diff --git a/src/main/ipc/runtime-environments/runtime-environment-request-connections.ts b/src/main/ipc/runtime-environments/runtime-environment-request-connections.ts
index e866d2a3b25..78f09b3dc3d 100644
--- a/src/main/ipc/runtime-environments/runtime-environment-request-connections.ts
+++ b/src/main/ipc/runtime-environments/runtime-environment-request-connections.ts
@@ -313,7 +313,7 @@ function getSharedControlConnection(
     sharedControlConnections.set(environmentId, cached)
     const entry = cached
     // Why ready is enough: a socket reaches ready only on its own server frame, which stamps it.
-    setSharedControlAnswerSource(environmentId, () =>
+    setSharedControlAnswerSource(environmentId, entry.connection, () =>
       entry.connection.getDiagnostics().state === 'ready' ? entry.answeredAt() : null
     )
   }
diff --git a/src/main/ipc/runtime-environments/runtime-environment-shared-control-answers.ts b/src/main/ipc/runtime-environments/runtime-environment-shared-control-answers.ts
index 5b310e9294d..992c22704cb 100644
--- a/src/main/ipc/runtime-environments/runtime-environment-shared-control-answers.ts
+++ b/src/main/ipc/runtime-environments/runtime-environment-shared-control-answers.ts
@@ -1,14 +1,33 @@
 /**
- * When each environment's ready control socket last heard from its server. A leaf module: the
- * serving gate reads it without importing the connection cache, which imports the gate back.
+ * Each environment's control socket and when it last heard from its server while ready. A leaf
+ * module: the serving gate reads it without importing the connection cache, which imports the gate back.
  */
-const sources = new Map<string, () => number | null>()
+export type SharedControlSocket = {
+  isReady(): boolean
+  readonly socketGeneration: { peek(): number }
+  request(method: string, params: unknown, timeoutMs: number): Promise<unknown>
+}
+
+/** A ready control socket; `socket` changes whenever it reconnects or the connection is replaced. */
+export type ReadySharedControlSocket = {
+  environmentId: string
+  socket: string
+  request: SharedControlSocket['request']
+}
+
+const sources = new Map<
+  string,
+  { connection: SharedControlSocket; answeredAt: () => number | null; instance: number }
+>()
+// Why: a replacement connection restarts its socket generation, so the key needs the instance too.
+let nextInstance = 0
 
 export function setSharedControlAnswerSource(
   environmentId: string,
-  source: () => number | null
+  connection: SharedControlSocket,
+  answeredAt: () => number | null
 ): void {
-  sources.set(environmentId, source)
+  sources.set(environmentId, { connection, answeredAt, instance: ++nextInstance })
 }
 
 export function clearSharedControlAnswerSource(environmentId: string): void {
@@ -17,5 +36,21 @@ export function clearSharedControlAnswerSource(environmentId: string): void {
 
 /** Null while there is no ready control socket for the environment. */
 export function getRemoteRuntimeSharedControlAnsweredAt(environmentId: string): number | null {
-  return sources.get(environmentId)?.() ?? null
+  return sources.get(environmentId)?.answeredAt() ?? null
+}
+
+/** Every ready control socket, without opening one. */
+export function listReadySharedControlSockets(): ReadySharedControlSocket[] {
+  return [...sources.entries()].flatMap(([environmentId, { connection, instance }]) =>
+    connection.isReady()
+      ? [
+          {
+            environmentId,
+            socket: `${instance}:${connection.socketGeneration.peek()}`,
+            request: (method: string, params: unknown, timeoutMs: number) =>
+              connection.request(method, params, timeoutMs)
+          }
+        ]
+      : []
+  )
 }
diff --git a/src/main/notifications/desktop-presence-reporter.test.ts b/src/main/notifications/desktop-presence-reporter.test.ts
new file mode 100644
index 00000000000..2f8873343fc
--- /dev/null
+++ b/src/main/notifications/desktop-presence-reporter.test.ts
@@ -0,0 +1,82 @@
+import { expect, it, vi } from 'vitest'
