Merge origin/main into t3/frame-comfort-alerts

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+- Add an opt-in desktop low-battery alert without starting a family session.
+  Existing status reads confirm low charge and drain; recovery hysteresis and a
+  ten-minute cooldown limit repeat alerts. Off on page open/headset switch;
+  pauses with hidden-page status refreshes. No extra polling or headset changes.
+
 - Clarify first-time desktop downloads, installation and opening on the website
   and README, including CPU choices, unsigned-app warnings, pairing fallback
   and the source-only iOS build. Keep section navigation available on mobile.

docs/evidence/desktop-battery-comfort-2026-10-24.json

@@ -0,0 +1,95 @@
+{
+  "date": "2026-10-24",
+  "command": "scripts/frame-power-sample.sh --count 2 --interval 1",
+  "exitCode": 0,
+  "stopped": null,
+  "lockPolicy": "Existing sampler checked local and remote /tmp/frame-test.lock before reading; no lock acquired, bypassed or removed. Read-only run only.",
+  "samples": [
+    {
+      "time": 1792828506.4317346,
+      "osBuild": "20261015.6141207",
+      "elapsedSeconds": 0.057539,
+      "battery": {
+        "battery.percent": {
+          "value": 99,
+          "unit": "%",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        },
+        "battery.status": {
+          "value": "Not charging",
+          "unit": "state",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        },
+        "battery.watts": {
+          "value": -0.06,
+          "unit": "W",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        },
+        "battery.tempC": {
+          "value": 24.0,
+          "unit": "C",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        }
+      }
+    },
+    {
+      "time": 1792828507.4357972,
+      "osBuild": "20261015.6141207",
+      "elapsedSeconds": 1.061612,
+      "battery": {
+        "battery.percent": {
+          "value": 99,
+          "unit": "%",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        },
+        "battery.status": {
+          "value": "Not charging",
+          "unit": "state",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        },
+        "battery.watts": {
+          "value": -0.05,
+          "unit": "W",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        },
+        "battery.tempC": {
+          "value": 24.0,
+          "unit": "C",
+          "source": "/sys/class/power_supply/max1720x_bat_7-36",
+          "state": "available"
+        }
+      }
+    }
+  ],
+  "limitations": [
+    "No real low-charge or thermal condition induced.",
+    "No native notification delivery verified.",
+    "No worn-headset or native package tests.",
+    "Read-only parser/transport check; no background monitor or power-saving claim."
+  ],
+  "browserCheck": {
+    "page": "Production ui/index.html served statically; API calls intentionally unavailable",
+    "viewport": {
+      "width": 1280,
+      "height": 800
+    },
+    "bridge": "Synthetic desktop notification bridge; no native OS notification sent",
+    "result": "Initially unchecked and visible only after desktop host/bridge setup. Checkbox enabled through browser. Synthetic 12%, Discharging, -4 W samples at 0/30/60 seconds produced one bridge request, an in-page status and a toast. No horizontal overflow.",
+    "apiLimit": "Static server returned expected 404/501 API errors; not an end-to-end live desktop connection test."
+  },
+  "offlineValidation": [
+    "test_desktop_battery_comfort.py: 2 tests, production JS with monotonic fake clock and notification bridge",
+    "test_comfort*.py: 25 tests",
+    "test_battery.py: 7 tests",
+    "test_power*.py: 36 tests (loopback HTTP test run outside socket-restricted sandbox)",
+    "test_ui_workspace.py: 1 Python wrapper / Node workspace suite",
+    "test_ui_review.py: 1 Python wrapper / 9 Node regression tests, including switch reset and retained cooldown"
+  ]
+}

docs/family-comfort.md

@@ -6,6 +6,45 @@ This is Frame Control code using Python, Steam and SteamVR already on the Frame.
 
