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]>

lib/classroom_style.py

@@ -1,9 +1,11 @@
-"""The classroom stylesheet, resolved at the room's UI scale.
+"""The classroom's look: its measurements and its palette.
 
-The dock and the DVD control bar share this so they cannot drift apart:
-one template, one set of measurements, one look.
+The DVD control bar, Parent Call and the Presentations library all draw
+themselves, and they share this so they cannot drift apart: one set of
+measurements, one palette, one look.
 """
 
+import os
 from pathlib import Path
 
 from classroom_config import scaled
@@ -34,3 +36,96 @@ def render(scale, template=None):
         css = css.replace(f"@{token}@", str(scaled(value, scale)))
 
     return css
+
+
+# ---------------------------------------------------------- the palette
+
+def load_colours():
+    """The session's own palette, read from the colour scheme in use.
+
+    There is one set of design tokens in this classroom, and they live in
+    a Plasma colour scheme. Reading them here rather than repeating them
+    means this card follows classroom-theme light and dark without
+    knowing that either exists.
+    """
+    palette = {
+        "window": "#141c20", "view": "#0f171a", "text": "#e6edef",
+        "dim": "#93a5aa", "accent": "#4fb3a8", "on_accent": "#0e1518",
+        "negative": "#e36a6a", "neutral": "#e0b15c", "positive": "#6fcf97",
+        "line": "#25333a",
+    }
+
+    scheme = "EkklesiaDark"
+
+    for path in (
+        os.path.expanduser("~/.config/kdeglobals"),
+        "/etc/ekklesia-classroom/xdg/kdeglobals",
+        "/etc/xdg/kdeglobals",
+    ):
+        try:
+            with open(path, "r", encoding="utf-8") as handle:
+                section = None
+                for line in handle:
+                    line = line.strip()
+                    if line.startswith("["):
+                        section = line
+                    elif section and section.startswith("[General]") and \
+                            line.startswith("ColorScheme="):
+                        scheme = line.split("=", 1)[1].strip()
+                        break
+        except OSError:
+            continue
+        else:
+            if scheme:
+                break
+
+    def rgb(value):
+        parts = [part.strip() for part in value.split(",")]
+        if len(parts) != 3:
+            return None
+        try:
+            return "#%02x%02x%02x" % tuple(int(part) for part in parts)
+        except ValueError:
+            return None
+
+    try:
+        with open(f"/usr/share/color-schemes/{scheme}.colors", "r",
+                  encoding="utf-8") as handle:
+            group = None
+            for line in handle:
+                line = line.strip()
+                if line.startswith("["):
+                    group = line
+                    continue
+                if "=" not in line or group is None:
+                    continue
+                key, value = (part.strip() for part in line.split("=", 1))
+                colour = rgb(value)
+                if colour is None:
+                    continue
+                if group == "[Colors:Window]":
+                    if key == "BackgroundNormal":
+                        palette["window"] = colour
+                    elif key == "ForegroundNormal":
+                        palette["text"] = colour
+                    elif key == "ForegroundInactive":
+                        palette["dim"] = colour
+                    elif key == "ForegroundNegative":
+                        palette["negative"] = colour
+                    elif key == "ForegroundNeutral":
+                        palette["neutral"] = colour
+                    elif key == "ForegroundPositive":
+                        palette["positive"] = colour
+                    elif key == "BackgroundAlternate":
+                        palette["line"] = colour
+                elif group == "[Colors:View]" and key == "BackgroundNormal":
+                    palette["view"] = colour
+                elif group == "[Colors:Selection]":
+                    if key == "BackgroundNormal":
+                        palette["accent"] = colour
+                    elif key == "ForegroundNormal":
+                        palette["on_accent"] = colour
+    except OSError:
+        pass
+
+    return palette