Classroom_Desktop/docs/classroom-v2-experiment.md

# Classroom v2 architecture experiment

An open re-evaluation of the whole Ekklesia Classroom desktop stack, with
reliability as the first requirement. Nothing here reaches a stable, canary
or hyprland room, and nothing here changes the development host.

## Base

| | |
| --- | --- |
| branch | `experiment/classroom-v2` |
| base commit | `aadb1b881977b0eb25e1ca10e060977bed31a48f` |
| base subject | *fix: keep the system print dialog in front of the window that rendered it* |
| `VERSION` at base | `0.1.44` |

That commit is the published **stable** build, verified rather than assumed:
`repo/stable/manifest.json` names `ekklesia-classroom_0.1.44_amd64.deb` with
sha256 `7de568…81041`, and the copy in `repo/packages/` hashes to exactly
that. The branch is not built on `experiment/hyprland`; `git ls-files` on it
contains no Hyprland file.

## The answer, in one paragraph

Every user-visible failure the church reported is a piece of desktop
infrastructure the classroom wrote itself. The shell that disappeared had no
supervisor. The minimised window with no feedback exists because wlroots has
no minimise and the classroom invented one. The secondary window that fights
the browser needed a 314-line arbiter because sway tiles. The unrecognisable
browser icon was hand-drawn to match a monochrome set. Debian 13 already
ships a desktop that solves all four, so **the recommendation is Plasma 6.3
on the Debian the classroom already runs**, configured rather than written,
and it was built and tested here rather than argued for.

## The development host, as found

Recorded because it bounds what could be tested.

| | |
| --- | --- |
| OS | Debian 13 trixie (13.5), kernel 6.12.90 |
| machine | already a VM — root is `/dev/vda2`, GPU is `bochs-drm`, CPU is `QEMU Virtual CPU` |
| nested virtualisation | **none** — `/dev/kvm` does not exist |
| libvirt / qemu / VirtualBox | not installed |
| containers | Docker 26.1.5, cgroup v2 |
| resources | 6 vCPU, 11 GiB RAM, 160 GiB free |

**This session could not create a virtual machine**, so the candidate desktop
was given a systemd container instead. Nothing outside Docker was changed on
the host: no packages installed, no configuration touched, no service
altered. See *Alternate operating systems* for what still needs a real VM.

## The lab

`tools/lab/` builds a Debian 13 container with a full Plasma 6.3 desktop in
it, runs systemd as PID 1 so the session is supervised the way a real machine
supervises it, and nests the session inside a headless sway so that `grim`
can photograph it and a real pointer can be aimed at it.

```
tools/lab/lab build          # the image
tools/lab/cold-start 3       # three complete cold starts, from nothing
tools/lab/lab session        # compositor + Plasma session
tools/lab/lab shot NAME      # docs/screenshots/NAME.png
tools/lab/lab click X Y      # a real pointer press
tools/lab/kwin-script FILE   # ask KWin what it believes about a window
```

Every window measurement in this document came from `kwin-script`, not from
looking at a screenshot. Every click came through libinput.

Three lab-only deviations, recorded because they bound what was proven:

* **Software rendering.** llvmpipe throughout, with KWin nested in sway. This
  proves behaviour and layout, not performance on classroom hardware.
* **No sound card and no optical drive.** The audio policy was therefore
  tested as a pure function against the real room's reported hardware state
  rather than end to end, and DVD playback was not exercised.
* **Video did not decode.** VLC came up fullscreen at exactly 1920×1080 with
  the panel covered, which is the window-management result being tested, but
  the picture was black under software XWayland.

## What was measured

Each of these changed a decision.

### The panel gives up after three crashes

Plasma's own unit restarts a crashed `plasmashell`, but with
`StartLimitBurst=3` inside sixty seconds. Measured:

| | |
| --- | --- |
| kill 1 | back in 0.3 s |
| kill 2 | back in 0.4 s |
| kill 3 | **never came back** |

That is the production failure the church already had, reproduced on stock
Plasma. A four-line systemd drop-in
(`systemd/user/plasma-plasmashell.service.d/ekklesia-classroom.conf`) makes
the restart unconditional. Re-measured: **eight consecutive `SIGKILL`s one
second apart, back every time in about 2.4 s**, with the open application
window untouched.