+import { DESKTOP_PRESENCE_REPORT_INTERVAL_MS } from '../../shared/desktop-client-presence'
+import {
+  clearSharedControlAnswerSource,
+  listReadySharedControlSockets,
+  setSharedControlAnswerSource
+} from '../ipc/runtime-environments/runtime-environment-shared-control-answers'
+import { createDesktopPresenceReporter } from './desktop-presence-reporter'
+
+it('reports on change, on a new socket and as a keepalive, and never reports unknown as present', async () => {
+  let away: boolean | undefined = false
+  let now = 0
+  let socket = '1'
+  const request = vi.fn(async (_method: string, _params: unknown, _timeoutMs: number) => ({
+    ok: true
+  }))
+  const listTargets = vi.fn(() => [{ environmentId: 'ssh-host', socket, request }])
+  const reporter = createDesktopPresenceReporter({
+    readAway: () => away,
+    listTargets,
+    now: () => now
+  })
+  const tick = reporter.tick
+  const reported = () => request.mock.calls.map((call) => call[1])
+
+  tick()
+  tick()
+  expect(listTargets).toHaveBeenCalledWith('notifications.desktop-presence.v1')
+  expect(reported()).toEqual([{ away: false }])
+  away = undefined
+  tick()
+  expect(reported()).toEqual([{ away: false }, { away: true }])
+  now += DESKTOP_PRESENCE_REPORT_INTERVAL_MS
+  tick()
+  expect(reported()).toHaveLength(3)
+  away = false
+  socket = '2'
+  now += 1
+  tick()
+  socket = '3'
+  tick()
+  expect(reported()).toEqual([
+    { away: false },
+    { away: true },
+    { away: true },
+    { away: false },
+    { away: false }
+  ])
+
+  request.mockRejectedValueOnce(new Error('socket closed'))
+  socket = '4'
+  tick()
+  await Promise.resolve()
+  await Promise.resolve()
+  tick()
+  expect(reported()).toHaveLength(7)
+  // Suspend reports away at once and holds it while the idle clock still reads active.
+  reporter.setForcedAway(true)
+  expect(reported().at(-1)).toEqual({ away: true })
+  now += DESKTOP_PRESENCE_REPORT_INTERVAL_MS
+  tick()
+  expect(reported().at(-1)).toEqual({ away: true })
+  reporter.setForcedAway(false)
+  expect(reported().at(-1)).toEqual({ away: false })
+})
+
+it('keys a replaced connection apart from the one it replaced, though both start at generation 1', () => {
+  const connection = () => ({
+    isReady: () => true,
+    socketGeneration: { peek: () => 1 },
+    request: async () => ({ ok: true })
+  })
+  try {
+    setSharedControlAnswerSource('replaced-host', connection(), () => null)
+    const [before] = listReadySharedControlSockets()
+    setSharedControlAnswerSource('replaced-host', connection(), () => null)
+    const [after] = listReadySharedControlSockets()
+    expect(after.socket).not.toBe(before.socket)
+  } finally {
+    clearSharedControlAnswerSource('replaced-host')
+  }
+})
diff --git a/src/main/notifications/desktop-presence-reporter.ts b/src/main/notifications/desktop-presence-reporter.ts
new file mode 100644
index 00000000000..3977ed7ebd5
--- /dev/null
+++ b/src/main/notifications/desktop-presence-reporter.ts
@@ -0,0 +1,113 @@
+import {
+  DESKTOP_PRESENCE_REPORT_INTERVAL_MS,
+  NOTIFICATIONS_DESKTOP_PRESENCE_RUNTIME_CAPABILITY
+} from '../../shared/desktop-client-presence'
+import { getRuntimeEnvironmentStatusSnapshots } from '../ipc/runtime-environments/runtime-environment-request-connections'
+import {
+  listReadySharedControlSockets,
+  type ReadySharedControlSocket
+} from '../ipc/runtime-environments/runtime-environment-shared-control-answers'
+
+/** How often local idle state is sampled, so a return to the desk reaches hosts within seconds. */
+const SAMPLE_INTERVAL_MS = 5_000
+const REPORT_TIMEOUT_MS = 10_000
+
+type Sent = { socket: string; away: boolean; at: number }
+
+export type DesktopPresenceReporterDeps = {
+  readAway: () => boolean | undefined
+  listTargets: (capability: string) => ReadySharedControlSocket[]
+  now?: () => number
+}
+
+/**
+ * Tells each connected host whether someone is at this desktop, so a headless host can honor a
+ * phone's "only when desktop is away" (#31570). Sent on change, on a new socket, and as a keepalive.
