@@ -0,0 +1,26 @@
+---
+'@objectstack/spec': minor
+---
+
+fix(spec): strict `defineStack` refuses a `Set`, `Map` or other non-plain object for a map-form collection key instead of accepting it as an empty collection
+
+**BREAKING** — `defineStack` (strict, the default) now refuses a class of input it used to accept with every authored entry silently missing.
+
+`normalizeMetadataCollection` turns the map form of a collection (`permissions: { rep: { … } }`) into an array before the schema parse. It read any `typeof 'object'` value as that map form, so a `Set`, a `Map` or a `Date` went through `Object.entries`, which yields `[]` for them. The parse then saw a valid empty array: `defineStack({ manifest, permissions: new Set([{ name: 'rep', … }]) })` was accepted with `permissions: []` — the author's grants gone, no error, no warning. This reached every map-form key (every entry of `MAP_SUPPORTED_FIELDS`: `objects`, `apps`, `permissions`, `flows`, `agents`, …).
+
+| the key's value | before | after |
+| :--- | :--- | :--- |
+| a `Set`, a `Map`, a `Date` | accepted, the collection is `[]` | refused, `STACK_SCHEMA_INVALID`, `status: 422`, zod issue at the key (`expected: 'array'`) |
+| a class instance | read as a map of its own fields | refused the same way |
+| an object literal, `Object.create(null)`, a plain object from another realm | normalized (key → `name`) | unchanged |
+| an array | passed through | unchanged |
+
+Only a plain object is the map form; every other value reaches the parse unchanged and is refused there, at the key where it was written. `normalizeMetadataCollection`, `normalizeStackInput` and `normalizePluginMetadata` (public `@objectstack/spec` exports) now return such a value unchanged instead of `[]`.
+
+The one-line fix: author the key as an array (`[...set]`, `[...map.values()]`) or as a plain-object map (`Object.fromEntries(map)`).
+
+No code is added to the ADR-0112 ledger and no export changes: the refusal is the strict parse's existing `STACK_SCHEMA_INVALID`.
+
+<!-- adr-0087: not-required (no-migration-prescription) Nothing authorable moves: no spec key, Zod schema, export, config field or stored metadata shape is added, removed, renamed or re-spelled. A Set, Map or class instance is not a serializable metadata document, so no stored or authored source file carries one and objectstack migrate meta has nothing to rewrite; what narrows is the normalizer's reading of in-memory values that the map form never declared. -->
+
+Clause-②: no (narrowing)
@@ -0,0 +1,111 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * `normalizeMetadataCollection` reads ONLY a plain object as the map form.
+ *
+ * ## What was wrong
+ *
+ * The map-form branch tested `typeof value === 'object'`, so a `Set`, a `Map`
+ * or a `Date` was read as a map too. `Object.entries` of any of them is `[]`,
+ * and normalization runs before the schema parse, so the strict `defineStack`
+ * door saw a valid empty array and ACCEPTED the stack with every authored
+ * entry (e.g. its permission-set grants) gone.
+ *
+ * ## What is pinned
+ *
+ * A composed artifact is complete or it is refused. For every key that accepts
+ * the map form (derived from `MAP_SUPPORTED_FIELDS`, never transcribed), a
+ * non-plain object reaches the strict parse unchanged and is refused with the
+ * ordinary strict envelope: `STACK_SCHEMA_INVALID`, `status: 422`, a zod issue
+ * rooted at the key expecting an array. The controls: the same key authored as
+ * a plain-object map — a literal, a null-prototype object, and a plain object
+ * from another realm — is still normalized.
