Document Linux PC-host feasibility blocker on lxso2

Co-authored-by: SAPHID <saphid@users.noreply.github.com>

CHANGELOG.md

@@ -2,6 +2,16 @@
 
 ## Unreleased
 
+- Distinguish an unreadable gamescope panel list from a confirmed empty list in
+  Desktop Capture and Control (issue #73). Failed discovery now asks users to
+  check SteamVR and report the exact message and SteamOS version, rather than
+  claiming no panel is open. This does not establish a new capture fix.
+
+- 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.

app/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "frame-control",
-  "version": "0.4.16",
+  "version": "0.4.17",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "frame-control",
-      "version": "0.4.16",
+      "version": "0.4.17",
       "license": "MIT",
       "devDependencies": {
         "electron": "^44.4.5",

app/package.json

@@ -1,7 +1,7 @@
 {
   "name": "frame-control",
   "productName": "Frame Control",
-  "version": "0.4.16",
+  "version": "0.4.17",
   "description": "Desktop app for managing a Valve Steam Frame over SSH",
   "private": true,
   "main": "main.js",

docs/evidence/clip-gui-export-2026-10-24.json

@@ -0,0 +1,38 @@
+{
+  "date_utc": "2026-10-24T07:54:37Z",
+  "frame_control_tag": "v0.4.16",
+  "steamos_version": "0.5.6",
+  "steamos_build": "20261015.6141207",
+  "host": "lxso2",
+  "interface": "source UI served by a temporary private Frame Control server, opened in T3 Code's desktop browser",
+  "action": "Clicked the visible Export button for Steam's retained real saved clip in Capture & Live",
+  "clip_id": "10230640/clips/clip_13009719723623972864_20261024_072115",
+  "api_observed": {
+    "post_clips_export_http": 200,
+    "get_job_http": 200,
+    "get_clips_http": 200
+  },
+  "ui_result": "Saved clip_13009719723623972864_20261024_072115.mp4 to ~/Videos/SteamFrame; button changed to Export again",
+  "output": {
+    "path": "~/Videos/SteamFrame/clip_13009719723623972864_20261024_072115.mp4",
+    "bytes": 159829,
+    "sha256": "f8a476eefb2bde7ba5cb464632ec9b952eea3ab1610b5bed2098bf1f11d62cf1",
+    "matches_previously_fully_decoded_export": true,
+    "duration_seconds": 10.288532,
+    "video": "H.264 1920x1080",
+    "audio": "AAC stereo"
+  },
+  "cleanup": {
+    "temporary_server_stopped": true,
+    "shared_device_lock_released": true,
+    "battery_percent_after": 99,
+    "desktop_mode_active_after": false,
+    "test_title_created": false,
+    "steam_source_clip_retained": true
+  },
+  "limits": [
+    "The test used the source UI, not a packaged desktop installer.",
+    "The retained source clip was nearly black; visible gameplay capture remains unverified.",
+    "Perceptual audio/video sync, long clips, trims and automatic copying were not tested."
+  ]
+}

docs/evidence/clip-long-2026-10-24.json

@@ -0,0 +1,29 @@
+{
+  "date_utc": "2026-10-24",
+  "version": "v0.4.17",
+  "steam_os_version": "0.5.6",
+  "steam_os_build": "20261015.6141207",
+  "result": "PASS: the real Steam-saved clip exported beyond 60 seconds",
+  "method": "Steam manual recording of a reserved test title, then Frame Control's production frame_clips.export_clip path; no packaged GUI button click",
+  "source": {
+    "kind": "saved Steam clip",
+    "duration_seconds": 100.801,
+    "chunks": 68,
+    "gaps": 0
+  },
+  "export": {
+    "format": "MP4",
+    "bytes": 1377849,
+    "sha256": "82ef31f65e6933d122bc326d664beb2eb2e3ba6969f26c0032552e80fbe8d823",
+    "duration_seconds_ffprobe": 100.833335,
+    "video": "H.264, 1920x1080, 6049 frames",
+    "audio": "AAC, 48000 Hz, stereo",
+    "full_ffmpeg_decode": "passed without errors"
+  },
+  "cleanup": "Restored Steam recording mode to its prior off setting; stopped and removed only the reserved title and its processes; no recording or running Steam apps remained; Game Mode active, battery 100%, shared test lock released",
+  "limits": [
+    "This exercised the production export code path, not a packaged GUI Export click.",
+    "Visible gameplay quality, perceptual audio/video sync, trims and longer recordings were not checked.",
+    "The newly saved Steam source clip was retained; no user recording was deleted."
+  ]
+}