 ![Family and comfort controls in the desktop app](img/comfort-desktop.png)
 
+## Desktop low-battery alert without a session
+
+In the desktop app, open **Tools → Family & comfort** and check **Alert on this
+computer at 15% or less**. This separate option does not start a session, install
+a worker or change the headset. It starts off whenever the page opens and turns
+off when you switch headsets. The choice is only for the current open page.
+
+It consumes the battery parser already used by normal status refreshes (also
+shared by the read-only power sampler). It adds no SSH calls, timers, sensor
+reads, third-party push or heat thresholds. Normal automatic status refreshes
+pause while the page is hidden, so this is **not a background or safety monitor**.
+Keep the app visible and connected. Use **Enable / test notifications** to check
+system delivery; operating-system settings may block notifications.
+
+Two fresh readings, at least 20 seconds and at most 90 seconds apart, must show
+15% or less, driver state `Discharging`, and signed battery power below −0.5 W.
+This avoids alerting on plugged-in idle readings, which can report discharging.
+Missing, invalid, stale or interrupted readings break confirmation. Disconnect,
+a failed status request, hiding the page or toggling the option also breaks
+confirmation. Unknown readings never mean zero charge.
+
+An alert appears in the page and requests a native desktop notification once
+per low-charge episode. Two readings at 20% or more rearm it, and at least ten
+minutes must pass between alerts (including across headset switches). A single
+recovery spike cannot rearm it. Toggling off/on does not clear the episode latch.
+Notification failure stays visible in the page and does not retry on every
+refresh. While an active family session has battery alerts enabled, that session
+handles battery alerts instead. Multiple app windows have independent state;
+this does not coordinate notifications between computers or windows.
+
+A read-only check on 2026-10-24, build **20261015.6141207**, received two samples
+at 99%, `Not charging`, approximately −0.06 W and 24 °C. No low-battery condition
+was induced, no notification was sent to the real headset, and no headset state
+was changed. The sampler's local and remote smoke-lock checks allowed the run;
+no lock was acquired or removed. Deterministic tests exercise low charge,
+recovery, missing readings, idle drain, timing and notification denial. See
+[recorded evidence](evidence/desktop-battery-comfort-2026-10-24.json). Native OS
+notification display, worn use and macOS/Windows packaging were not verified.
+
 ## Sessions
 