+ */
+export type DesktopPresenceReporter = {
+  tick(): void
+  /** Latched across ticks, so a sample between suspend and sleep cannot report present. */
+  setForcedAway(forced: boolean): void
+}
+
+export function createDesktopPresenceReporter(
+  deps: DesktopPresenceReporterDeps
+): DesktopPresenceReporter {
+  const now = deps.now ?? Date.now
+  const sent = new Map<string, Sent>()
+  let forcedAway = false
+  const tick = (): void => {
+    const targets = deps.listTargets(NOTIFICATIONS_DESKTOP_PRESENCE_RUNTIME_CAPABILITY)
+    if (targets.length === 0) {
+      sent.clear()
+      return
+    }
+    // Why: unknown local presence must never silence a phone, so only a proven "active" is present.
+    const away = forcedAway || deps.readAway() !== false
+    const at = now()
+    const live = new Set(targets.map((target) => target.environmentId))
+    for (const environmentId of sent.keys()) {
+      if (!live.has(environmentId)) {
+        sent.delete(environmentId)
+      }
+    }
+    for (const target of targets) {
+      const last = sent.get(target.environmentId)
+      if (
+        last &&
+        last.socket === target.socket &&
+        last.away === away &&
+        at - last.at < DESKTOP_PRESENCE_REPORT_INTERVAL_MS
+      ) {
+        continue
+      }
+      const entry = { socket: target.socket, away, at }
+      sent.set(target.environmentId, entry)
+      // Why: a refused report waits for the keepalive; only an unsent one retries on the next tick.
+      void target
+        .request('notifications.reportDesktopPresence', { away }, REPORT_TIMEOUT_MS)
+        .catch(() => {
+          if (sent.get(target.environmentId) === entry) {
+            sent.delete(target.environmentId)
+          }
+        })
+    }
+  }
+  return {
+    tick,
+    setForcedAway: (forced) => {
+      forcedAway = forced
+      tick()
+    }
+  }
+}
+
+/** Ready control sockets whose host's last status advertised `capability`. */
+export function listCapableSharedControlSockets(capability: string): ReadySharedControlSocket[] {
+  const capable = new Set(
+    getRuntimeEnvironmentStatusSnapshots()
+      .filter((snapshot) => snapshot.status?.capabilities?.includes(capability))
+      .map((snapshot) => snapshot.environmentId)
+  )
+  return listReadySharedControlSockets().filter((target) => capable.has(target.environmentId))
+}
+
+export function startDesktopPresenceReporter(
+  deps: DesktopPresenceReporterDeps & {
+    /** Sleep and screen lock report away at once and hold it until resume or unlock. */
+    subscribePowerEvents: (handlers: { away: () => void; back: () => void }) => () => void
+  }
+): () => void {
+  const reporter = createDesktopPresenceReporter(deps)
+  const timer = setInterval(reporter.tick, SAMPLE_INTERVAL_MS)
+  // Why: presence reporting must never hold the app open at quit.
+  timer.unref?.()
+  const unsubscribe = deps.subscribePowerEvents({
+    away: () => reporter.setForcedAway(true),
+    back: () => reporter.setForcedAway(false)
+  })
+  return () => {
+    clearInterval(timer)
+    unsubscribe()
+  }
+}
diff --git a/src/main/runtime/desktop-client-presence-tracker.ts b/src/main/runtime/desktop-client-presence-tracker.ts
new file mode 100644
index 00000000000..b2139553e16
--- /dev/null
+++ b/src/main/runtime/desktop-client-presence-tracker.ts
@@ -0,0 +1,32 @@
+import { DESKTOP_PRESENCE_TTL_MS } from '../../shared/desktop-client-presence'
+
+/** The last presence each attached desktop connection reported to this host. */
+export class DesktopClientPresenceTracker {
+  private readonly reports = new Map<string, { away: boolean; at: number }>()
+
+  has(connectionId: string): boolean {
+    return this.reports.has(connectionId)
+  }
+
+  report(connectionId: string, away: boolean, now: number): void {
+    this.reports.set(connectionId, { away, at: now })
+  }
+
+  forget(connectionId: string): void {
+    this.reports.delete(connectionId)
+  }
+
+  /** True only on a fresh "present" report; silence, staleness and older desktops read as away. */
+  anyPresent(now: number): boolean {
+    let present = false
+    for (const [connectionId, { away, at }] of this.reports) {
+      if (now - at >= DESKTOP_PRESENCE_TTL_MS) {
+        // Why prune: the next report re-registers the forget-on-close, so nothing can pile up.