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/evidence/linux-pc-host-lxso2-2026-10-24.md

@@ -0,0 +1,114 @@
+# Linux PC host feasibility on lxso2, 2026-10-24
+
+**Blocked on this host's current desktop environment. No feature enabled and
+no feature PR opened.** Investigation for [issue #23](https://github.com/saphid/frame-control/issues/23),
+starting at `4e45648` (main after #154). This concerns flat desktop panels,
+not Linux PC VR streaming.
+
+## Decision
+
+The smallest useful candidate is one explicitly selected **whole screen**,
+captured through the ScreenCast portal's restricted PipeWire connection,
+encoded locally with GStreamer/x264, and sent to the existing viewer through
+the shared SSH controller. Input, individual windows and virtual displays
+would remain unsupported until separately verified. This candidate was **not
+implemented**: lxso2 currently cannot exercise the real capture permission path.
+
+Development packages could unblock compilation, but would not create a desktop,
+portal backend or consented screen. Synthetic encoding, an Xvfb screen grab or
+using the Frame as its own host would not verify Linux PC desktop capture.
+No host packages or services were changed.
+
+## Evidence
+
+Host: `lxso2`, Linux x86-64, kernel `6.8.0-139-generic`.
+
+- `DISPLAY`, `WAYLAND_DISPLAY` and `XDG_SESSION_TYPE` were unset. The user bus
+  was reachable at `/run/user/1000/bus`.
+- `/run/user/1000/pipewire-0` and `/run/user/1000/wayland-0` did not exist.
+  No processes matched Xorg, Xwayland, Xvfb, GNOME Shell, KWin Wayland, Weston,
+  PipeWire, WirePlumber or xdg-desktop-portal at the process check.
+- D-Bus `ListNames` returned D-Bus, systemd and anonymous connections, with no
+  `org.freedesktop.portal.Desktop`. `ListActivatableNames` also had no desktop
+  portal. These calls queried D-Bus itself without activating capture services.
+- `dpkg-query` found no `xdg-desktop-portal*` or `pipewire*` packages.
+  `libgstreamer1.0-0:amd64` was installed at `1.24.2-1ubuntu0.1`, but
+  `gstreamer1.0-tools` was uninstalled. `gst-launch-1.0` and `gst-inspect-1.0`
+  were absent from PATH. Xvfb was installed, but supplies no portal by itself.
+- `pkg-config --modversion` failed for `gstreamer-1.0`,
+  `gstreamer-app-1.0`, `gstreamer-video-1.0` and `libpipewire-0.3`.
+  `gio-unix-2.0` reported `2.80.0`.
+- `desktop/bundle/pc-host.so` did not exist.
+  `python3 desktop/build.py --with-x264 --out /tmp/frame-linux-pc-feasibility`
+  exited **1** before compilation: required GStreamer pkg-config modules were
+  missing. No native build or encoder runtime success is claimed.
+
+Reproduce the non-activating portal checks in the intended desktop user's
+session, using that session's actual runtime directory and bus:
+
+```sh
+gdbus call --session --dest org.freedesktop.DBus \
+  --object-path /org/freedesktop/DBus --method org.freedesktop.DBus.ListNames
+gdbus call --session --dest org.freedesktop.DBus \
+  --object-path /org/freedesktop/DBus --method org.freedesktop.DBus.ListActivatableNames
+pkg-config --modversion gstreamer-1.0 gstreamer-app-1.0 gstreamer-video-1.0 gio-unix-2.0
+```
+
+## Existing implementation reviewed
+
+- `ui/frame_pcview.py` selects PCView only on Windows and rejects Linux even
+  when enabled. Linux installers do not carry its native bundle.
