fix: make an existing classroom converge into the Plasma appliance

A real room upgraded to 0.1.45 and came up as stock Debian Plasma with
the old Waybar across the top, mako still catching notifications, and a
lock screen on an account that has no password.

The cause was one line, and it was in the lab: the harness handed the
session under test XDG_CONFIG_DIRS by hand, so every result it had ever
produced was a result about a machine somebody had already configured.
On a machine SDDM starts the session through PAM, PAM does not read
/etc/environment.d, and Debian's own plasma-workspace env.sh then set the
variable from scratch — so the classroom's settings directory was not in
the cascade at all. No layout, no lock policy, no Kiosk restrictions.

The settings now arrive the way Plasma delivers them, through a file in
/etc/xdg/plasma-workspace/env. Around that: the look and feel is
immutable on its own key so a stale profile cannot answer for it; the
palette is composed into the package, because naming a colour scheme does
not produce one and the dark bar had been coming from a technician's
hand; the desktop reset converges another desktop's appearance state and
keeps the room's own; and classroom-migrate stops, deactivates and masks
the old shell, including the D-Bus activation that brought mako back
while the panel was down — found only by killing the panel on a migrated
machine.

device.conf loses COMPOSITOR and comes off the hyprland channel, which
would otherwise have handed the room the experiment back.

The lab stops flattering the package: it restarts the machine, lets SDDM
actually autologin, and asks a fresh install and a machine upgraded from
the Hyprland package the same sixty questions. Both answer identically,
twice, and the panel still comes back from eight SIGKILLs.

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

config/plasma/env/zz-ekklesia-classroom.sh

@@ -0,0 +1,33 @@
+# Put the classroom's settings into the session's configuration cascade.
+#
+# This is the file the migration failure turned on. Everything the room is
+# — the panel layout, the lock screen that must never appear, the idle
+# behaviour, the Kiosk restrictions — lives in /etc/ekklesia-classroom/xdg
+# and reaches Plasma only if that directory is in XDG_CONFIG_DIRS. It was
+# set in /etc/environment.d, which systemd's user manager reads. Measured
+# on a real machine and then reproduced in the lab: that is not enough.
+#
+# startplasma sources /etc/xdg/plasma-workspace/env/*.sh at session start,
+# and Debian's env.sh there sets XDG_CONFIG_DIRS from scratch when the
+# variable is empty — which it is, because SDDM starts the session through
+# PAM, and PAM does not read /etc/environment.d. startplasma then pushes
+# its own environment into the user manager, so the value from
+# /etc/environment.d was not merely bypassed, it was overwritten for every
+# user service as well. The room came up as stock Debian Plasma: kickoff,
+# a pager, a system tray, the Debian wallpaper, and a lock screen.
+#
+# So the classroom sets it where Plasma itself looks. The name sorts after
+# env.sh, so this appends to Debian's value rather than replacing it, and
+# the whole thing is a no-op if the directory is already there.
+#
+# The /etc/environment.d file stays: it covers user services that start
+# before, or without, a Plasma session.
+
+case ":${XDG_CONFIG_DIRS:-}:" in
+    *:/etc/ekklesia-classroom/xdg:*)
+        ;;
+    *)
+        XDG_CONFIG_DIRS="/etc/ekklesia-classroom/xdg:${XDG_CONFIG_DIRS:-/etc/xdg}"
+        export XDG_CONFIG_DIRS
+        ;;
+esac