+        this.reports.delete(connectionId)
+      } else if (!away) {
+        present = true
+      }
+    }
+    return present
+  }
+}
diff --git a/src/main/runtime/push/push-policy-pipeline.integration.test.ts b/src/main/runtime/push/push-policy-pipeline.integration.test.ts
index 47ba42052f8..0e806205bfc 100644
--- a/src/main/runtime/push/push-policy-pipeline.integration.test.ts
+++ b/src/main/runtime/push/push-policy-pipeline.integration.test.ts
@@ -6,6 +6,9 @@ import { readDesktopAwayState } from '../../notifications/desktop-away-state'
 import { DeviceRegistry } from '../device-registry'
 import { RuntimeMobileNotificationController } from '../runtime-mobile-notification-controller'
 import { setRuntimeDesktopSurface } from '../runtime-desktop-surface'
+import { RuntimeSubscriptionRegistry } from '../runtime-subscription-registry'
+import { reportDesktopPresence } from '../rpc/methods/notifications'
+import { DESKTOP_PRESENCE_TTL_MS } from '../../../shared/desktop-client-presence'
 import { DesktopPushService } from './desktop-push-service'
 import { PushUnregisterOutbox } from './push-unregister-outbox'
 import { createPushHostKeypair } from './push-host-challenge-fixtures'
@@ -103,15 +106,55 @@ it('carries the native idle boundary through replay and push dispatch', async ()
   )
 })
 
-it('keeps headless presence unknown and legacy socket events readable', async () => {
+it('decides headless away from attached desktops, so the away-only filter holds on orca serve', async () => {
+  const now = 1_800_000_000_000
+  const clock = vi.spyOn(Date, 'now').mockReturnValue(now)
   setRuntimeDesktopSurface(null)
   const h = await pipeline()
-  const events: unknown[] = []
-  h.controller.onDispatched((event) => events.push(JSON.parse(JSON.stringify(event))))
-  h.dispatch()
-  await flush()
-  expect(events[0]).not.toHaveProperty('desktopAway')
-  expect(h.client.send).toHaveBeenCalledTimes(1)
+  const subscriptions = new RuntimeSubscriptionRegistry()
+  const runtime = {
+    reportDesktopClientPresence: h.controller.reportDesktopClientPresence.bind(h.controller),
+    registerSubscriptionCleanup: subscriptions.register.bind(subscriptions)
+  }
+  const desktop: {
+    runtime: typeof runtime
+    clientKind?: 'mobile' | 'runtime'
+    connectionId: string
+  } = { runtime, clientKind: 'runtime', connectionId: 'desktop-socket' }
+  const report = (
+    away: boolean,
+    context: Partial<typeof desktop> & { signal?: AbortSignal } = {}
+  ) => reportDesktopPresence({ away }, { ...desktop, ...context })
+  const sends = async () => {
+    h.dispatch()
+    await flush()
+    return h.client.send.mock.calls.length
+  }
+
+  // No desktop has ever reported: nobody is at one.
+  expect(await sends()).toBe(1)
+  // Neither a phone nor a socket that already closed can vouch for a desktop.
+  expect(report(false, { clientKind: 'mobile' })).toEqual({ recorded: false })
+  expect(report(false, { signal: AbortSignal.abort() })).toEqual({ recorded: false })
+  expect(await sends()).toBe(2)
+  report(false)
+  expect(await sends()).toBe(2)
+  report(true)
+  expect(await sends()).toBe(3)
+  report(false)
+  expect(await sends()).toBe(3)
+  // A desktop that stops reporting (or an older one that never did) lapses to away.