+- `desktop/portal.c` creates a **RemoteDesktop** session, requests pointer and
+  keyboard devices, and selects monitors and windows (`types=3`). It is not
+  ScreenCast-only or screen-only. Its restricted fd/node and fresh-connection
+  handling are reusable.
+- `ui/frame_pc_agent.py` calls the selection a shared window or screen and
+  picks VA-API when the element is present, falling back to x264. A bounded
+  x264 slice needs explicit encoder policy and unsupported-input behavior;
+  exposing the existing Linux path alone would not meet that scope.
+- `app/main.js` starts Python with the inherited environment; it does not
+  supply a compositor, portal backend or capture permission.
+- `.github/workflows/pc-host.yml` installs native dependencies and tests
+  synthetic x264/protocol behavior with fake capture consent/input. This does
+  not establish interactive Linux desktop capture.
+- Issue #23 and its six existing comments distinguish prior synthetic
+  helper/viewer results from untested Linux desktop capture and consent.
+
+## Verification and limits
+
+`python3 -m unittest discover -s tests -p 'test_pc*.py' -v` exited **0**:
+27 tests ran successfully, with one additional native-class setup skip
+(`native PC libraries not built on this host`). Coverage includes the compiled
+C controller trace, Python adapters, grants and default-off/Windows-only gates.
+It does not prove native GStreamer capture or local-client streaming.
+
+No fake/local native stream, consent prompt, real desktop capture, Frame viewer
+run, benchmark, input or window mode was tested in this investigation. No SSH
+connection to the Frame was needed; no lock was acquired and no headset install,
+launch, stop or settings change was attempted. Issue #113 was left alone.
+No issue comments or other public messages were sent.
+
+## Concrete unblock and next slice
+
+1. Supply an interactive Linux desktop, physical or VM, with a working
+   ScreenCast portal/backend, PipeWire and accessible consent dialog. Installing
+   the portal frontend alone is insufficient. A VM can establish software
+   capture/x264 behavior while physical-host behavior remains unverified.
+2. Install the native dependencies listed in `pc-host.yml` in that environment
+   and build a local `--with-x264` bundle. Resolve x264 distribution
+   licensing/source obligations before shipping it: the current build labels
+   that option test-only and the Windows installer omits it.
+3. Implement a ScreenCast-only session with monitor-only selection, no
+   RemoteDesktop/device request, disabled input in protocol and viewer, hidden
+   window/virtual-display modes, and explicit x264 selection. Preserve the
+   default-off gate and existing Mac/Windows paths.
+4. Verify consent acceptance/refusal/cancellation, Stop/reopen, connection loss
+   and portal closure with a local client decoding actual captured content.
+   Run the shared benchmark and record results without inferring hardware or
+   physical laser behavior.
+5. Only after local capture works, acquire the shared Frame lock once and
+   follow [the headset procedure](../testing.md#headset-smoke-test) for a brief
+   viewer test. If occupied, leave the lock alone and defer device testing.
+
+These are prerequisites and proposed scope, not a ready feature. The Linux
+host request in #23 remains open.

