feat: Presentations, for a teacher who downloaded tonight's session

PRESENTATIONS_ENABLED, off by default, independent of everything else. A
teacher downloads a session in ordinary Chrome and it is on the
Presentations screen a few seconds later, ready for the television. No
file manager, no import button, no Impress.

WHY NOTHING LAUNCHES A DOCUMENT APPLICATION. The brief was to use
existing presentation software, so the existing software was tried
first, on Debian 13, before any of this was designed. `soffice --show`
does start a real fullscreen slideshow — and needs XDG_SESSION_TYPE plus
a VCL plugin or it dies with "Failed to open display", shows a splash,
opened a "Tip of the Day: 1/225" dialog over the slides, and leaves the
Impress editor when the show ends. `okular --presentation` opens THREE
windows: the presentation, the ordinary document window behind it, and
an information dialog. zathura is not a presenter. pdfpc is the closest
and is another dependency with a presenter-console model. Every one of
them leaves an application on screen that can open any file on the
machine, and none of them knows there is a library to go back to.

So LibreOffice converts once, headless, at import, with no window on any
screen; poppler renders the pages; the classroom shows the pictures.
Measured: 0.34s for a ten-slide PPTX, 0.03s for its ten thumbnails,
0.10s for one slide at 1920px. That is not a new renderer — it is the
same engine Impress would have used live — and it means Escape is ours,
presenting is instant, and a PDF exported from Google Slides skips the
conversion entirely and keeps the appearance Google gave it.

THE THREE THINGS KEPT APART. The library thumbnail, the starting slide
and the retention clock are independent, because the first slide of a
Bible study session is a generic opening shared by every session and the
one that names it is usually the second. Quick Look chooses the picture;
it does not change where the slideshow starts and it does not count as
having presented anything. mark_presented() is called when a slide is
actually drawn, not when Present is pressed: an intention is not a
presentation, and a viewer that failed to start must not buy another
thirty days.

IMPORTING. The teacher's download is copied, never moved, renamed or
deleted. A file with a .crdownload beside it is still arriving. Wonder
Ink's own folder is not looked at. Two downloads of the same name are
two presentations, the second titled (2) — found in the lab, where a PDF
and a PPTX of one session both came out with the same name because the
import being named was excluded from the taken-titles set BY TITLE, and
a set holds one copy of a repeated string.

Metadata is written saying "importing" before any work, so a reboot
mid-conversion leaves a directory the next startup sweeps and imports
again. A file that cannot be converted gets a card saying so, offering
only Remove, with the teacher's download untouched.

Retention: 180 days never presented, 30 days from the last presentation,
every presentation starting the thirty over. The cleanup never touches a
presentation being shown, never leaves the library directory, and never
looks at Downloads.

The dock order is unchanged: Presentations is appended after the disc
player, so Wonder Ink, the browser and the player keep the places
teachers have been reaching for. There is a test for exactly that.

classroom-wonderink now asks feature() rather than carrying its own copy
of the default, so the panel and the command cannot disagree.

Co-Authored-By: Claude Opus 5 <[email protected]>

packaging/debian/control.template

@@ -4,7 +4,7 @@ Section: misc
 Priority: optional
 Architecture: amd64
 Maintainer: Ekklesia
-Depends: pkexec, polkit-kde-agent-1, plasma-desktop, plasma-workspace, kwin-wayland, plasma-nm, plasma-pa, plasma-widgets-addons, konsole, sddm, dbus-user-session, xwayland, fonts-dejavu, fonts-noto, network-manager, pipewire, pipewire-audio, wireplumber, pulseaudio-utils, cups, cups-client, cups-filters, foomatic-db-compressed-ppds, python3-gi, python3-gi-cairo, gir1.2-gtk-3.0, gir1.2-gtklayershell-0.1, libnotify-bin, curl, gnupg, ca-certificates, python3-paho-mqtt, python3-pyqt6.qtwebengine, python3-pyqt6
+Depends: pkexec, polkit-kde-agent-1, plasma-desktop, plasma-workspace, kwin-wayland, plasma-nm, plasma-pa, plasma-widgets-addons, konsole, sddm, dbus-user-session, xwayland, fonts-dejavu, fonts-noto, network-manager, pipewire, pipewire-audio, wireplumber, pulseaudio-utils, cups, cups-client, cups-filters, foomatic-db-compressed-ppds, python3-gi, python3-gi-cairo, gir1.2-gtk-3.0, gir1.2-gtklayershell-0.1, libnotify-bin, curl, gnupg, ca-certificates, python3-paho-mqtt, python3-pyqt6.qtwebengine, python3-pyqt6, libreoffice-impress, libreoffice-core, poppler-utils, fonts-liberation2, fonts-liberation-sans-narrow, fonts-croscore, fonts-crosextra-carlito, fonts-crosextra-caladea, fonts-urw-base35, fonts-roboto, fonts-open-sans, fonts-lato, fonts-montserrat, fonts-noto-extra
 Recommends: vlc
 Conflicts: plasma-welcome, plasma-discover, kdeconnect, kup-backup
 Description: Ekklesia managed classroom environment
@@ -36,6 +36,28 @@ Description: Ekklesia managed classroom environment
  of this build. Chrome stays exactly where it was, for the ordinary
  browser.
  .
+ libreoffice-impress and poppler-utils are Presentations, and neither is
+ ever shown to a teacher. LibreOffice runs once per import, headless,
+ with no window on any screen, to turn a PPT or PPTX into a PDF; poppler
+ turns that PDF into one picture per slide; the classroom's own library
+ shows the pictures. Measured before it was chosen: `soffice --show`
+ does start a real slideshow and then leaves the Impress editor on
+ screen when it ends, and `okular --presentation` opens its own document
+ window and an information dialog behind the slides. Neither is
+ something a teacher may be left looking at, and converting once at
+ import costs 0.34s for a ten-slide deck and nothing at all afterwards.
+ libreoffice-gtk3 is deliberately NOT here: nothing interactive runs.
+ .
+ The fonts are what a Google Slides export asks for. The metric
+ compatible families cover the Microsoft names — Liberation for Arial,
+ Times New Roman and Courier New, Carlito for Calibri, Caladea for
+ Cambria, Croscore for the same three under their Chrome OS names — and
+ Roboto, Open Sans, Lato and Montserrat are the web fonts Google Slides
+ itself offers. Every one is in Debian main and installs without a
+ question. ttf-mscorefonts-installer is deliberately absent: it is in
+ contrib, it downloads from a third party at install time and it shows
+ an EULA prompt, and an unattended classroom upgrade cannot answer one.
+ .
  The Conflicts line is deliberate. A welcome tour, a software centre and
  a phone pairing daemon are all things plasma-desktop recommends and a
  room a teacher walks into should not have.

packaging/debian/postinst

@@ -62,6 +62,13 @@ systemctl enable sddm.service >/dev/null 2>&1 || true
 systemctl --global enable ekklesia-classroom-audio.service >/dev/null 2>&1 || true
 systemctl --global enable ekklesia-classroom-desktop.service >/dev/null 2>&1 || true
 
+# The presentation watcher. Enabled on every machine and started by every
+# session, because whether it does anything is device.conf's answer, not
+# the installer's: with PRESENTATIONS_ENABLED=false — which is the
+# default, and therefore every existing classroom — it exits immediately
+# and the room never runs an importer it has no use for.
+systemctl --global enable ekklesia-classroom-presentations.service >/dev/null 2>&1 || true
+
 # The panel's disc player is decided before the display manager starts, not
 # at the same time as it. Enabled rather than started: this install has
 # just run the same command directly, below.