This is the single most important line in the whole experiment, and it is a
supported override rather than a supervisor of our own.

### KWin already recovers, and takes nothing with it

`kill -9 kwin_wayland` twice: back in **0.1 s** each time, via
`kwin_wayland_wrapper`, with the running application still on screen and its
Wayland connection intact.

### A deleted panel rebuilds itself

`plasma-org.kde.plasma.desktop-appletsrc` was deleted and the shell
restarted. The classroom bar came back exactly as designed, from the layout
script in the look-and-feel package. So the recovery procedure for a damaged
desktop is one file removed and one service restarted — no reflash, and no
technician in the room.

### Plasma cannot show all five application states

The brief asks for closed, running, active, minimised and behind. Measured by
sampling the pixels of the indicator strip rather than by eye:

| state | indicator | icon |
| --- | --- | --- |
| closed | none — panel background `(26, 29, 32)` | full colour |
| running, behind | grey `(42, 45, 48)` | full colour |
| running, active | teal `(65, 127, 121)` | full colour |
| **minimised** | grey `(42, 45, 48)` — **identical to behind** | full colour |

Three marks for four states. Rather than write a task manager that draws a
fourth — which is exactly the kind of custom desktop code this experiment
exists to remove — **the classroom removes the state**: clicking a launcher
always means *show me this*, never *hide it*, and the window decoration has
no minimise button. There is nothing on the idle desktop a teacher could want
to see, so minimising in this room only ever loses the lesson.

A window minimised by some other route is still shown as running and comes
back with one click, so it can never be lost even then.

### A window rule cannot tell a browser from its popup

The first attempt maximised the browser with a KWin rule on `google-chrome`.
Measured: the window a lesson page opened was maximised too, because Chrome
gives both the same class — the very behaviour the current architecture
spends 314 lines preventing.

Chrome can tell them apart, so `--start-maximized` in the launcher does it.
Measured afterwards:

| | |
| --- | --- |
| main browser | `[0,0] 1920×1004` — the whole desktop above the bar |
| window the page opened | `[509,160] 902×683` — centred, the size the page asked for |
| main browser afterwards | unchanged |

The secondary window carries an ordinary title bar with a close button, so
the dock's sticky Close button has nothing left to do.

### Printing

A page's own Print button produced a **native KDE print dialog** through
`xdg-desktop-portal-kde`, `transient=true` on the browser, centred over it,
in the classroom's colours, offering only **Elmer**. Stacking is the window
manager's ordinary behaviour and needed no rule.

### An immutable colour scheme cannot be toggled

Marking `[General]` immutable in `/etc/xdg/kdeglobals` froze the palette so
hard that `classroom-theme light` changed the running session and lost the
change at the next start. Immutability now covers the Kiosk restrictions and
nothing else. Measured both ways afterwards.

### VLC calls itself `Vlc`

KWin's window matching is case sensitive, and a lower-case substring rule
matched nothing while reporting nothing. The rule is a regular expression
now.

## The architecture

| | |
| --- | --- |
| distribution | **Debian 13 trixie** — unchanged, so the `.deb` and OTA work survives |
| desktop | **KDE Plasma 6.3.6** (Debian's own packages) |
| compositor | **KWin 6.3.6**, Wayland |
| panel | **Plasma panel**, one full-width bar, built by a look-and-feel layout script |
| task feedback | **Icons-only Task Manager** |
| notifications | **Plasma's own** |
| browser | **Google Chrome**, unchanged |
| Wonder Ink | Chrome app mode, **its own profile** |
| session start | **SDDM autologin** (recommended; not yet tested — see risks) |
| lockdown | **KDE Kiosk** action restrictions |
| audio | one small classroom service, event driven |

### The bar

One continuous full-width bar, 76 px, the height the room already has.