 Set a limit of 1–240 minutes, optional break and check-in intervals, then

tests/control_center.cjs

@@ -23,7 +23,8 @@ function fixture() {
   const page = element('controlCenter');
   page.querySelectorAll = selector => selector === '[data-cc-category]' ? buttons : selector === '[data-cc-metric]' ? metrics : selector === '[data-cc-mac-link]' ? [element('macLink')] : [];
   page.querySelector = selector => selector === '[href="#connection"]' ? element('connectionLink') : cards.find(e=>selector === `[data-cc-card="${e.dataset.ccCard}"]`);
-  return {document:{getElementById:element},element,cards,buttons};
+  const listeners = {};
+  return {document:{hidden:false,getElementById:element,addEventListener(name,callback){listeners[name]=callback;}},listeners,element,cards,buttons};
 }
 function mounted(options = {}) {
   const f = fixture(), calls = [];
@@ -39,8 +40,10 @@ const flush = async () => { for(let i=0;i<12;i++)await Promise.resolve(); };
 // bootstrap, including the real Home-to-Control status handoff. Only unrelated
 // rendering helpers, timers and transport are stubbed.
 function sharedPage({productionApi=false} = {}) {
-  const f=fixture(), requests=[], writes=[], host=deferred(), job=deferred();
-  const context={document:f.document,FrameControlCenter:cc,window:{frameApp:{setUpConnection(){}}},
+  const f=fixture(), requests=[], writes=[], notifications=[], host=deferred(), job=deferred();
+  let now=0;
+  const context={document:f.document,FrameControlCenter:cc,performance:{now:()=>now},
+    window:{frameApp:{setUpConnection(){},notify:async(message,request)=>{notifications.push({message,request});}}},
     Date,setInterval,clearInterval,setTimeout:()=>1,clearTimeout(){},$:f.element,QUICK:[],installing:new Set(),
     battery(){},setVolume(){},renderHome(){},gb:String,dur:String,esc:String,meter(){},toast(){},
     runJob(title,id){context.installing.add(id);return job.promise;},
@@ -52,7 +55,11 @@ function sharedPage({productionApi=false} = {}) {
     watchConnection(){context.watched=true;}};
   vm.createContext(context);
   const stateDeclaration=pageSource.match(/let state = null[^\n]*/)[0];
-  vm.runInContext(stateDeclaration+'\nlet online = true, devGen = 1; const HOST = {computer:"computer"}; window.connDevice="frame-a";',context);
+  vm.runInContext(stateDeclaration+'\nlet online = true, devGen = 1, comfortActive = false; const HOST = {computer:"computer"}; window.connDevice="frame-a";',context);
+  // Load the real alert state machine and DOM wiring used by render, refresh,
+  // setOnline and onConnection; do not stub away their lifecycle behavior.
+  const batteryStart=pageSource.indexOf('class DesktopBatteryAlert'),batteryEnd=pageSource.indexOf('// ---- battery ----',batteryStart);
+  vm.runInContext(pageSource.slice(batteryStart,batteryEnd),context);
   const refreshStart=pageSource.indexOf('let refreshing = null'),refreshEnd=pageSource.indexOf('// ---- our VR HUD',refreshStart);
   const renderStart=pageSource.indexOf('function render(s) {'),renderEnd=pageSource.indexOf('// ---- view ----',renderStart);
   vm.runInContext(pageSource.slice(renderStart,renderEnd)+pageSource.slice(refreshStart,refreshEnd),context);
@@ -80,12 +87,48 @@ function sharedPage({productionApi=false} = {}) {
