fix(mosaic): reject unsafe pr merge numbers (#520)

packages/mosaic/framework/tools/git/pr-merge.sh

@@ -70,6 +70,11 @@ if [[ -z "$PR_NUMBER" ]]; then
     usage
 fi
 
+if [[ ! "$PR_NUMBER" =~ ^[0-9]+$ ]]; then
+    echo "Error: Invalid PR number '$PR_NUMBER'. PR number must contain digits only." >&2
+    exit 1
+fi
+
 if [[ "$MERGE_METHOD" != "squash" ]]; then
     echo "Error: Mosaic policy enforces squash merge only. Received '$MERGE_METHOD'." >&2
     exit 1
@@ -190,9 +195,9 @@ PY
 
 case "$PLATFORM" in
     github)
-        CMD="gh pr merge $PR_NUMBER --squash"
-        [[ "$DELETE_BRANCH" == true ]] && CMD="$CMD --delete-branch"
-        eval "$CMD"
+        cmd=(gh pr merge "$PR_NUMBER" --squash)
+        [[ "$DELETE_BRANCH" == true ]] && cmd+=(--delete-branch)
+        "${cmd[@]}"
         ;;
     gitea)
         HOST=$(get_remote_host) || {