Skip mount points during backup and clean install

Prevent accidental deletion or backup of mount points:
- In create_backup(), skip paths that are mount points with a warning
- In _deploy_source_tarball(), _deploy_unpacked_archive(), and fetch_and_deploy_from_url(), use find with mountpoint pruning to avoid deleting mount point directories during CLEAN_INSTALL

misc/tools.func

@@ -1336,6 +1336,10 @@ create_backup() {
       msg_warn "Skipping backup of '${path}' (not found)"
       continue
     fi
+    if mountpoint -q "$path" 2>/dev/null; then
+      msg_warn "Skipping backup of '${path}' (is a mount point)"
+      continue
+    fi
     dest="${store}/files${path}"
     if ! mkdir -p "$(dirname "$dest")" || ! cp -a "$path" "$dest"; then
       msg_error "Backup of '${path}' failed - aborting update"
@@ -2538,7 +2542,7 @@ _deploy_source_tarball() {
 
   mkdir -p "$target"
   if [[ "${CLEAN_INSTALL:-0}" == "1" ]]; then
-    find "${target:?}" -mindepth 1 -delete
+    find "${target:?}" -mindepth 1 \( -type d -exec mountpoint -q {} \; -prune \) -o -delete
   fi
 
   tar --no-same-owner -xzf "$tarball" -C "$workdir" || {
@@ -2627,7 +2631,7 @@ _deploy_unpacked_archive() {
   # was truncated, the archive was unreadable, or it unpacked to nothing.
   mkdir -p "$target"
   if [[ "${CLEAN_INSTALL:-0}" == "1" ]]; then
-    find "${target:?}" -mindepth 1 -delete
+    find "${target:?}" -mindepth 1 \( -type d -exec mountpoint -q {} \; -prune \) -o -delete
   fi
 
   if ! cp -r "$source_dir"/* "$target/"; then
@@ -9368,7 +9372,7 @@ fetch_and_deploy_from_url() {
   mkdir -p "$directory"
 
   if [[ "${CLEAN_INSTALL:-0}" == "1" ]]; then
-    find "${directory:?}" -mindepth 1 -delete
+    find "${directory:?}" -mindepth 1 \( -type d -exec mountpoint -q {} \; -prune \) -o -delete
   fi
 
   local unpack_tmp