   const hostStart=pageSource.lastIndexOf('api("/api/host").then(h =>'),hostEnd=pageSource.indexOf('</script>',hostStart);
   vm.runInContext(pageSource.slice(hostStart,hostEnd),context);
   const bootstrapStart=pageSource.indexOf('window.frameControlCenter = FrameControlCenter.mount('),bootstrapEnd=pageSource.indexOf('</script>',bootstrapStart);
-  return {...f,context,requests,writes,host,refresh:()=>vm.runInContext('refresh()',context),
+  return {...f,context,requests,writes,notifications,host,setNow(value){now=value;},refresh:()=>vm.runInContext('refresh()',context),
     switchHeadset:()=>vm.runInContext('onConnection({now:Date.now()/1000,phase:"connected",devices_rev:0,device:{id:"frame-b",name:"Second Frame"}})',context),
     installFlatpak:()=>vm.runInContext('installFlatpak("test.app")',context),
     mount(){vm.runInContext(pageSource.slice(bootstrapStart,bootstrapEnd),context);return context.window.frameControlCenter;}};
 }
 const response = data => ({ok:true,status:200,json:async()=>data});
+test('production refresh confirms desktop alerts and failures interrupt confirmation', async () => {
+  const f=sharedPage({productionApi:true});
+  const low=sample();low.battery={percent:15,status:'Discharging',watts:-4};
+  const read=async(now,data=low)=>{
+    f.setNow(now);const pending=f.refresh();
+    f.requests.at(-1).resolve(response(data));await pending;
+  };
+  await read(0);await read(30000);
+  assert.equal(f.notifications.length,0,'desktop alert starts off');
+  f.element('desktopBatteryAlert').checked=true;
+  f.element('desktopBatteryAlert').onchange();
+  await read(60000);
+  const failed=f.refresh();f.requests.at(-1).reject(Error('Status transport failed'));await failed;
+  await read(90000);
+  assert.equal(f.notifications.length,0,'failed status interrupts low-battery confirmation');
+  await read(120000);
+  assert.equal(f.notifications.length,1);
+  assert.match(f.notifications[0].message,/15%.*draining/);
+  assert.equal(f.notifications[0].request,false,'refresh never requests notification permission');
+  await read(150000);
+  assert.equal(f.notifications.length,1,'same episode stays latched');
+  assert.equal(f.requests.length,7,'only explicit existing status reads are used');
+});
+test('production headset switch clears desktop opt-in and pending confirmation', async () => {
+  const f=sharedPage({productionApi:true});
+  f.element('desktopBatteryAlert').checked=true;
+  const low=sample();low.battery={percent:10,status:'Discharging',watts:-3};
+  const pending=f.refresh();f.requests[0].resolve(response(low));await pending;
+  assert.equal(vm.runInContext('desktopBattery.pending.condition',f.context),'low');
+  f.setNow(30000);f.switchHeadset();
+  assert.equal(f.element('desktopBatteryAlert').checked,false);
+  assert.equal(vm.runInContext('desktopBattery.pending',f.context),null);
+  assert.match(f.element('desktopBatteryStatus').textContent,/Headset changed/);
+  f.requests[1].resolve(response(low));await flush();
+  assert.equal(f.notifications.length,0,'new headset cannot inherit the prior opt-in');
+});
 for(const rejection of ['transport','body'])for(const delayedMount of [false,true]) {
   test(`production ${rejection} rejection from A preserves B ${delayedMount ? 'before delayed mount' : 'after mount'}`, async t => {
     const f=sharedPage({productionApi:true});