docs/evidence/panel-discovery-2026-10-24.md

@@ -0,0 +1,65 @@
+# Panel discovery investigation, 2026-10-24
+
+Base: v0.4.16 (`040581a`). Scope: issue #73, Desktop Capture and Control.
+
+## Evidence and change
+
+Issue #73 reports SteamOS 0.4.5 with its desktop visibly running, without a
+Frame Control version or steps. The maintainer's 2026-10-12 comment identifies
+the duplicate `loadPanels` UI function fixed in 0.4.3 and requests the exact
+remaining message and SteamOS build if it persists. There is no reporter
+follow-up. At this base, the functions are distinct and the existing Node
+regression checks their uniqueness and the Desktop GET request.
+
+Read-only source inspection found a remaining diagnostic ambiguity:
+`read_props()` returns `{}` for failed/timed-out X queries and missing root
+properties. `panels()` treated that like a confirmed empty focusable-window
+list. With no detected Plasma process it claimed no panel was open; with Plasma
+it claimed SteamOS was not listing the desktop. Neither claim follows from an
+unreadable list.
+
+The change checks for the presence of `GAMESCOPE_FOCUSABLE_WINDOWS` before
+those claims. An absent list now reports unknown panel state, suggests checking
+SteamVR and retrying/Headset view, and asks for the exact message and SteamOS
+version if persistent. Missing-tool and whole-run deadline explanations retain
+precedence. No new probes, retries, timeouts, input or capture routes are added.
+
+## Real-device boundary
+
+A preliminary read-only SSH inspection returned SteamOS 0.5.6, BUILD_ID
+`20261015.6141207`, battery 99%, discharging, and X0/X1 socket names. It made
+no headset changes. The shared lock was absent at that moment.
+
+The subsequent atomic `mkdir /tmp/frame-test.lock` failed with `File exists`.
+The guarded command exited with status 3 before the session, X-property or
+panel-helper probes ran. The other task's lock was left alone. No application
+was installed, started, stopped or focused; no headset settings changed.
+
+That implementation probe was blocked by the occupied shared device. The
+coordinator later supplied a separate narrow read-only observation on SteamOS
+0.5.6, BUILD_ID `20261015.6141207`, at battery 99%, with the shared lock absent
+and both `xprop` and `xwininfo` installed:
+
+- In **Game Mode**, `DISPLAY=:0 xprop -root GAMESCOPE_FOCUSABLE_WINDOWS
+  GAMESCOPE_FOCUSED_WINDOW` returned both properties **present but empty**.
+- On `DISPLAY=:1`, both properties were reported **not found**.
+
+This observation distinguishes a confirmed empty list on `:0` from absent
+properties on `:1`. It does **not** reproduce #73's Desktop Mode report on
+SteamOS 0.4.5, and it does **not** test this PR's code on the headset. It is a
+coordinator-supplied observation, separate from the blocked implementation probe
+above; no new headset probe was run for this follow-up.
+
+Remaining limit: there is no reproduction establishing a further
+capture/discovery fix for the reported Desktop Mode/build combination. This PR
+improves a demonstrated diagnostic error; it must not close #73 as a verified
+new capture fix.
+
+## Offline verification
+
+Focused Python regressions distinguish absent, focus-only, failed/timed-out X
+queries, confirmed empty and desktop-running lists. Existing tests cover
+missing tools, alternate displays, successful discovery and the 12-second
+deadline. The production page's Node behavior test verifies that both Capture
+and Control preserve the unreadable-list advice. These use fake X/HTTP/DOM
+boundaries and do not prove real SteamOS 0.4.5 capture or physical input.

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

docs/pc-in-headset.md

@@ -107,6 +107,12 @@ The Linux adapter from #38 (desktop portal, PipeWire, VA-API) is in the tree,
 because it shares `capture.c` and the controller, and CI still builds and tests
 it. The app never offers it and the Linux installers don't include it.
 
+The [2026-10-24 lxso2 feasibility check](evidence/linux-pc-host-lxso2-2026-10-24.md)
+found no running or activatable desktop portal, no PipeWire socket and missing
+native build dependencies. Linux support remains disabled. The evidence records
+the build failure and prerequisites for a screen-only, view-only x264 slice;
+Linux capture, input and window modes have not been verified there.
+
 ## Measuring
 
 The Mac benchmark accepts the PC host:

docs/recording.md

@@ -162,16 +162,34 @@ was released, and the battery remained at 99%. The Steam source clip was kept.
 
 The inspected frame is nearly black in both Steam's source and the export, so
 this establishes file creation and faithful export, **not visible gameplay
-capture**. The literal desktop **Export** button was not clicked. Remaining
-checks include:
+capture**. On v0.4.16, the literal desktop **Export** button was also clicked
+against that retained real Steam clip in the source UI on lxso2. The job
+completed and saved `~/Videos/SteamFrame/clip_13009719723623972864_20261024_072115.mp4`;
+its 159,829 bytes and SHA-256 matched the previously decoded export exactly.
+The temporary server stopped, the shared device lock was released, and the
+headset remained in Game Mode at 99% battery. See
+[`docs/evidence/clip-gui-export-2026-10-24.json`](evidence/clip-gui-export-2026-10-24.json)
+for the narrow proof. This did not exercise the packaged desktop installer.
+
+On 2026-10-24, the exact v0.4.17 tag exported a second real Steam-saved clip
+through `frame_clips.export_clip`, the same production path used by **Export**.
+Steam listed the clip at **100.801 seconds**, with 68 chunks and no gaps. The
+copied MP4 was **100.833 seconds** by `ffprobe` and decoded completely with
+`ffmpeg`; it was not cut at 60 seconds. The test restored Steam's recording
+mode, removed its reserved title and processes, and left Game Mode active at
+100% battery. See [the long-clip evidence](evidence/clip-long-2026-10-24.json).
+This did not click **Export** in the packaged desktop app or verify visible
+gameplay quality or perceptual audio/video sync.
+
+Remaining checks include:
 