* **Left** — Parent Call, drawn as a line mark in the accent rather than a
  colour tile, so it reads as a different kind of thing from the applications
  and is visibly not one of them.
* **Centre** — the applications: Wonder Ink, and the browser wearing
  **Chrome's own icon, in colour**. That is the direct answer to the teacher
  who asked whether the old monochrome glyph meant "the Internet".
* **Right** — network, volume, removable media, notifications, clock. Four
  applets placed directly on the bar rather than a system tray: the tray
  discovers whatever is installed and hides most of it behind an arrow, and
  in the lab it collected battery, brightness, clipboard, keyboard layout,
  camera, vaults and screen management on a machine with none of those.

The bar launches applications, shows their state, and shows a little status.
It is not the Live View, not Parent Call, and not a shell framework.

### Wonder Ink as an application

```
Wonder Ink   chrome --app=https://app.wonderink.org/ --user-data-dir=…/wonderink
Browser      chrome                                   the room's own profile
```

Its window class is `chrome-app.wonderink.org__-Default` — measured on a
running session, and the launcher's `StartupWMClass` matches it exactly, so
the panel shows one button rather than a launcher and a window side by side.

The separate profile buys something the current single-profile design cannot:
if a teacher signs into Wonder Ink through Google, that Google session is in
the Wonder Ink profile and closing the window ends it, while the church
YouTube sign-in lives in the browser's profile and is untouched. The
documented conflict in `browser.md` — that clearing `wonderink.org` leaves
the next teacher one click from the previous teacher's account — does not
arise.

The ordinary browser therefore no longer opens Wonder Ink. Its home page is
YouTube, because a second way in through that window would put a teacher's
lesson session in the room's shared profile, which is the leak the split
exists to prevent.

### Windows

KWin's ordinary behaviour, with one rule.

* Main windows fill the desktop above the bar, edge to edge, because Chrome
  is told to start maximized.
* Windows a page opens float over the main one, centred, at the size the page
  asked for, with a title bar and a close button.
* Dialogs are transient on their parent and stack correctly with no help.
* Fullscreen video covers the whole display: `[0,0] 1920×1080`, panel
  included, no rounding, no wallpaper.
* One rule, and it is `noborder` for VLC.

**The outer margin and the 10 px rounding were dropped.** Chrome squares its
own corners when maximised, so margin and rounding are the same decision, and
expressing "the screen minus 16 px" needs a rule generated per resolution at
every boot. That is glue in exchange for appearance, and the brief says
reliability wins. Full-bleed above the bar is also what every other appliance
does.

### Theme

One set of design tokens in `EkklesiaDark.colors`; the light scheme is
**generated** from it by `tools/build-light-scheme`, so a colour can only be
changed in one place. Plasma applies either to the panel, the notifications,
the decorations and every dialog at once. `classroom-theme light|dark|toggle`
is the whole switch. Accent teal `#4FB3A8`, taken from the wallpaper.

### Wallpaper

`config/wallpapers/classroom-calm.png` is a **stand-in**, generated by
`tools/build-wallpaper` in the sage/teal/blue/lavender palette with a river
leading into the picture and a quiet upper middle. The illustrated wallpaper
the church selected is not in this repository; when it arrives it replaces
that file and nothing else changes.

### Lockdown

`/etc/xdg/kdeglobals`, `[KDE Action Restrictions][$i]`. Verified by clicking,
not by reading the file: right-clicking the wallpaper produced no menu,
right-clicking the bar produced no menu, and KRunner was not running and
could not be summoned. `run_command`, `shell_access`, `logout`,
`action/lock_screen`, `action/kwin_rmb` and `plasma/plasmashell/unlockedDesktop`
all read back `false`. There is no lock screen and no session restore.

Nothing was achieved by deleting a binary. Lifting a restriction for
maintenance is one line and a session restart.