tests/test_desktop_battery_comfort.py

@@ -0,0 +1,105 @@
+"""Exercise the shipped desktop alert and its UI with a monotonic fake clock."""
+import pathlib
+import shutil
+import subprocess
+import unittest
+
+ROOT = pathlib.Path(__file__).resolve().parents[1]
+
+
+@unittest.skipUnless(shutil.which('node'), 'Node exercises production page JavaScript')
+class DesktopBatteryComfort(unittest.TestCase):
+    def test_alert_confirmation_and_lifecycle(self):
+        page = (ROOT / 'ui/index.html').read_text(encoding='utf-8')
+        code = page.split('// ---- Desktop-only low-battery comfort:')[1].split('// ---- battery ----')[0]
+        code = code[code.index('class DesktopBatteryAlert'):]
+        js = r'''
+const assert = require('node:assert/strict');
+const elements = new Map();
+const $ = id => {
+  if (!elements.has(id)) elements.set(id, {checked:false, textContent:''});
+  return elements.get(id);
+};
+let now = 0, calls = [], toasts = [], devGen = 1, comfortActive = false;
+const performance = {now:()=>now};
+const listeners = {};
+const document = {hidden:false, addEventListener:(name,fn)=>listeners[name]=fn};
+const HOST = {mobile:false};
+const window = {frameApp:{notify:(message,request)=>{calls.push({message,request});return Promise.resolve();}}};
+const toast = message => toasts.push(message);
+''' + code + r'''
+(async () => {
+  const low = {percent:15,status:'Discharging',watts:-4};
+  const high = {...low,percent:20};
+  const a = new DesktopBatteryAlert();
+  assert.equal(a.sample(low,0),false);
+  assert.equal(a.sample(low,1000),false); // rapid manual refreshes cannot confirm
+  assert.equal(a.sample(low,30000),true);
+  for (let t=60000;t<=900000;t+=30000) assert.equal(a.sample(low,t),false);
+  assert.equal(a.sample(high,930000),false);
+  assert.equal(a.sample(low,960000),false); // a recovery spike did not rearm
+  assert.equal(a.sample(low,990000),false);
+  a.sample(high,1020000); a.sample(high,1050000);
+  assert.equal(a.sample(low,1080000),false);
+  assert.equal(a.sample(low,1110000),true);
+  const c = new DesktopBatteryAlert();
+  c.sample(low,0); assert.equal(c.sample(low,30000),true);
+  c.sample(high,60000); c.sample(high,90000);
+  c.sample(low,120000); assert.equal(c.sample(low,150000),false); // ten minute cap
+  assert.equal(c.sample(low,631000),false); // long gap requires fresh confirmation
+  assert.equal(c.sample(low,661000),true);
+  for (const bad of [null,{}, {...low,percent:null}, {...low,percent:NaN}, {...low,percent:-1},
+      {...low,percent:101},{...low,percent:'10'}, {...low,status:'Unknown'},
+      {...low,status:'Charging'}, {...low,status:'Full'}, {...low,status:'Not charging'},
+      {...low,watts:0},{...low,watts:-0.5},{...low,watts:null},{...low,watts:NaN}]) {
+    const b = new DesktopBatteryAlert();
+    b.sample(low,0); assert.equal(b.sample(bad,30000),false);
+    assert.equal(b.sample(low,60000),false); // unknown interrupts confirmation
+  }
+  const b = new DesktopBatteryAlert();
+  b.sample(low,0); b.invalidate(); assert.equal(b.sample(low,30000),false);
+  assert.equal(b.sample(low,121000),false); // stale gap
+  assert.equal(b.sample(low,120000),false); // clock rollback
+  desktopBatterySample(low); now=30000; desktopBatterySample(low);
+  assert.equal(calls.length,0); // opt-in starts unchecked
+  $('desktopBatteryAlert').checked=true; $('desktopBatteryAlert').onchange();
+  now=60000;desktopBatterySample(low);now=90000;desktopBatterySample(low);
+  assert.equal(calls.length,1); assert.equal(calls[0].request,false);
+  assert.match(calls[0].message,/15%.*draining/);
+  $('desktopBatteryAlert').checked=false;$('desktopBatteryAlert').onchange();
+  $('desktopBatteryAlert').checked=true;$('desktopBatteryAlert').onchange();
+  now=120000;desktopBatterySample(low);now=150000;desktopBatterySample(low);
+  assert.equal(calls.length,1); // toggling does not clear episode latch
+  desktopBattery.latched=false;desktopBattery.lastAlert=-Infinity;desktopBattery.invalidate();
+  now=180000;desktopBatterySample(low);document.hidden=true;listeners.visibilitychange();
+  document.hidden=false;now=210000;desktopBatterySample(low);assert.equal(calls.length,1);
+  now=240000;desktopBatterySample(low);assert.equal(calls.length,2);
+  desktopBattery.latched=false;desktopBattery.lastAlert=-Infinity;desktopBattery.invalidate();
+  comfortActive=true;$('batteryAlert').checked=true;
+  now=270000;desktopBatterySample(low);now=300000;desktopBatterySample(low);
+  assert.equal(calls.length,2); // existing session owns battery alerts
+  comfortActive=false;HOST.mobile=true;
+  now=330000;desktopBatterySample(low);now=360000;desktopBatterySample(low);
+  assert.equal(calls.length,2);
+  HOST.mobile=false;
+  window.frameApp.notify=()=>Promise.reject(Error('denied'));
+  now=390000;desktopBatterySample(low);now=420000;desktopBatterySample(low);
+  await new Promise(setImmediate);
+  assert.match($('desktopBatteryStatus').textContent,/not confirmed/);
+  now=450000;desktopBatterySample(low);
+  assert.equal(toasts.length,3); // delivery failure does not retry on refresh
+})().catch(e=>{console.error(e);process.exitCode=1;});
+'''
+        result = subprocess.run(['node', '-e', js], capture_output=True, text=True)
+        self.assertEqual(result.returncode, 0, result.stderr)
+
+    def test_existing_status_path_and_switch_reset(self):
+        page = (ROOT / 'ui/index.html').read_text(encoding='utf-8')
+        self.assertIn('desktopBatterySample(s.battery);', page)
+        switch = page.split('if (link.device !== null && devId !== link.device)')[1].split('devGen++;')[0]
+        self.assertIn('$("desktopBatteryAlert").checked = false;', switch)
+        refresh = page.split('function refresh()')[1].split('async function refreshAfterAudio')[0]
+        self.assertIn('desktopBattery.invalidate();', refresh)
+        block = page.split('// ---- Desktop-only low-battery comfort:')[1].split('// ---- battery ----')[0]
+        self.assertNotIn('setTimeout', block)
+        self.assertNotIn('api(', block)

