feat: Add overlay versioning support and enforce compatibility rules

Author: thim81

package.json

@@ -49,7 +49,7 @@
     "typescript": "^5.9.3"
   },
   "engines": {
-    "node": ">=18"c
+    "node": ">=18"
   },
   "files": [
     "README.md",

test/overlay.test.js

@@ -464,6 +464,19 @@ describe('openapi-format CLI overlay tests', () => {
       expect(result.resultData.totalUsedActions).toBe(1);
       expect(result.resultData.totalUnusedActions).toBe(0);
     });
+
+    it('should treat blank overlay version as latest and allow copy', async () => {
+      const baseOAS = {info: {title: 'Sample API', version: '1.0.0'}};
+      const overlaySet = {
+        overlay: '   ',
+        actions: [{target: '$.info.title', copy: true, from: '$.info.version'}]
+      };
+
+      const result = await openapiOverlay(baseOAS, {overlaySet});
+      expect(result.data.info.title).toBe('1.0.0');
+      expect(result.resultData.totalUsedActions).toBe(1);
+      expect(result.resultData.totalUnusedActions).toBe(0);
+    });
   });
 
   describe('primitive targeting compatibility', () => {

utils/overlay.js

@@ -112,7 +112,12 @@ function isSupportedOverlayVersion(version) {
     return false;
   }
 
-  return /^1\.(0|1)\.\d+$/.test(version);
+  const normalized = version.trim();
+  if (normalized === '') {
+    return true;
+  }
+
+  return /^1\.(0|1)\.\d+$/.test(normalized);
 }
 
 function isOverlay11x(version) {