<Probe />);
+  });
+
+  return { client, root };
+}
+
+async function advance(ms: number) {
+  await act(async () => {
+    await vi.advanceTimersByTimeAsync(ms);
+  });
+}
+
+describe("useClientActivity", () => {
+  let root: Root | null = null;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-04-19T10:00:00.000Z"));
+
+    platformState.isWeb = true;
+    platformState.isNative = false;
+    platformState.isElectron = false;
+    getDesktopSystemIdleTimeMs.mockReset();
+
+    const dom = new JSDOM("<!doctype html><html><body></body></html>", {
+      url: "http://localhost",
+    });
+    vi.stubGlobal("IS_REACT_ACT_ENVIRONMENT", true);
+    vi.stubGlobal("window", dom.window);
+    vi.stubGlobal("document", dom.window.document);
+  });
+
+  afterEach(async () => {
+    if (root) {
+      await act(async () => {
+        root?.unmount();
+      });
+      root = null;
+    }
+    vi.unstubAllGlobals();
+    vi.useRealTimers();
+  });
+
+  it("updates lastActivityAt from web pointer activity", async () => {
+    const rendered = await renderActivityHook();
+    root = rendered.root;
+
+    vi.setSystemTime(new Date("2026-04-19T10:00:05.250Z"));
+    window.dispatchEvent(new window.Event("pointerdown"));
+
+    expect(heartbeatTimeMs(rendered.client)).toBe(Date.now());
+    expect(getDesktopSystemIdleTimeMs).not.toHaveBeenCalled();
+  });
+
+  it("drives lastActivityAt forward from Electron idle polling", async () => {
+    platformState.isElectron = true;
+    getDesktopSystemIdleTimeMs.mockResolvedValue(0);
+    const rendered = await renderActivityHook();
+    root = rendered.root;
+
+    await advance(5_000);
+    expect(getDesktopSystemIdleTimeMs).toHaveBeenCalledTimes(1);
+
+    await advance(10_000);
+
+    expect(heartbeatTimeMs(rendered.client)).toBe(Date.now());
+  });
+
+  it("sets lastActivityAt to Date.now() minus the Electron idle time", async () => {
+    platformState.isElectron = true;
+    getDesktopSystemIdleTimeMs.mockResolvedValue(2_000);
+    const rendered = await renderActivityHook();
+    root = rendered.root;
+
+    await advance(5_000);
+    await advance(10_000);
+
+    expect(heartbeatTimeMs(rendered.client)).toBe(Date.now() - 2_000);
+  });
+
+  it("skips failed Electron idle polls", async () => {
+    platformState.isElectron = true;
+    getDesktopSystemIdleTimeMs.mockResolvedValue(null);
+    const rendered = await renderActivityHook();
+    root = rendered.root;
+    const previousLastActivityAt = heartbeatTimeMs(rendered.client);
+
+    await advance(5_000);
+    await advance(10_000);
+
+    expect(heartbeatTimeMs(rendered.client)).toBe(previousLastActivityAt);
+  });
+
+  it("never moves lastActivityAt backward from an idle poll", async () => {
+    platformState.isElectron = true;
+    getDesktopSystemIdleTimeMs.mockResolvedValue(20_000);
+    const rendered = await renderActivityHook();
+    root = rendered.root;
+
+    vi.setSystemTime(new Date("2026-04-19T10:00:05.000Z"));
+    window.dispatchEvent(new window.Event("pointerdown"));
+    const pointerActivityAt = latestHeartbeat(rendered.client).lastActivityAt;
+
+    await advance(5_000);
+    expect(getDesktopSystemIdleTimeMs).toHaveBeenCalled();
+
+    await advance(10_000);
+
+    expect(latestHeartbeat(rendered.client).lastActivityAt).toBe(pointerActivityAt);
+  });
+
+  it("keeps an Electron pointerdown newer than a stale idle poll", async () => {
+    platformState.isElectron = true;
+    getDesktopSystemIdleTimeMs.mockResolvedValue(20_000);
+    const rendered = await renderActivityHook();
+    root = rendered.root;
+
+    await advance(4_500);
+    window.dispatchEvent(new window.Event("pointerdown"));
+    const pointerActivityAt = latestHeartbeat(rendered.client).lastActivityAt;
+
+    await advance(500);
+    expect(getDesktopSystemIdleTimeMs).toHaveBeenCalled();
+
+    await advance(10_000);
+
+    expect(latestHeartbeat(rendered.client).lastActivityAt).toBe(pointerActivityAt);
+  });
+});

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

@@ -1,10 +1,12 @@
 import { useEffect, useRef, useCallback } from "react";
 import { AppState } from "react-native";
 import type { DaemonClient } from "@server/client/daemon-client";
-import { isWeb, isNative } from "@/constants/platform";
+import { getIsElectron, isWeb, isNative } from "@/constants/platform";
+import { getDesktopSystemIdleTimeMs } from "@/desktop/electron/idle";
 
 const HEARTBEAT_INTERVAL_MS = 15_000;
 const ACTIVITY_HEARTBEAT_THROTTLE_MS = 5_000;
+const DESKTOP_IDLE_POLL_INTERVAL_MS = 5_000;
 
 interface ClientActivityOptions {
   client: DaemonClient;
@@ -130,6 +132,31 @@ export function useClientActivity({
     };
   }, [maybeSendImmediateHeartbeat, recordUserActivity, setAppVisible]);
 
+  // Track OS-wide activity in Electron so backgrounded desktop windows still report presence.
+  useEffect(() => {
+    if (!getIsElectron()) return;
+
+    let disposed = false;
+    const pollSystemIdleTime = async () => {
+      const systemIdleMs = await getDesktopSystemIdleTimeMs();
+      if (disposed || systemIdleMs === null) return;
+
+      const systemLastActivityAtMs = Date.now() - systemIdleMs;
+      if (systemLastActivityAtMs > lastActivityAtRef.current.getTime()) {
+        lastActivityAtRef.current = new Date(systemLastActivityAtMs);
+      }
+    };
+
+    const interval = setInterval(() => {
+      void pollSystemIdleTime();
+    }, DESKTOP_IDLE_POLL_INTERVAL_MS);
+
+    return () => {
+      disposed = true;
+      clearInterval(interval);
+    };
+  }, [client]);
+
   // Send heartbeat on focused agent change
   useEffect(() => {
     if (prevFocusedAgentIdRef.current !== focusedAgentId) {