tests/ui_review.cjs

@@ -10,6 +10,8 @@ function connectionFixture() {
     sourceState:{jobs:new Map(),detail:null,detailRequest:0},touches:new Map(),gesture:null,padType:{blur(){},value:''},
     log(){},renderPill(){},renderConnDlg(){},renderHome(){},resetShots(){},resetClips(){},renderBanner(){},loadDevices(){},renderDevices(){},renderTests(){},viaText(){return 'test';},netLabel(){return 'test';},refresh:()=>Promise.resolve(),reloadAll(){},checkContactPrompt(){},ctrlReset(){},padShow:s=>{c.pad.state=s.state;}});
   c.window.connDevice='a';
+  c.document.addEventListener=()=>{};
+  f.run(pick(html,'class DesktopBatteryAlert {','// ---- battery ----'));
   f.run('const UI_KEY="test";'+pick(html,'const HEADSET_FREE =','// What a panel shows'));
   f.run(pick(html,'function onConnection(s) {','// Read the event stream'));
   return f;
@@ -41,8 +43,15 @@ test('a device switch discards completed install results and the open detail',()
   Object.assign(c,{pad:{state:'off',queue:[]},padReset(){},sourceState:{jobs:new Map([['test:one',{done:true,result:{package:'app.on.a',game_data:true}}]]),detail:{app:{}},detailRequest:0}});
   f.el('appDetail').open=true;
   f.el('storageResult').textContent='Old headset storage';
+  f.el('desktopBatteryAlert').checked=true;
+  f.run('desktopBattery.pending={condition:"low",at:0};desktopBattery.latched=true;desktopBattery.lastAlert=42;');
   f.run('onConnection({phase:"connected",device:{id:"b",name:"B"},devices_rev:1,now:0})');
   assert.match(f.el('storageResult').textContent,/Headset changed/);
+  assert.equal(f.el('desktopBatteryAlert').checked,false);
+  assert.equal(f.run('desktopBattery.pending'),null);
+  assert.equal(f.run('desktopBattery.latched'),false);
+  assert.equal(f.run('desktopBattery.lastAlert'),42);
+  assert.match(f.el('desktopBatteryStatus').textContent,/Off.*Headset changed/);
   assert.equal(c.sourceState.jobs.size,0);assert.equal(c.sourceState.detail,null);assert.equal(f.el('appDetail').open,false);
 });
 test('only a preview matching current diagnostics consent can be sent or copied',async()=>{

ui/index.html

@@ -1465,6 +1465,12 @@
     </details>
   </section><section class="panel" id="comfort" style="margin:20px 0;padding:16px">
     <div class="shelf-head"><h2>Family and comfort</h2><span class="count">Session timer and reminders</span></div>
+    <div id="desktopBatteryComfort" hidden>
+      <h3>Desktop low-battery alert</h3>
+      <label><input id="desktopBatteryAlert" type="checkbox"> Alert on this computer at 15% or less</label>
+      <p class="hint">No session timer needed. Off when this page opens or you switch headsets. Uses normal status refreshes while the page is visible; no extra polling or headset changes. Two readings must confirm low charge and battery drain. One alert until charge recovers to 20%, with at least ten minutes between alerts.</p>
+      <p id="desktopBatteryStatus" class="hint" role="status">Off.</p>
+    </div>
     <form id="comfortForm">
       <div class="row" style="flex-wrap:wrap;gap:12px">
         <label>Session limit (minutes) <input id="sessionMinutes" type="number" min="1" max="240" value="30" required style="width:75px"></label>
@@ -2130,6 +2136,7 @@ const HOST = { computer: "computer" };
 function applyHostWording(h) {
   Object.assign(HOST, h);
   window.frameControlCenter?.host(h);
+  $("desktopBatteryComfort").hidden = !!h.mobile || !window.frameApp?.notify;
   // The iPhone app: the server runs on the Frame, and saving goes to the phone's Photos.
   document.body.classList.toggle("mobile", !!h.mobile);
   $("shotsFolder").hidden = !!h.mobile;
@@ -2240,6 +2247,7 @@ function setOnline(ok, why) {
   if (HOST.mobile) $('mobileConnectionStatus').textContent = ok ? 'Connected to the Frame serving this session.' : 'The Frame is disconnected. Retry or check its address in connection setup.';
   $('offline').hidden = ok;
   if (!ok) {
+    desktopBattery.invalidate();
     $("offMsg").textContent = why || "Can't reach the Frame";
     setConn(false, "Offline");
     $("battChip").hidden = true; closeDevPop();
@@ -2276,6 +2284,7 @@ function refresh() {
       setConn(true, state.hostname);
       setOnline(true);
     } catch (e) {
+      desktopBattery.invalidate();
       renderPerformance(null);
       if (!e.stale) stateRead = {valid: false, error: e};
       renderHome();
@@ -2456,6 +2465,60 @@ $("castBtn").onclick = () => {
   $("viewer").requestFullscreen?.().catch(() => {});
 };
 
