diff --git a/tools/lab/dirty-upgrade b/tools/lab/dirty-upgrade
index be5eb34..8c79c96 100755
--- a/tools/lab/dirty-upgrade
+++ b/tools/lab/dirty-upgrade
@@ -13,6 +13,8 @@
 #   tools/lab/dirty-upgrade [NEW.deb] [OLD.deb]
 #   CHECK_ARGS=--restart tools/lab/dirty-upgrade   ask twice, either side
 #                                                  of a logout
+#   tools/lab/dirty-upgrade NEW.deb dist/ekklesia-classroom_0.2.2_amd64.deb
+#                                  the day the desktops move from 0.2.2
 #
 # The container is restarted between the install and the session, because
 # a room takes its upgrade and reboots.
@@ -38,13 +40,30 @@ docker exec "$NAME" sh -c '
     # backports for Hyprland. The lab is not testing that.
     systemctl mask ekklesia-classroom-provision.service >/dev/null 2>&1'
 
+# Which version is installed, fully configured, or the rehearsal stops.
+# Every step below is a question about one particular release, and a
+# step that quietly left the machine on another one answers for the
+# wrong release — which is how the 0.2.2 rehearsal once passed on 0.2.2.
+require_installed() {
+    local want got
+    want=$(dpkg-deb --field "$1" Version)
+    got=$(docker exec "$NAME" dpkg-query -W -f='${Version} ${db:Status-Abbrev}' ekklesia-classroom 2>/dev/null || true)
+    echo "  installed: $got"
+
+    if [[ "$got" != "$want ii " ]]; then
+        echo "  $(basename "$1") DID NOT INSTALL: [$got], wanted [$want ii]" >&2
+        echo "  Nothing after this would be a question about $want." >&2
+        exit 1
+    fi
+}
+
 step "the old classroom: $(basename "$OLD")"
+# With apt, the way a room installs anything, so an old package's own
+# dependencies are resolved rather than forced.
 docker exec "$NAME" sh -c "
-    DEBIAN_FRONTEND=noninteractive dpkg -i '/srv/classroom/${OLD#$ROOT/}' >/dev/null 2>&1
-    DEBIAN_FRONTEND=noninteractive apt-get -y -qq -f install >/dev/null 2>&1
-    DEBIAN_FRONTEND=noninteractive dpkg --configure ekklesia-classroom >/dev/null 2>&1
+    DEBIAN_FRONTEND=noninteractive apt-get install -y -qq '/srv/classroom/${OLD#$ROOT/}' >/dev/null 2>&1
     true" || true
-docker exec "$NAME" dpkg-query -W -f='  installed: ${Version}\n' ekklesia-classroom
+require_installed "$OLD"
 
 step "and everything a used machine accumulates"
 docker exec -i "$NAME" bash <<'DIRT'
@@ -164,14 +183,16 @@ DIRT
 step "the new classroom: $(basename "$NEW")"
 docker exec "$NAME" sh -c '
     systemctl unmask ekklesia-classroom-provision.service >/dev/null 2>&1 || true'
+# The way ekklesia-classroom-update installs it: apt, not dpkg. The
+# package conflicts with khelpcenter since 0.2.6.2, and dpkg -i refuses a
+# conflict where apt resolves it — so from 0.2.2 this step used to leave
+# the machine on 0.2.2 and every check below was asked of the old release.
 docker exec "$NAME" sh -c "
-    DEBIAN_FRONTEND=noninteractive dpkg -i '/srv/classroom/${NEW#$ROOT/}' 2>&1 \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y '/srv/classroom/${NEW#$ROOT/}' 2>&1 \
         | grep -E '^\[classroom-migrate\]' || true
-    DEBIAN_FRONTEND=noninteractive apt-get -y -qq -f install >/dev/null 2>&1
-    DEBIAN_FRONTEND=noninteractive dpkg --configure ekklesia-classroom >/dev/null 2>&1
     rm -f /usr/sbin/policy-rc.d
     true" || true
-docker exec "$NAME" dpkg-query -W -f='  installed: ${Version} ${db:Status-Abbrev}\n' ekklesia-classroom
+require_installed "$NEW"
 