 - Perceptual audio/video sync and audible content. Frame Control's separate
   **Record** path stamps camera and audio inputs with the wall clock because
   they otherwise count from different clocks.
-- Long saved clips, trims starting partway through a Steam recording, and the
-  desktop **Export** button. One real saved clip's
-  directory layout was checked; the parser remains deliberately loose for
-  other layouts.
+- Clips longer than the 100-second test, trims starting partway through a Steam
+  recording, and the packaged desktop app's **Export** button. Two real saved
+  clips' directory layouts were checked; the parser remains deliberately loose
+  for other layouts.
 - How much x264 at 1080p30 costs the Frame while a game is running.
 - Automatic copying: that 30 seconds without a write is a safe sign Steam has
   finished saving a clip, and how a once-a-minute listing feels on the Frame.

docs/streaming.md

@@ -7,6 +7,9 @@ This covers three directions, plus input:
 - **C. iPhone → Frame**: mirror the phone inside the headset.
 - **PC VR from Linux**: [feasibility and options](linux-vr-streaming.md),
   including Valve's streaming and USB support. No Linux host tested yet.
+- **Linux desktop → Frame panels**: [PC-host feasibility on lxso2](evidence/linux-pc-host-lxso2-2026-10-24.md).
+  Blocked on missing desktop portal/PipeWire and native build dependencies;
+  Linux desktop capture remains disabled and unverified.
 - **Input**: type and point in the Frame from the Mac or iPhone.
 - **Live view and Control**: watch a panel flat and tap on it to use it.
 
@@ -285,6 +288,13 @@ How (**verified 2026-09-29**, SteamOS 0.4.1, build 20260925.6191901):
   [#73](https://github.com/saphid/frame-control/issues/73) (SteamOS 0.4.5, desktop
   open but not found). The likely cause there was the page itself: a second
   `loadPanels` (the panel switcher's) replaced the Desktop view's, fixed in #84.
+  If the `GAMESCOPE_FOCUSABLE_WINDOWS` property cannot be read, discovery now
+  reports that the panel list is unreadable and whether a panel is open is
+  unknown. A failed X connection or missing property is not evidence that the
+  desktop is closed. Check that SteamVR is running, retry or use Headset view;
+  if it persists, report the exact message and SteamOS version. The confirmed
+  empty-list advice is retained when the property is present but empty.
+  [2026-10-24 investigation and verification limits](evidence/panel-discovery-2026-10-24.md).
 - Tested from the iPhone app (Simulator): a tap on the Desktop view focused a
   text box in the panel and the text field typed into it; a trackpad move went
   exactly (+40, +25).

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/page/desk_panels.mjs

@@ -40,6 +40,15 @@ function page(answer) {
   if (!p.noPanelWhy().startsWith("The headset's desktop is running")) fail("why for capture: " + p.noPanelWhy());
   if (!p.ctrlTarget().why.startsWith("The headset's desktop is running")) fail("why for control: " + p.ctrlTarget().why);
 }
+// An unreadable list is unknown: both Capture and Control retain that distinction.
+{
+  const why = "Frame Control couldn't read gamescope's panel list, so it can't tell whether an app panel is open. " +
+    "Check that SteamVR is running in the headset, then try again or use the Headset view. " +
+    "If this persists, report your SteamOS version and this exact message.";
+  const p = page(() => ({ panels: [], focus: null, why }));
+  await p.loadPanels();
+  if (p.noPanelWhy() !== why || p.ctrlTarget().why !== why) fail("unreadable list reason lost");
+}
 // An older headset script without "why": the generic advice.
 {
   const p = page(() => ({ panels: [], focus: null }));

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/test_touch.py

@@ -355,6 +355,8 @@ class FindingPanels(unittest.TestCase):
         t.subprocess.run = lambda *a, **k: subprocess.CompletedProcess(a, 0, out, "")
         self.assertEqual(self.real_read_props(":0"), {"GAMESCOPE_FOCUSABLE_WINDOWS": [1, 0, 2, 3, 769, 4],
                                                       "GAMESCOPE_FOCUSED_WINDOW": [0]})
+        t.subprocess.run = lambda *a, **k: subprocess.CompletedProcess(a, 0, "GAMESCOPE_FOCUSABLE_WINDOWS(CARDINAL) = \n", "")
+        self.assertEqual(self.real_read_props(":0"), {"GAMESCOPE_FOCUSABLE_WINDOWS": []})
         t.subprocess.run = lambda *a, **k: subprocess.CompletedProcess(a, 0, "GAMESCOPE_FOCUSED_WINDOW:  not found.\n", "")
         self.assertEqual(self.real_read_props(":0"), {})
 
