diff --git a/install/lib-backup.sh b/install/lib-backup.sh
index 530cf10..2cc379e 100644
--- a/install/lib-backup.sh
+++ b/install/lib-backup.sh
@@ -57,7 +57,10 @@ backup_file() {
   local target="$1"
   [ -f "$target" ] || return 0
   local backup="${target}.bak-$(date +%s)"
-  mv "$target" "$backup"
+  # cp -a, НЕ mv — _jq_merge_hooks ниже читает оригинал target'а после
+  # backup_file. С mv оригинал исчезает → jq не может open file →
+  # «invalid output» → rollback (gx10 fail 2026-05-18).
+  cp -a "$target" "$backup"
   BACKUP_PAIRS+=("$target|$backup")
   say "backed up existing $target to $backup"
 }