+  clock.mockReturnValue(now + DESKTOP_PRESENCE_TTL_MS)
+  expect(await sends()).toBe(4)
+  report(false)
+  expect(await sends()).toBe(4)
+  subscriptions.cleanupForConnection('desktop-socket')
+  expect(await sends()).toBe(5)
+  expect(
+    h.controller
+      .getMissedSince(0)
+      .map((event) => (event.type === 'notification' ? event.desktopAway : null))
+  ).toEqual([true, true, false, true, false, true, false, true])
 })
 
 it('expires persisted registration at seven days despite host activity and renews explicitly', async () => {
diff --git a/src/main/runtime/rpc/methods/notifications.ts b/src/main/runtime/rpc/methods/notifications.ts
index cca473aa975..8959d0d4cca 100644
--- a/src/main/runtime/rpc/methods/notifications.ts
+++ b/src/main/runtime/rpc/methods/notifications.ts
@@ -1,8 +1,10 @@
 import { createNotificationStreamFilter } from './notification-stream-policy'
-import { defineStreamingMethod, defineMethod } from '../core'
+import { defineStreamingMethod, defineMethod, type RpcContext } from '../core'
+import type { OrcaRuntimeService } from '../../orca-runtime'
 import {
   NotificationGetMissedSinceParams,
   NotificationRegisterPushParams,
+  NotificationReportDesktopPresenceParams,
   NotificationUnsubscribeParams,
   NotificationsSubscribeParams
 } from '../../../../shared/rpc-contract/notifications-params'
@@ -12,6 +14,25 @@ import {
 // notifications.subscribe calls landed on the same millisecond.
 let notificationsSubscriptionSeq = 0
 
+type DesktopPresenceReportContext = Pick<RpcContext, 'clientKind' | 'connectionId' | 'signal'> & {
+  runtime: Pick<OrcaRuntimeService, 'reportDesktopClientPresence' | 'registerSubscriptionCleanup'>
+}
+
+/** Only a paired desktop's own socket speaks for a desktop; the report lives as long as it. */
+export function reportDesktopPresence(
+  params: { away: boolean },
+  { runtime, clientKind, connectionId, signal }: DesktopPresenceReportContext
+): { recorded: boolean } {
+  // A closed socket already ran its cleanups, so a late report would never be forgotten.
+  if (clientKind !== 'runtime' || !connectionId || signal?.aborted) {
+    return { recorded: false }
+  }
+  runtime.reportDesktopClientPresence(connectionId, params.away, (forget) =>
+    runtime.registerSubscriptionCleanup(`desktop-presence-${connectionId}`, forget, connectionId)
+  )
+  return { recorded: true }
+}
+
 // Legacy callers retain filtered socket alerts; push clients opt into the full event stream.
 export const NOTIFICATION_METHODS = [
   defineStreamingMethod({
@@ -76,6 +97,12 @@ export const NOTIFICATION_METHODS = [
       }
     }
   }),
+  defineMethod({
+    name: 'notifications.reportDesktopPresence',
+    permission: 'workspace',
+    params: NotificationReportDesktopPresenceParams,
+    handler: async (params, context) => reportDesktopPresence(params, context)
+  }),
   defineMethod({
     name: 'notifications.registerPush',
     permission: 'pairing-admin',
diff --git a/src/main/runtime/runtime-desktop-surface.ts b/src/main/runtime/runtime-desktop-surface.ts
index 4738da82cd0..94b1d007ea0 100644
--- a/src/main/runtime/runtime-desktop-surface.ts
+++ b/src/main/runtime/runtime-desktop-surface.ts
@@ -18,8 +18,9 @@ import type { BrowserWindow, IpcMainEvent } from 'electron'
 export type RuntimeDesktopSurface = {
   /** Headless hosts retain the formatter's English defaults. */
   translateNotification?(key: string, fallback: string): string
-  /** Show a native notification. Returns false when the host cannot, so callers can say so. */
+  /** This machine's own idle state; undefined is unknown. Absent on hosts with no desktop. */
   isAwayForMobileNotifications?(): boolean | undefined
+  /** Show a native notification. Returns false when the host cannot, so callers can say so. */
   showNotification(input: { title: string; body: string }): boolean
   /** The renderer window with this id, or null when there is no desktop. */
   findWindowById(id: number): BrowserWindow | null
diff --git a/src/main/runtime/runtime-mobile-notification-controller.ts b/src/main/runtime/runtime-mobile-notification-controller.ts
index 90792771dbe..3849466ca78 100644
--- a/src/main/runtime/runtime-mobile-notification-controller.ts
