@@ -0,0 +1,159 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * `defineStack(config, { strict: false })` refuses a malformed `actions` —
+ * top-level or an object's own — with an ADR-0112 envelope (#19799).
+ *
+ * ## What was wrong
+ *
+ * The non-strict door skips the parse and hands the normalized input straight
+ * to `mergeActionsIntoObjects`, which stable-sorts every `actions` array via
+ * `sortActionsByOrder` — `actions.some(…)` with no shape guard. A non-array
+ * `actions` (`5`, `'abc'`), top-level or on an object, raised a bare
+ * `TypeError: actions.some is not a function`, and a `null` entry one reading
+ * `order` off it — `code` and `status` both `undefined`. Any other non-object
+ * entry (`[5]`) was handed on inside a success.
+ *
+ * ## What is pinned
+ *
+ * Every such shape is refused with the strict parse's own envelope —
+ * `STACK_SCHEMA_INVALID`, `status: 422` — and the zod issue at the strict
+ * parse's own path: `['actions']` / `['actions', index]` for the top-level
+ * collection, `['objects', i, 'actions']` / `['objects', i, 'actions', index]`
+ * for an object's own. The top-level line is the one `composeStacks` step 3
+ * draws for the same key. Every refusal has its CONTROL: the same stack with
+ * `actions` authored as an array of action objects is accepted, merged and
+ * ordered.
+ */
+import { describe, it, expect } from 'vitest';
+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 call is accepted. */
+function refusal(fn: () => unknown): Envelope | null {
+  try {
+    fn();
+    return null;
+  } catch (e) {
+    return e as Envelope;
+  }
+}
+
+const manifest = { id: 'com.example.b', name: 'b', version: '1.0.0', type: 'app' as const };
+
+const obj = (name: string, extra: Record<string, unknown> = {}) => ({
+  name,
+  label: name,
+  fields: { title: { type: 'text' as const } },
+  ...extra,
+});
+
+const url = { type: 'url' as const, target: 'https://example.com' };
+const bound = { name: 'b_open', label: 'Open', ...url, objectName: 'b_item', order: 2 };
+const embedded = { name: 'b_first', label: 'First', ...url, order: 1 };
+const global = { name: 'b_home', label: 'Home', ...url };
+
+const nonStrict = (overrides: Record<string, unknown>) =>
+  defineStack({ manifest, ...overrides } as never, { strict: false });
+
+const strictParse = (overrides: Record<string, unknown>) => defineStack({ manifest, ...overrides } as never);
+
+function expectEnvelope(refused: Envelope | null, paths: PropertyKey[][], expected: 'array' | 'object'): void {
+  expect(refused).toBeInstanceOf(Error);
+  expect(refused?.code).toBe('STACK_SCHEMA_INVALID');
+  expect(refused?.status).toBe(422);
+  expect(refused?.issues?.map((issue) => issue.path)).toEqual(paths);
+  expect(refused?.issues?.every((issue) => issue.code === 'invalid_type' && issue.expected === expected)).toBe(true);
+}
+
+const nonArrays: Array<{ label: string; value: unknown }> = [
+  { label: 'a number', value: 5 },
+  { label: 'a string', value: 'abc' },
+  { label: 'null', value: null },
+  { label: 'false', value: false },
+];
+
+describe('#19799 — defineStack strict: false refuses a malformed top-level `actions` with an ADR-0112 envelope', () => {
+  for (const row of nonArrays) {
+    it(`top-level \`actions\` as ${row.label} is refused at ['actions'] — never a bare TypeError`, () => {
+      const refused = refusal(() => nonStrict({ objects: [obj('b_item')], actions: row.value }));
+      expectEnvelope(refused, [['actions']], 'array');
+      expect(refused?.message).toContain("'actions'");
+    });
+  }
+
+  it('a non-object ENTRY is refused, one issue per entry at [actions, index] — the card\'s `[null]` repro and a `[5]` that used to pass', () => {
+    const refused = refusal(() => nonStrict({ objects: [obj('b_item')], actions: [null, global, 5] }));
+    expectEnvelope(refused, [['actions', 0], ['actions', 2]], 'object');
+  });
+
+  it('the strict door answers the same path with the same code — one dialect for one authored mistake', () => {
+    expectEnvelope(refusal(() => strictParse({ actions: 5 })), [['actions']], 'array');
+    expectEnvelope(refusal(() => strictParse({ actions: [null] })), [['actions', 0]], 'object');
+  });
+});
+
+describe("#19799 — defineStack strict: false refuses a malformed object's own `actions` with the same envelope", () => {
+  for (const row of nonArrays) {
+    it(`an object's \`actions\` as ${row.label} is refused at ['objects', i, 'actions']`, () => {
+      const refused = refusal(() => nonStrict({ objects: [obj('b_other'), obj('b_item', { actions: row.value })] }));