+// ---- Desktop-only low-battery comfort: consumes existing status, never polls ----
+class DesktopBatteryAlert {
+  constructor() {
+    this.pending = null;
+    this.latched = false;
+    this.lastAlert = -Infinity;
+  }
+  invalidate() { this.pending = null; }
+  sample(b, now) {
+    // Require actual drain as well as driver state: plugged-in idle can report Discharging.
+    const valid = Number.isFinite(b?.percent) && b.percent >= 0 && b.percent <= 100 &&
+      ["Charging", "Discharging", "Full", "Not charging"].includes(b.status);
+    const low = valid && b.percent <= 15 && b.status === "Discharging" &&
+      Number.isFinite(b.watts) && b.watts < -0.5;
+    const recovered = valid && b.percent >= 20;
+    const condition = low ? "low" : recovered ? "recovered" : null;
+    if (!condition) { this.invalidate(); return false; }
+    if (!this.pending || this.pending.condition !== condition || now - this.pending.at > 90000 || now < this.pending.at) {
+      this.pending = {condition, at: now};
+      return false;
+    }
+    if (now - this.pending.at < 20000) return false;
+    if (recovered) this.latched = false;
+    if (!low || this.latched || now - this.lastAlert < 600000) return false;
+    this.latched = true;
+    this.lastAlert = now;  // latch even when system delivery fails; never retry on each refresh
+    return true;
+  }
+}
+const desktopBattery = new DesktopBatteryAlert();
+$("desktopBatteryAlert").onchange = () => {
+  desktopBattery.invalidate();
+  $("desktopBatteryStatus").textContent = $("desktopBatteryAlert").checked
+    ? "On. Waiting for two fresh status readings confirming low charge and battery drain."
+    : "Off.";
+};
+function desktopBatterySample(b) {
+  if (!$("desktopBatteryAlert").checked || HOST.mobile || !window.frameApp?.notify || document.hidden ||
+      (comfortActive && $("batteryAlert").checked)) {
+    desktopBattery.invalidate();
+    return;
+  }
+  if (!desktopBattery.sample(b, performance.now())) return;
+  const message = `Frame battery is low (${b.percent}%) and draining. Consider charging or taking a break.`;
+  $("desktopBatteryStatus").textContent = message;
+  toast(message);
+  // Desktop bridge only: never prompt or send a phone/browser push from a status refresh.
+  const generation = devGen;
+  window.frameApp.notify(message, false).catch(() => {
+    if (generation !== devGen || !$("desktopBatteryAlert").checked) return;
+    $("desktopBatteryStatus").textContent = message + " System notification delivery was not confirmed. Check system settings or use Enable / test notifications below.";
+  });
+}
+document.addEventListener("visibilitychange", () => desktopBattery.invalidate());
 // ---- battery ----
 function battery(b, power) {
   const pct = b?.percent;
@@ -2511,6 +2574,7 @@ function render(s) {
   renderHome(s);
   window.frameControlCenter?.status(s, stateReceivedAt, stateRead);
   battery(s.battery, s.power);
+  desktopBatterySample(s.battery);
   $("devPopTitle").textContent = $("devPopTitle").title = window.connName || "Headset";
   $("devName").textContent = `${s.hostname} · ${s.ip ?? "no IP"}`;
   $("updated").textContent = new Date(s.time * 1000).toLocaleTimeString();
@@ -6898,6 +6962,11 @@ function onConnection(s) {
     stateReceivedAt = null;
     stateRead = {valid: false, error: null};
     online = null;
+    $("desktopBatteryAlert").checked = false;
+    desktopBattery.invalidate();
+    // Keep the cooldown across switches, but a new headset can start its own charge episode.
+    desktopBattery.latched = false;
+    $("desktopBatteryStatus").textContent = "Off. Headset changed; enable for this headset if wanted.";
     devGen++;               // answers still on their way are about the other headset
     padReset(); ctrlReset();
     sourceState.jobs.clear(); sourceState.detail = null; sourceState.detailRequest++;