+++ b/src/main/runtime/runtime-mobile-notification-controller.ts
@@ -16,6 +16,7 @@ import { MobileNotificationReplayBuffer } from './mobile-notification-replay'
 import { notifyRuntimeListeners } from './runtime-async-boundaries'
 import { getRuntimeDesktopSurface } from './runtime-desktop-surface'
 import { MobileNotificationDismissalStore } from './mobile-notification-dismissal-store'
+import { DesktopClientPresenceTracker } from './desktop-client-presence-tracker'
 import type { DeliveredNotificationIdentity } from '../../shared/mobile-notification-identity'
 
 export type MobileNotificationDispatchEvent = {
@@ -66,6 +67,7 @@ export class RuntimeMobileNotificationController {
   private readonly replay = new MobileNotificationReplayBuffer()
   private pushRegistrar: MobilePushRegistrar | null = null
   private dismissalStore: MobileNotificationDismissalStore | null = null
+  private readonly desktopClients = new DesktopClientPresenceTracker()
 
   configureDismissalStore(userDataPath: string): void {
     this.dismissalStore = new MobileNotificationDismissalStore(userDataPath)
@@ -107,6 +109,29 @@ export class RuntimeMobileNotificationController {
     return (await this.pushRegistrar?.unregister(deviceId)) ?? { unregistered: false }
   }
 
+  /** `bindForget` runs for a connection without a live report, before it is recorded. */
+  reportDesktopClientPresence(
+    connectionId: string,
+    away: boolean,
+    bindForget: (forget: () => void) => void
+  ): void {
+    if (!this.desktopClients.has(connectionId)) {
+      bindForget(() => this.desktopClients.forget(connectionId))
+    }
+    this.desktopClients.report(connectionId, away, Date.now())
+  }
+
+  // Why: undefined means unknown and must never silence a phone; only a fresh report or the local
+  // idle state proves someone is at a desktop. A host with no desktop of its own (orca serve) has
+  // only its attached desktops to ask, so their silence is away rather than unknown (#31570).
+  private resolveDesktopAway(): boolean | undefined {
+    if (this.desktopClients.anyPresent(Date.now())) {
+      return false
+    }
+    const surface = getRuntimeDesktopSurface()
+    return surface.isAwayForMobileNotifications ? surface.isAwayForMobileNotifications() : true
+  }
+
   onDispatched(listener: (event: MobileNotificationEvent) => void): () => void {
     this.listeners.add(listener)
     return () => this.listeners.delete(listener)
@@ -130,7 +155,7 @@ export class RuntimeMobileNotificationController {
       event = {
         ...event,
         legacySocketAllowed,
-        desktopAway: getRuntimeDesktopSurface().isAwayForMobileNotifications?.()
+        desktopAway: this.resolveDesktopAway()
       }
     }
     const seq = this.replay.record(event)
diff --git a/src/main/runtime/runtime-service-command-surface.ts b/src/main/runtime/runtime-service-command-surface.ts
index f0a66279f64..461090f7dbd 100644
--- a/src/main/runtime/runtime-service-command-surface.ts
+++ b/src/main/runtime/runtime-service-command-surface.ts
@@ -30,6 +30,7 @@ export type RuntimeServiceCommandSurface = {
   onNotificationDispatched: RuntimeMobileNotificationController['onDispatched']
   getMobileNotificationListenerCount: RuntimeMobileNotificationController['getListenerCount']
   dispatchMobileNotification: RuntimeMobileNotificationController['dispatch']
+  reportDesktopClientPresence: RuntimeMobileNotificationController['reportDesktopClientPresence']
   getMissedNotificationsSince: RuntimeMobileNotificationController['getMissedSince']
   configureNotificationDismissalStore: RuntimeMobileNotificationController['configureDismissalStore']
   closeNotificationDismissals: RuntimeMobileNotificationController['closeDismissals']
@@ -138,6 +139,7 @@ export function installRuntimeServiceCommandSurface(
     onNotificationDispatched: notifications.onDispatched.bind(notifications),
     getMobileNotificationListenerCount: notifications.getListenerCount.bind(notifications),
     dispatchMobileNotification: notifications.dispatch.bind(notifications),
+    reportDesktopClientPresence: notifications.reportDesktopClientPresence.bind(notifications),
     getMissedNotificationsSince: notifications.getMissedSince.bind(notifications),