@@ -392,17 +394,52 @@ class FindingPanels(unittest.TestCase):
         self.assertIn("Headset view", out["why"])
 
     def test_desktop_running_but_not_listed(self):
+        self.props[(":0", "GAMESCOPE_FOCUSABLE_WINDOWS")] = []
         self.t.desktop_running = lambda: True
         out = self.t.panels()
         self.assertEqual(out["panels"], [])
         self.assertIn("desktop is running", out["why"])
 
     def test_nothing_open(self):
+        self.props[(":0", "GAMESCOPE_FOCUSABLE_WINDOWS")] = []
         out = self.t.panels()
         self.assertEqual(out, {"focus": None, "focus_display": None, "panels": [],
                                "why": "No app panel is open in the headset. Open the desktop or an app in "
                                       "the headset, then try again."})
 
+    def test_absent_list_is_unknown_even_when_desktop_is_running(self):
+        for desktop in (False, True):
+            with self.subTest(desktop=desktop):
+                self.t.desktop_running = lambda: desktop
+                self.t._ROOT.clear()
+                out = self.t.panels()
+                self.assertEqual(out["panels"], [])
+                self.assertIn("couldn't read gamescope's panel list", out["why"])
+                self.assertIn("can't tell whether", out["why"])
+                self.assertIn("Headset view", out["why"])
+                self.assertNotIn("No app panel is open", out["why"])
+
+    def test_focus_property_without_panel_list_is_unknown(self):
+        self.props[(":0", "GAMESCOPE_FOCUSED_WINDOW")] = [0]
+        self.assertIn("couldn't read gamescope's panel list", self.t.panels()["why"])
+
+    def test_failed_xprop_does_not_claim_no_panels_are_open(self):
+        t = self.t
+        t.read_props = self.real_read_props
+        saved = t.subprocess.run
+        self.addCleanup(setattr, t.subprocess, "run", saved)
+        for failure in ("refused", "timeout"):
+            with self.subTest(failure=failure):
+                def run(*args, **kwargs):
+                    if failure == "timeout":
+                        raise subprocess.TimeoutExpired(args[0], kwargs["timeout"])
+                    return subprocess.CompletedProcess(args[0], 1, "", "Can't open display")
+                t.subprocess.run = run
+                t._ROOT.clear()
+                out = t.panels()
+                self.assertIn("couldn't read gamescope's panel list", out["why"])
+                self.assertNotIn("No app panel is open", out["why"])
+
     def test_missing_x_tools_are_named(self):
         self.plasma_on(":0")
         self.t.shutil.which = lambda tool: None if tool == "xwininfo" else "/usr/bin/" + tool

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/frame_touch.py

@@ -271,7 +271,7 @@ def panels(limit=None):
         out["why"] = ("The headset took too long to list its panels (its X tools didn't answer in time). "
                       + ("Some may be missing. " if found else "") + "Try again, or use the Headset view.")
     elif not found:
-        out["why"] = why_none(unfound)
+        out["why"] = why_none(unfound, props)
     return out
 
 
@@ -295,13 +295,18 @@ def desktop_running():
     return False
 
 
-def why_none(listed):
+def why_none(listed, props):
     """Why panels() found nothing, in words the person at the computer can act on.
-    listed: how many of the windows gamescope lists aren't X11 windows on any display."""
+    listed: how many of the windows gamescope lists aren't X11 windows on any display.
+    props: the root properties actually read; an absent list is not an empty list."""
     missing = [tool for tool in ("xprop", "xwininfo") if not shutil.which(tool)]
     if missing:
         return (f"This SteamOS build has no {' or '.join(missing)}, which Frame Control uses to find the "
                 "headset's panels. Use the Headset view instead, and please report your SteamOS version.")
+    if "GAMESCOPE_FOCUSABLE_WINDOWS" not in props:
+        return ("Frame Control couldn't read gamescope's panel list, so it can't tell whether an app panel is open. "
+                "Check that SteamVR is running in the headset, then try again or use the Headset view. "
+                "If this persists, report your SteamOS version and this exact message.")
     if listed:
         # gamescope lists windows, but none is an X11 window on any display: a Wayland
         # window (a desktop drawn straight to gamescope, say) can't be found or captured this way.

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++;