build: check for unindexed firmware deltas

diff --git a/release/scripts/checkfwsvr.sh b/release/scripts/checkfwsvr.sh
index 0b447ad..acb9612 100755
--- a/release/scripts/checkfwsvr.sh
+++ b/release/scripts/checkfwsvr.sh
@@ -2,6 +2,7 @@
 
 LOCAL_DIR="${1:-fwsvr_mirror}"
 MISSING_LOG="missing.log"
+EXTRA_LOG="extra.log"
 GCLOUD_BUCKET="gs://jadefw.blockstream.com/bin"
 HWDIRS="jade jade1.1 jade2.0 jadedev jade1.1dev jade2.0dev"
 
@@ -29,7 +30,7 @@ gcloud storage rsync ${GCLOUD_BUCKET} ${LOCAL_DIR} --recursive --delete-unmatche
 rm -f ${LOCAL_DIR}/_.gstmp
 
 echo "Checking firmware server files, hashes and indices"
-rm -f "${MISSING_LOG}"
+rm -f "${MISSING_LOG}" "${EXTRA_LOG}"
 
 function get_uncompressed_hash() {
     # We add a gzip header to allow gzip to decompress the zlib data
@@ -40,6 +41,7 @@ function get_uncompressed_hash() {
 for hwdir in ${HWDIRS}; do
     for index_name in index.json LATEST BETA PREVIOUS; do
         index_file="${LOCAL_DIR}/${hwdir}/${index_name}"
+        delta_file_names=""
         if [ ! -f "${index_file}" ]; then
             echo "Missing Index: ${index_file}" >> "${MISSING_LOG}"
             fw_file_names=""
@@ -47,6 +49,8 @@ for hwdir in ${HWDIRS}; do
             if [ "${index_name}" == index.json ]; then
                 # jq filter: <roots>/<release types>/<fw types>/<filename>
                 fw_file_names=$(jq -r ".[] | .[] | .[] | .filename" "${index_file}")
+                delta_file_names=$(echo ${fw_file_names} | tr ' ' '\n' | \
+                    grep "^deltas/" | sed 's/^deltas\///g' | sort | uniq)
             else
                 fw_file_names=$(cat "${index_file}")
             fi
@@ -71,14 +75,33 @@ for hwdir in ${HWDIRS}; do
                     ;;
             esac
         done
+
+        if [ -n "${delta_file_names}" ]; then
+            # Find delta files present in the bucket but not in the index
+            delta_files=$(ls ${LOCAL_DIR}/${hwdir}/deltas | sort | uniq)
+            diffs=$(diff <(printf "%s\n" "${delta_files}") \
+                <(printf "%s\n" "${delta_file_names}") \
+                | grep '^< ' | sed 's/^< /rm -f /g')
+            if [ -n "${diffs}" ]; then
+                echo "pushd ${LOCAL_DIR}/${hwdir}/deltas" >> "${EXTRA_LOG}"
+                printf "%s\n" "${diffs}" >> "${EXTRA_LOG}"
+                echo "popd" >> "${EXTRA_LOG}"
+            fi
+        fi
     done
 done
 
-# TODO: find files that are present but not listed in the indices
+# TODO: find firmware files that are present but not listed in index.jon
 
 if [ -f "${MISSING_LOG}" ]; then
+  echo "ERROR: Missing files:"
   cat "${MISSING_LOG}"
   exit 1
 fi
+if [ -f "${EXTRA_LOG}" ]; then
+  echo "ERROR: Extra files. remove with:"
+  cat "${EXTRA_LOG}"
+  exit 1
+fi
 echo "ALL GOOD!"
 exit 0