     configureNotificationDismissalStore: notifications.configureDismissalStore.bind(notifications),
     closeNotificationDismissals: notifications.closeDismissals.bind(notifications),
diff --git a/src/main/startup/main-process-observers-hang-breadcrumb.test.ts b/src/main/startup/main-process-observers-hang-breadcrumb.test.ts
index 70f84476f3d..3f0d32593f1 100644
--- a/src/main/startup/main-process-observers-hang-breadcrumb.test.ts
+++ b/src/main/startup/main-process-observers-hang-breadcrumb.test.ts
@@ -37,6 +37,10 @@ vi.mock('../agent-awake-service', () => ({
 vi.mock('../system-resume-broadcast', () => ({
   registerSystemResumeBroadcast: () => () => {}
 }))
+vi.mock('../notifications/desktop-presence-reporter', () => ({
+  listCapableSharedControlSockets: () => [],
+  startDesktopPresenceReporter: () => () => {}
+}))
 vi.mock('../agent-hooks/server', () => ({
   agentHookServer: {
     subscribeStatusChanges: () => () => {},
diff --git a/src/main/startup/main-process-observers.ts b/src/main/startup/main-process-observers.ts
index 2204de397e5..ed8084e4986 100644
--- a/src/main/startup/main-process-observers.ts
+++ b/src/main/startup/main-process-observers.ts
@@ -1,8 +1,13 @@
-import { app } from 'electron'
+import { app, powerMonitor } from 'electron'
 import { join } from 'node:path'
 import { AgentAwakeService } from '../agent-awake-service'
 import { normalizeComputerAwakeMode } from '../../shared/computer-awake-mode'
 import { registerSystemResumeBroadcast } from '../system-resume-broadcast'
+import { readDesktopAwayState } from '../notifications/desktop-away-state'
+import {
+  listCapableSharedControlSockets,
+  startDesktopPresenceReporter
+} from '../notifications/desktop-presence-reporter'
 import { agentHookServer } from '../agent-hooks/server'
 import { installHookStatusSessionTabsRepublish } from '../agent-hooks/hook-status-session-tabs-republish'
 import { initTelemetry, track } from '../telemetry/client'
@@ -29,6 +34,22 @@ export function initializeMainProcessObservers(): void {
     throw new Error('Store must be initialized before observers')
   }
   state.unsubscribeSystemResumeBroadcast = registerSystemResumeBroadcast()
+  state.stopDesktopPresenceReporter = startDesktopPresenceReporter({
+    readAway: () => readDesktopAwayState(powerMonitor),
+    listTargets: listCapableSharedControlSockets,
+    subscribePowerEvents: ({ away, back }) => {
+      powerMonitor.on('suspend', away)
+      powerMonitor.on('lock-screen', away)
+      powerMonitor.on('resume', back)
+      powerMonitor.on('unlock-screen', back)
+      return () => {
+        powerMonitor.off('suspend', away)
+        powerMonitor.off('lock-screen', away)
+        powerMonitor.off('resume', back)
+        powerMonitor.off('unlock-screen', back)
+      }
+    }
+  })
   state.agentAwakeService = new AgentAwakeService()
   state.agentAwakeService.setMode(
     normalizeComputerAwakeMode(
diff --git a/src/main/startup/main-process-quit.ts b/src/main/startup/main-process-quit.ts
index e4be252abdd..12ce061671b 100644
--- a/src/main/startup/main-process-quit.ts
+++ b/src/main/startup/main-process-quit.ts
@@ -120,6 +120,8 @@ function installWillQuitHandler(): void {
     state.desktopPushService?.stop()
     state.unsubscribeSystemResumeBroadcast?.()
     state.unsubscribeSystemResumeBroadcast = null
+    state.stopDesktopPresenceReporter?.()
+    state.stopDesktopPresenceReporter = null
     // Why: renderer guards can still cancel before this committed phase; `log stream` must survive those vetoes.
     stopTccPromptNotice()
     const updateQuitInProgress = isQuittingForUpdate()
diff --git a/src/main/startup/main-process-state.ts b/src/main/startup/main-process-state.ts
index 94f2b1bb0e2..09fa8b10fbc 100644
--- a/src/main/startup/main-process-state.ts
+++ b/src/main/startup/main-process-state.ts
@@ -103,6 +103,8 @@ export const mainProcessState = {
   crashReports: null as CrashReportStore | null,
   unsubscribeAgentAwakeStatusChanges: null as (() => void) | null,
   unsubscribeSystemResumeBroadcast: null as (() => void) | null,
+  // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: widens the null slot to the stop function assigned by main-process-observers.
