Expand LinuxCNC interpreter regression coverage

wasm-port/tools/verify_vendor_sync.sh

@@ -24,6 +24,22 @@ if [[ ! -f "$MANIFEST_FILE" ]]; then
   exit 1
 fi
 
+validate_manifest_path() {
+  local src_rel="$1"
+  if [[ "$src_rel" = /* || "$src_rel" == */ || "$src_rel" == *"//"* ]]; then
+    return 1
+  fi
+
+  local component
+  local -a path_components
+  IFS=/ read -r -a path_components <<< "$src_rel"
+  for component in "${path_components[@]}"; do
+    if [[ -z "$component" || "$component" == "." || "$component" == ".." ]]; then
+      return 1
+    fi
+  done
+}
+
 mkdir -p "$BUILD_DIR"
 
 vendor_sync_fingerprint() {
@@ -65,7 +81,7 @@ while IFS= read -r src_rel; do
   [[ -z "$src_rel" ]] && continue
   [[ "${src_rel:0:1}" == "#" ]] && continue
 
-  if [[ "$src_rel" = /* || "$src_rel" == *".."* ]]; then
+  if ! validate_manifest_path "$src_rel"; then
     echo "invalid manifest path: $src_rel" >&2
     exit 1
   fi