Reset /var/lib/snapd in the upper layers before calling snap prepare-image

debian/changelog

@@ -6,6 +6,8 @@ livecd-rootfs (23.10.21) UNRELEASED; urgency=medium
   [ Steve Langasek ]
   * Deduplicate snaps between squashfs layers on classic:
     - Consolidate canary layers to merge 'classic' back into 'standard'
+    - Reset /var/lib/snapd in the upper layers before calling snap
+      prepare-image
 
  -- Michael Hudson-Doyle <michael.hudson@ubuntu.com>  Wed, 23 Aug 2023 11:15:26 +1200
 

live-build/functions

@@ -1230,3 +1230,14 @@ EOF
         undivert_grub "${mountpoint}"
     fi
 }
+
+# find all files under /var/lib/snapd in the target directory that aren't
+# shipped by the snapd package itself, and remove them
+reset_snapd_state() {
+    rootdir="$1"
+
+    rm -rf "$rootdir/var/lib/snapd"
+    setup_mountpoint "$rootdir"
+    chroot "$rootdir" apt-get install --reinstall -y snapd
+    teardown_mountpoint "$rootdir"
+}

live-build/ubuntu/hooks/020-canary-enhanced-sb.binary

@@ -20,6 +20,7 @@ case ${SUBPROJECT:-} in
 esac
 
 . config/binary
+. config/functions
 
 # env SNAPPY_STORE_NO_CDN=1 snap known --remote model series=16 brand-id=canonical model=ubuntu-classic-2310-amd64 > config/classic-model.model
 cat <<EOF > config/classic-model.model
@@ -134,6 +135,9 @@ channel=""
 if [ -n "${CHANNEL:-}" ]; then
     channel="--channel $CHANNEL"
 fi
+
+reset_snapd_state chroot
+
 env SNAPPY_STORE_NO_CDN=1 snap prepare-image \
     --classic config/classic-model.model $channel chroot
 mv chroot/system-seed/systems/* chroot/system-seed/systems/enhanced-secureboot-desktop

live-build/ubuntu/hooks/020-canary-live.binary

@@ -20,6 +20,7 @@ case ${SUBPROJECT:-} in
 esac
 
 . config/binary
+. config/functions
 
 # env SNAPPY_STORE_NO_CDN=1 snap known --remote model series=16 brand-id=canonical model=ubuntu-installer-classic-2310-amd64 > config/classic-model-installer.model
 cat <<EOF > config/classic-model-installer.model
@@ -130,6 +131,9 @@ channel=""
 if [ -n "${CHANNEL:-}" ]; then
     channel="--channel $CHANNEL"
 fi
+
+reset_snapd_state chroot
+
 env SNAPPY_STORE_NO_CDN=1 snap prepare-image \
     --classic config/classic-model-installer.model $channel chroot
 mv chroot/system-seed/systems/* chroot/system-seed/systems/classic-installer