### Audio

The one place custom code is still right, because no desktop expresses this
policy. `lib/classroom_audio.py` is a pure function so it can be tested
against the room that failed rather than against a machine:

* a port that reports itself unavailable is not a candidate;
* an analog port existing is not evidence that a cable is in it;
* an explicit `AUDIO_OUTPUT=hdmi|analog` overrides everything.

`scripts/classroom-audio` follows PipeWire's own event stream — no polling —
and on every change sets the card profile, sets the default sink, and
**moves streams that are already playing**. That last step is the fix for the
teacher who had to restart the browser after changing the output.

Twelve test cases in `tests/test-classroom-audio.sh`, the real room among
them. The service is supervised the same way the panel is; measured, it came
back from four consecutive kills.

### DVD

`/usr/share/solid/actions/ekklesia-dvd.desktop` with an
`X-KDE-Solid-Predicate` for a video DVD. Plasma's device notifier offers
"Play the DVD" while a disc is in the drive and withdraws it when the disc
leaves, so a room without a drive shows nothing and no room needs
`DVD_ENABLED` edited. Nothing polls, and `classroom_optical`'s two-second
loop goes away. **Not exercised** — the lab has no optical drive.

## Custom code this deletes

Deleted on this branch, and counted rather than estimated:

| | lines | replaced by |
| --- | --- | --- |
| `scripts/classroom-dock` | 754 | the Plasma panel |
| `scripts/classroom-chrome-windows` | 314 | `--start-maximized`, and a window manager |
| `tests/test-classroom-chrome-windows.sh` | 280 | — |
| `config/dock/style.css.in` | 102 | the colour scheme |
| `scripts/classroom-notifications` | 74 | Plasma notifications |
| `config/sway/config` | 62 | `kwinrc` |
| `config/mako/config.in` | 48 | `plasmanotifyrc` |
| `config/waybar/*` | 55 | the Plasma panel |
| `config/bash_profile`, getty autologin | 6 | SDDM |
| `config/icons/browser.svg` | — | Chrome's own icon |
| **total** | **1 695** | |

Rewritten rather than deleted: `classroom-browser` (41 → 30 lines, it no
longer decides launch-or-focus-or-minimise), `classroom-scale` (sway output
scale → `kscreen-doctor`), `classroom-notify` (found the session by looking
for sway and refused to run without mako; now looks for the compositor and
the shell).

**Still present, and still sway-shaped.** `classroom-window`,
`classroom_sway.py`, `classroom_icons.py`, `classroom_style.py` and
`classroom_optical.py` are all reachable only from the DVD player and the
MQTT notifier, and they were deliberately not rewritten — see *the DVD
player* under unresolved risks. Another ~590 lines go when that is done.

Kept because they are the classroom's own subject matter: the DVD session
and CSS setup, printer setup, provisioning, MQTT, the updater, shutdown.
Added: the audio policy and its test, the theme switch, and configuration.

The package was built and its contents checked: every `/usr/local` path any
classroom command names is in it.

## Alternatives, and why they lost

**Stay on sway, add Waybar.** Cheapest migration, and it loses on the thing
that matters. wlroots has no minimise, so the invented hidden workspace
stays; sway tiles, so the 314-line window arbiter stays; there is no
window-manager decoration, so the dock's sticky Close button stays; and
Waybar is one more unsupervised process to lose. It removes none of the four
reported problems.

**Hyprland** (`experiment/hyprland`). Already measured on this repository and
already carrying two findings against it: the legacy config silently matches
nothing, and a Lua config changes the IPC language so the classroom would be
adopting a brand-new format early. For critical production UI in a room
nobody attends on a Sunday morning, that is the wrong end of the maturity
curve.

**GNOME.** Task state, a bottom bar and application pinning all need
extensions, and extensions break on GNOME updates. That is precisely the
"several fragile independently-maintained components" the brief rules out.

**Fedora KDE / Arch.** Both would supply the same Plasma. Neither supplies
anything Debian 13 does not, and both would cost the entire `.deb` and OTA
investment. Arch's rolling updates are the wrong risk for an appliance that
must survive unattended. **Changing distribution buys nothing here**, which
is the most useful negative result in this document.