+ */
+import { describe, it, expect } from 'vitest';
+import { runInNewContext } from 'node:vm';
+import { normalizeMetadataCollection, MAP_SUPPORTED_FIELDS } from './metadata-collection.zod';
+import { defineStack } from '../stack.zod';
+
+type Envelope = Error & {
+  code?: string;
+  status?: number;
+  issues?: ReadonlyArray<{ code?: string; path?: readonly PropertyKey[]; expected?: string }>;
+};
+
+/** The thrown value, or `null` when the stack is accepted. */
+function refusal(fn: () => unknown): Envelope | null {
+  try {
+    fn();
+    return null;
+  } catch (e) {
+    return e as Envelope;
+  }
+}
+
+const manifest = { id: 'com.example.a', name: 'a', version: '1.0.0', type: 'app' as const };
+
+class Holder {
+  rep = { label: 'Rep' };
+}
+
+const NON_PLAIN: ReadonlyArray<readonly [string, () => unknown]> = [
+  ['a Set', () => new Set([{ name: 'rep', label: 'Rep' }])],
+  ['a Map', () => new Map([['rep', { label: 'Rep' }]])],
+  ['a Date', () => new Date(0)],
+  ['a class instance', () => new Holder()],
+];
+
+describe('normalizeMetadataCollection — only a plain object is the map form', () => {
+  for (const [label, make] of NON_PLAIN) {
+    it(`${label} is returned unchanged, never read as an empty map`, () => {
+      const value = make();
+      expect(normalizeMetadataCollection(value)).toBe(value);
+    });
+  }
+
+  it('control: an object literal is normalized with key → name', () => {
+    expect(normalizeMetadataCollection({ rep: { label: 'Rep' } })).toEqual([{ name: 'rep', label: 'Rep' }]);
+  });
+
+  it('control: a null-prototype object is normalized with key → name', () => {
+    const map = Object.assign(Object.create(null), { rep: { label: 'Rep' } });
+    expect(normalizeMetadataCollection(map)).toEqual([{ name: 'rep', label: 'Rep' }]);
+  });
+
+  it('control: a plain object from another realm is normalized with key → name', () => {
+    const map = runInNewContext('({ rep: { label: "Rep" } })');
+    expect(Object.getPrototypeOf(map)).not.toBe(Object.prototype);
+    expect(normalizeMetadataCollection(map)).toEqual([{ name: 'rep', label: 'Rep' }]);
+  });
+});
+
+describe('strict defineStack refuses a non-plain object for a map-form collection key', () => {
+  it('covers every map-form key the normalizer declares (the list is the census)', () => {
+    expect(MAP_SUPPORTED_FIELDS).toContain('permissions');
+    expect(MAP_SUPPORTED_FIELDS.length).toBeGreaterThanOrEqual(20);
+  });
+
+  for (const key of MAP_SUPPORTED_FIELDS) {
+    for (const [label, make] of NON_PLAIN) {
+      it(`'${key}': ${label} is refused with STACK_SCHEMA_INVALID / 422 at the key — never accepted as []`, () => {
+        const err = refusal(() => defineStack({ manifest, [key]: make() } as never));
+        expect(err, `'${key}' given ${label} was accepted`).not.toBeNull();
+        expect(err!.code).toBe('STACK_SCHEMA_INVALID');
+        expect(err!.status).toBe(422);
+        expect(err!.issues).toEqual(
+          expect.arrayContaining([
+            expect.objectContaining({ code: 'invalid_type', path: [key], expected: 'array' }),
+          ]),
+        );
+      });
+    }
+  }
+
+  it("control: 'permissions' authored as a plain-object map is accepted with its entry", () => {
+    const stack = defineStack({
+      manifest,
+      permissions: { rep: { label: 'Rep', objects: {} } },
+    } as never);
+    expect(stack.permissions?.map((p) => p.name)).toEqual(['rep']);
+  });
+});
@@ -114,11 +114,26 @@ export {
   singularToPlural,
 } from '../meta-spelling/manifest-collection-spelling.js';
 
+/**
+ * Whether `value` is a plain object — a `{ … }` literal, `Object.create(null)`,
+ * or a plain object from another realm (a `vm` context): its prototype is
+ * `null`, or a prototype whose own prototype is `null` (that realm's
+ * `Object.prototype`). A `Set`, `Map`, `Date`, array or class instance is not.
+ */
+function isPlainObject(value: unknown): value is Record<string, unknown> {
+  if (value === null || typeof value !== 'object') return false;
+  const proto: unknown = Object.getPrototypeOf(value);
+  return proto === null || Object.getPrototypeOf(proto) === null;
+}
+
 /**
  * Normalize a single metadata collection value from map format to array format.
  * If the input is already an array (or nullish), it is returned unchanged.
  * If the input is a plain object (map), it is converted to an array where
  * each key is injected as the `name` field of the corresponding item.
+ * Any other value — including a non-plain object such as a `Set` or `Map` — is
+ * returned unchanged, so schema validation refuses it rather than this
+ * function reading it as an empty map.
  * 
  * **Precedence:** If an item already has a `name` property, it is preserved
  * (the map key is only used as a fallback).
@@ -148,8 +163,14 @@ export function normalizeMetadataCollection(value: unknown, keyField = 'name'):
   // Nullish or already an array — pass through
   if (value == null || Array.isArray(value)) return value;
 
-  // Plain object — treat as map and convert to array
-  if (typeof value === 'object') {
+  // Plain object — treat as map and convert to array. ONLY a plain object: a
+  // `Set`, `Map`, `Date` or class instance is `typeof 'object'` too, and
+  // `Object.entries` reads its own enumerable string keys — `[]` for a `Set` or
+  // a `Map` — so treating it as the map form would hand the parse a valid empty
+  // array and drop every authored entry before any schema saw it. A non-plain
+  // object falls through unchanged so the strict parse refuses it as a
+  // non-array at the key, where it was written.
+  if (isPlainObject(value)) {
     return Object.entries(value as Record<string, unknown>).map(([key, item]) => {
       if (item && typeof item === 'object' && !Array.isArray(item)) {
         const obj = item as Record<string, unknown>;