feat: take the last of sway out of the classroom

The DVD player was the only thing still speaking a compositor the room
no longer runs. It asked sway's tree whether VLC's window had really
gone fullscreen, because VLC reports playing while its window is still
the black startup one the loading cover exists to hide.

VLC's own status was measured as a replacement and is not one: it
reports fullscreen true in the same 250ms poll as playing, because the
flag is the option it was started with and not a report about its
window. So the cover is held for a floor and capped by the deadline that
was already there, and the compositor is not asked anything.

Focus-or-launch went the same way. The session already takes an
exclusive lock, so a second one cannot start, and bringing an existing
one to the front is the panel's job.

classroom-window, classroom_sway and classroom_chrome are gone with it —
the last of them was reachable from nothing at all.

DVD also moves out of the status row, where it sat beside the clock as
though a disc were a machine reading. It is an application: it is in the
row with Wonder Ink and the browser, and classroom-provision removes it
from the layout on a machine with no optical drive, which retires
DVD_ENABLED. A computer that moves between rooms takes its drive with
it; nobody remembers to edit a file when it does.

The panel is rebuilt from the package at every login now. Plasma keeps
whatever panel it first built, so an update could change the bar in the
package and never change it in a room — measured, with an icon that
outlived the file it came from. Editing the live panel configuration was
tried instead and destroyed the panel, because the shell owns that file.
Removing it before the shell starts is safe and makes the desktop
stateless.

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

scripts/classroom-desktop-reset

@@ -0,0 +1,32 @@
+#!/bin/bash
+set -euo pipefail
+
+# Make the panel come from the package, every time.
+#
+# Plasma builds the panel from the classroom's layout script whenever it
+# starts with no panel configuration, and keeps whatever it built after
+# that. That means an update could change the bar in the package and
+# never change it in a room — which is exactly what happened with an icon
+# that outlived the file it came from.
+#
+# So the configuration is removed before the shell starts and the bar is
+# rebuilt from the layout at every login. The desktop becomes stateless:
+# there is nothing in a teacher's home that an update cannot reach, and a
+# panel damaged somehow is repaired by the next login rather than by a
+# technician.
+#
+# Nothing is lost by this. The panel is immutable to teachers by Kiosk
+# policy, so there is never anything of theirs in that file.
+
+CONFIG="${XDG_CONFIG_HOME:-$HOME/.config}/plasma-org.kde.plasma.desktop-appletsrc"
+
+if [[ -e "$CONFIG" ]]; then
+    rm -f "$CONFIG"
+    echo "classroom-desktop-reset: panel will be rebuilt from the layout"
+else
+    echo "classroom-desktop-reset: no panel configuration to clear"
+fi
+
+# The icon cache remembers a name it once failed to find, which outlives
+# the package that later supplies it.
+rm -f "${XDG_CACHE_HOME:-$HOME/.cache}/icon-cache.kcache" 2>/dev/null || true