+  stopDesktopPresenceReporter: null as (() => void) | null,
   watcherShutdownPromise: null as Promise<void> | null,
   watcherShutdownDone: false,
   automations: null as AutomationService | null,
diff --git a/src/shared/desktop-client-presence.ts b/src/shared/desktop-client-presence.ts
new file mode 100644
index 00000000000..a5c9e7fbdee
--- /dev/null
+++ b/src/shared/desktop-client-presence.ts
@@ -0,0 +1,10 @@
+// Why: an older host answers notifications.reportDesktopPresence with method-not-found, so a desktop
+// reports only to a host advertising this; an older desktop never reports and reads as away.
+export const NOTIFICATIONS_DESKTOP_PRESENCE_RUNTIME_CAPABILITY =
+  'notifications.desktop-presence.v1' as const
+
+/** A desktop re-reports this often while connected, so the host can expire a silent one. */
+export const DESKTOP_PRESENCE_REPORT_INTERVAL_MS = 30_000
+
+/** A report older than this no longer counts: three missed reports read as away. */
+export const DESKTOP_PRESENCE_TTL_MS = 3 * DESKTOP_PRESENCE_REPORT_INTERVAL_MS
diff --git a/src/shared/mobile-runtime-capabilities.ts b/src/shared/mobile-runtime-capabilities.ts
index 34ce8f765e9..b0571300d7d 100644
--- a/src/shared/mobile-runtime-capabilities.ts
+++ b/src/shared/mobile-runtime-capabilities.ts
@@ -1,3 +1,4 @@
+import { NOTIFICATIONS_DESKTOP_PRESENCE_RUNTIME_CAPABILITY } from './desktop-client-presence'
 import { MOBILE_RELAY_RUNTIME_CAPABILITIES } from './mobile-desktop-relay-contract'
 
 // Hosts without this capability have no notifications.registerPush RPC.
@@ -6,5 +7,6 @@ export const NOTIFICATIONS_REMOTE_PUSH_RUNTIME_CAPABILITY = 'notifications.remot
 export const MOBILE_RUNTIME_CAPABILITIES = [
   'mobile.tasks.v1',
   NOTIFICATIONS_REMOTE_PUSH_RUNTIME_CAPABILITY,
+  NOTIFICATIONS_DESKTOP_PRESENCE_RUNTIME_CAPABILITY,
   ...MOBILE_RELAY_RUNTIME_CAPABILITIES
 ] as const
diff --git a/src/shared/rpc-contract/notifications-params.ts b/src/shared/rpc-contract/notifications-params.ts
index 6ae2cd45f5e..e436ffcfb67 100644
--- a/src/shared/rpc-contract/notifications-params.ts
+++ b/src/shared/rpc-contract/notifications-params.ts
@@ -59,3 +59,5 @@ export const NotificationRegisterPushParams = z
 export const NotificationsSubscribeParams = z
   .object({ includeDesktopSuppressed: z.boolean().optional() })
   .optional()
+
+export const NotificationReportDesktopPresenceParams = z.object({ away: z.boolean() })
diff --git a/src/shared/rpc-contract/rpc-params-catalog.generated.ts b/src/shared/rpc-contract/rpc-params-catalog.generated.ts
index 311d0ae208a..9de0bee6e74 100644
--- a/src/shared/rpc-contract/rpc-params-catalog.generated.ts
+++ b/src/shared/rpc-contract/rpc-params-catalog.generated.ts
@@ -404,6 +404,7 @@ import { NativeChatSession, NativeChatUnsubscribe } from './native-chat-params'
 import {
   NotificationGetMissedSinceParams,
   NotificationRegisterPushParams,
+  NotificationReportDesktopPresenceParams,
   NotificationUnsubscribeParams,
   NotificationsSubscribeParams
 } from './notifications-params'
@@ -1165,6 +1166,7 @@ export const RPC_PARAMS_BY_METHOD = {
   'network.browserTunnel': BrowserNetworkTunnelAttachParams,
   'notifications.getMissedSince': NotificationGetMissedSinceParams,
   'notifications.registerPush': NotificationRegisterPushParams,
+  'notifications.reportDesktopPresence': NotificationReportDesktopPresenceParams,
   'notifications.subscribe': NotificationsSubscribeParams,
   'notifications.testPush': null,
   'notifications.unregisterPush': null,