fix: correct additionalProperties condition in all Zod plugin versions

- Changed from Object.keys(properties) to Object.keys(schema.properties)
- Added ZodType for circular references in v4 plugin
- Removed type === 'object' restriction for additionalProperties
- Applied consistent fixes across v3, v4, and mini plugin versions

README.md

···
-packages/openapi-ts/README.md
+packages/openapi-ts/README.md

packages/openapi-ts/src/plugins/zod/mini/plugin.ts

···
 
   if (
     schema.additionalProperties &&
-    schema.additionalProperties.type === 'object' &&
-    !Object.keys(properties).length
+    (!schema.properties || !Object.keys(schema.properties).length)
   ) {
     const zodSchema = schemaToZodSchema({
       plugin,

packages/openapi-ts/src/plugins/zod/v3/plugin.ts

···
 
   if (
     schema.additionalProperties &&
-    schema.additionalProperties.type === 'object' &&
-    !Object.keys(properties).length
+    (!schema.properties || !Object.keys(schema.properties).length)
   ) {
     const zodSchema = schemaToZodSchema({
       plugin,

packages/openapi-ts/src/plugins/zod/v4/plugin.ts

···
 
   if (
     schema.additionalProperties &&
-    schema.additionalProperties.type === 'object' &&
-    !Object.keys(properties).length
+    (!schema.properties || !Object.keys(schema.properties).length)
   ) {
     const zodSchema = schemaToZodSchema({
       plugin,
···
     if (zodSchema.hasCircularReference) {
       result.hasCircularReference = true;
     }
+
+    // Return with typeName for circular references
+    if (result.hasCircularReference) {
+      return {
+        ...result,
+        typeName: 'ZodType',
+      } as ZodSchema;
+    }
+
     return result as Omit<ZodSchema, 'typeName'>;
   }
 
···
     }),
     parameters: [ts.factory.createObjectLiteralExpression(properties, true)],
   });
+
+  // Return with typeName for circular references (AnyZodObject doesn't exist in Zod v4, use ZodType)
+  if (result.hasCircularReference) {
+    return {
+      ...result,
+      typeName: 'ZodType',
+    } as ZodSchema;
+  }
 
   return result as Omit<ZodSchema, 'typeName'>;
 };