**Firefox ESR / Chromium instead of Chrome.** No concrete benefit. Firefox
has no app mode, which is what makes Wonder Ink an application; Debian's
Chromium ships no Widevine. Chrome is what Wonder Ink is known to work in.

## Reliability results

| test | result |
| --- | --- |
| cold start, 3 identical runs | 16, 16, 17 s — panel, compositor and 11 applets every time |
| `plasmashell` SIGKILL ×8 at 1 s | back every time, ≈2.4 s |
| `plasmashell` on stock settings | **dead on the third kill** — fixed by the drop-in |
| `kwin_wayland` SIGKILL ×2 | back in 0.1 s, windows survived |
| audio service SIGKILL ×4 | active every time |
| panel configuration deleted | rebuilt itself from the layout script |
| right-click desktop / panel | no menu |
| KRunner | not running, not reachable |
| light ⇄ dark | persists both ways |

## Screenshots

In `docs/screenshots/`.

`v2-idle-desktop` the idle desktop · `v2-light-bar` / `v2-dark-bar` the same
bar in both themes · `state-1-closed` closed · `state-3-behind` active beside
running · `state-4-minimized` · `state-5-restored` · `v2-testpage` a
maximised browser · `v2-secondary-window` a window a page opened, floating ·
`v2-print-dialog` · `v2-notification-crop` · `v2-fullscreen` · `recover-panel`
the bar rebuilt from nothing · `lock-desktop-rmb`, `lock-panel-rmb`,
`lock-krunner` the lockdown.

## Not done, and honest about it

* **DVD end to end.** No drive in the lab.
* **Real audio hardware.** Policy tested as a function; no card to apply it to.
* **Video decode and performance.** Software rendering only.
* **SDDM.** Recommended over the current `bash_profile` `exec`, because when
  the session ends SDDM starts another one instead of leaving a teacher at a
  shell prompt. Not yet configured or tested.
* **Packaging.** `tools/build-release.sh` still installs the sway-era file
  list. The desktop is installed by `tools/lab/install-desktop`, which is the
  shape the package needs but is not the package.
* **Parent Call and Live View.** Placed in the architecture, not built. Live
  View's pin is KWin's Keep Above, which is already a title-bar button.
* **UI scale.** Plasma's own display scaling replaces `classroom-scale`; not
  exercised at 1.25 or 1.5.

## Alternate operating systems

None is required. The recommendation stays on Debian 13, which the classroom
already runs and already packages for.

If the church later wants Fedora KDE or Arch compared on real hardware, that
needs a VM this session could not create:

> **Recommended next candidate: none.**
> Debian 13 + Plasma 6.3 was actually tested, in a container, on this branch.
> A disposable VM is needed only for what a container cannot show:
> 4 vCPU, 8 GiB RAM, 60 GiB disk, a real GPU or working virtio-gpu,
> an HDMI-capable audio device, and an optical drive — to test DVD
> playback, audio switching against real hardware, SDDM autologin,
> display hotplug, and performance on classroom-class hardware.

The existing Debian classroom test VM should be kept.

## Checkpoint log

* Branch opened at `aadb1b8`; host recorded as unable to create a VM.
* Lab built; Plasma 6.3.6 running software-rendered at 1920×1080.
* Panel supervision measured, failure reproduced, drop-in written, re-measured.
* Classroom desktop written: colours, layout, window rules, Kiosk, launchers.
* Task states measured; minimise removed as a route.
* Secondary windows, print dialog, notifications, fullscreen, themes, lockdown
  all verified on a running session.
* Audio policy written with the failing room as a test.
* Cold starts repeated.

**Next**: SDDM autologin; move the file list in `tools/build-release.sh` to
the Plasma layout and build a `0.1.45~plasma1` package on its own channel;
Plasma display scaling at 1.25 and 1.5; then a real VM for DVD, audio and
performance.