 step "and the room reboots"
 "$LAB" reboot
@@ -188,8 +209,9 @@ step "and again, installed a second time over itself"
 # An update that changes nothing must change nothing. The migration runs
 # again here, over a machine that is already converged.
 docker exec "$NAME" sh -c "
-    DEBIAN_FRONTEND=noninteractive dpkg -i '/srv/classroom/${NEW#$ROOT/}' >/dev/null 2>&1
+    DEBIAN_FRONTEND=noninteractive apt-get install --reinstall -y -qq '/srv/classroom/${NEW#$ROOT/}' >/dev/null 2>&1
     true" || true
+require_installed "$NEW"
 before=$(docker exec "$NAME" sh -c 'cat /etc/ekklesia-classroom/device.conf | sha256sum')
 "$LAB" plasma-down >/dev/null
 "$LAB" plasma-up >/dev/null
@@ -230,6 +252,14 @@ fi
 theme dark >/dev/null
 echo "  back to $(theme show)"
 
+step "and every desktop has the classroom's wallpaper, however it was made"
+# Tiny Pebbles, 0.2.2 -> 0.2.6.4: a desktop Plasma made after the layout
+# had run came up with Plasma's own wallpaper, and nothing here noticed,
+# because every session this rehearsal started had its screen from the
+# beginning. This makes Plasma build one by itself, and puts Tiny
+# Pebbles' own file in front of a shell restart.
+"$ROOT/tools/lab/wallpaper-check" || converged=1
+
 step "and it still recovers"
 "$ROOT/tools/lab/recovery-check" || converged=1
 
diff --git a/tools/validate-trixie-release.sh b/tools/validate-trixie-release.sh
index 91397ff..b4ef29f 100755
--- a/tools/validate-trixie-release.sh
+++ b/tools/validate-trixie-release.sh
@@ -117,6 +117,13 @@ CUSTOM_SETTING=preserve-me-too
 CONFIG
     sed -i "s/@CHANNEL@/${channel}/" /etc/ekklesia-classroom/device.conf
     previous_version="$(dpkg-query -W -f='${Version}' ekklesia-classroom)"
+
+    # The release this is an upgrade FROM, proven rather than assumed: an
+    # install that silently did not happen makes every check below a
+    # check of a fresh install instead.
+    [[ "$previous_version" == "$(dpkg-deb --field "$previous" Version)" ]]
+    [[ "$(dpkg-query -W -f='${db:Status-Abbrev}' ekklesia-classroom)" == "ii " ]]
+    echo "installed the previous release, ekklesia-classroom $previous_version"
 fi
 
 run_logged candidate-install 1200 apt-get install -y -qq /packages/candidate.deb
@@ -130,6 +137,7 @@ run_logged candidate-install 1200 apt-get install -y -qq /packages/candidate.deb
 # for ever.
 candidate_version="$(dpkg-deb --field /packages/candidate.deb Version)"
 [[ "$(dpkg-query -W -f='${Version}' ekklesia-classroom)" == "$candidate_version" ]]
+[[ "$(dpkg-query -W -f='${db:Status-Abbrev}' ekklesia-classroom)" == "ii " ]]
 [[ "$(cat /usr/local/lib/ekklesia-classroom/VERSION)" == "$candidate_version" ]]
 echo "installed ekklesia-classroom $candidate_version${previous_version:+ over $previous_version}"
 
@@ -584,6 +592,8 @@ APPLETS
 
     run_logged candidate-reinstall 900 \
         apt-get install --reinstall -y -qq /packages/candidate.deb
+    [[ "$(dpkg-query -W -f='${Version} ${db:Status-Abbrev}' ekklesia-classroom)" \
+        == "$candidate_version ii " ]]
 
     # An install that changes nothing must change nothing.
     for setting in LIVE_ENABLED AUDIO_OUTPUT UI_SCALE; do