fix: resolve TypeScript build errors in stack.zod.ts and error-map.zod.ts

- Fix hook.object type mismatch: handle string | string[] union properly
- Fix ObjectStackRawIssue: use z.core.$ZodRawIssue to match Zod v4 types
- Fix ZodIssueMinimal.path: use PropertyKey[] to match Zod v4's $ZodIssue.path

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/spec/src/shared/error-map.zod.ts

@@ -5,21 +5,9 @@ import { suggestFieldType, formatSuggestion, findClosestMatches } from './sugges
 import { FieldType } from '../data/field.zod';
 
 /**
- * Zod v4 raw issue structure (subset used by the error map).
+ * Zod v4 raw issue type used by the error map.
  */
-export interface ObjectStackRawIssue {
-  code: string;
-  path?: (string | number)[];
-  input?: unknown;
-  values?: unknown[];
-  origin?: string;
-  minimum?: number;
-  maximum?: number;
-  expected?: string;
-  format?: string;
-  keys?: string[];
-  [key: string]: unknown;
-}
+export type ObjectStackRawIssue = z.core.$ZodRawIssue;
 
 /**
  * ObjectStack Custom Zod Error Map
@@ -142,7 +130,7 @@ export const objectStackErrorMap = (issue: ObjectStackRawIssue): { message: stri
  * Zod Issue interface (subset needed for formatting).
  */
 interface ZodIssueMinimal {
-  path: (string | number)[];
+  path: PropertyKey[];
   message: string;
   code?: string;
 }

packages/spec/src/stack.zod.ts

@@ -266,10 +266,15 @@ function validateCrossReferences(config: ObjectStackDefinition): string[] {
   // Validate hook → object references
   if (config.hooks) {
     for (const hook of config.hooks) {
-      if (hook.object && !objectNames.has(hook.object)) {
-        errors.push(
-          `Hook '${hook.name}' references object '${hook.object}' which is not defined in objects.`,
-        );
+      if (hook.object) {
+        const hookObjects = Array.isArray(hook.object) ? hook.object : [hook.object];
+        for (const obj of hookObjects) {
+          if (!objectNames.has(obj)) {
+            errors.push(
+              `Hook '${hook.name}' references object '${obj}' which is not defined in objects.`,
+            );
+          }
+        }
       }
     }
   }