feat(store): add reactive state primitives (#311)

packages/utils/src/predicate/predicate.ts

@@ -37,12 +37,18 @@ export function isObject(value: unknown): value is object {
   return value !== null && typeof value === 'object';
 }
 
+/**
+ * Check if a value is a plain object (not a class instance like Date, Map, etc).
+ */
+export function isPlainObject(value: unknown): value is Record<string, unknown> {
+  if (!isObject(value)) return false;
+  const proto = Object.getPrototypeOf(value);
+  return proto === null || proto === Object.prototype;
+}
+
 /**
  * Check if a value is an AbortError.
  */
 export function isAbortError(value: unknown): value is Error {
-  return (
-    value instanceof Error
-    && value.name === 'AbortError'
-  );
+  return value instanceof Error && value.name === 'AbortError';
 }