+      expectEnvelope(refused, [['objects', 1, 'actions']], 'array');
+      expect(refused?.message).toContain("object 'b_item'");
+    });
+  }
+
+  it("a non-object entry in an object's `actions` is refused at ['objects', i, 'actions', index]", () => {
+    const refused = refusal(() => nonStrict({ objects: [obj('b_item', { actions: [embedded, null, 7] })] }));
+    expectEnvelope(refused, [['objects', 0, 'actions', 1], ['objects', 0, 'actions', 2]], 'object');
+  });
+
+  it('findings at several sites are reported in ONE refusal, top-level first, as the strict parse reports them', () => {
+    const refused = refusal(() =>
+      nonStrict({ objects: [obj('b_item', { actions: 'x' }), obj('b_two', { actions: [null] })], actions: [5] }),
+    );
+    expect(refused?.code).toBe('STACK_SCHEMA_INVALID');
+    expect(refused?.status).toBe(422);
+    expect(refused?.issues?.map((issue) => issue.path)).toEqual([
+      ['actions', 0],
+      ['objects', 0, 'actions'],
+      ['objects', 1, 'actions', 0],
+    ]);
+  });
+
+  it('the strict door answers the same paths with the same code', () => {
+    expectEnvelope(refusal(() => strictParse({ objects: [obj('b_item', { actions: 5 })] })), [['objects', 0, 'actions']], 'array');
+    expectEnvelope(
+      refusal(() => strictParse({ objects: [obj('b_item', { actions: [null] })] })),
+      [['objects', 0, 'actions', 0]],
+      'object',
+    );
+  });
+});
+
+describe('#19799 — the controls: well-formed `actions` are accepted, merged and ordered', () => {
+  it('arrays of action objects at both sites: the bound action is merged and every group is sorted by `order`', () => {
+    const stack = nonStrict({
+      objects: [obj('b_item', { actions: [embedded] })],
+      actions: [bound, global],
+    });
+    expect(stack.objects?.[0]?.actions?.map((a) => a.name)).toEqual(['b_first', 'b_open']);
+    expect(stack.actions?.map((a) => a.name)).toEqual(['b_home', 'b_open']);
+  });
+
+  it('an ABSENT `actions` at either site is not a malformed one — accepted', () => {
+    const stack = nonStrict({ objects: [obj('b_item')] });
+    expect(stack.actions).toBeUndefined();
+    expect(stack.objects?.[0]?.actions).toBeUndefined();
+  });
+
+  it('an empty `actions` array is accepted at either site', () => {
+    const stack = nonStrict({ objects: [obj('b_item', { actions: [] })], actions: [] });
+    expect(stack.actions).toEqual([]);
+    expect(stack.objects?.[0]?.actions).toEqual([]);
+  });
+});
@@ -2996,6 +2996,63 @@ function mergeActionsIntoObjects(config: ObjectStackDefinition): ObjectStackDefi
     );
   }
 
+  // [ADR-0112 · #19799] The same guard for every `actions` array this merge
+  // reads — the top-level one and each object's own — because
+  // `sortActionsByOrder` calls `.some` on it and reads `order` off each entry:
+  // a non-array raised a bare `TypeError` (`actions.some is not a function`),
+  // a `null` entry one reading `order`, and any other non-object entry was
+  // handed on inside a success. Each is refused with the strict parse's own
+  // envelope at the strict parse's own path — `['actions']` /
+  // `['actions', index]`, `['objects', i, 'actions']` /
+  // `['objects', i, 'actions', index]` — all findings in one refusal, as the
+  // parse reports them. `undefined` is the one non-array that is not
+  // malformed: the key is absent. This merge also ends `composeStacks`
+  // (step 7), which refuses a non-array top-level `actions` in its own step 3
+  // with this same code, so the message names both doors.
+  const actionsProblems: string[] = [];
+  const actionsIssues: z.core.$ZodIssue[] = [];
+  const guardActions = (prefix: readonly (string | number)[], label: string, declared: unknown): void => {
+    if (declared === undefined) return;
+    const reroot = (issue: z.core.$ZodIssue): z.core.$ZodIssue =>
+      ({ ...issue, path: [...prefix, ...issue.path] }) as z.core.$ZodIssue;
+    if (!Array.isArray(declared)) {
+      const { kind, issues } = describeNonArrayCollection('actions', declared);
+      actionsProblems.push(`${label} is ${kind}, not an array`);
+      actionsIssues.push(...issues.map(reroot));
+      return;
+    }
+    const positions = declared
+      .map((entry, index) =>
+        isRecord(entry) ? null : `#${index} (${entry === null ? 'null' : Array.isArray(entry) ? 'an array' : `a ${typeof entry}`})`,
+      )
+      .filter((position): position is string => position !== null);
+    if (positions.length === 0) return;
+    const parsed = z.array(z.looseObject({})).safeParse(declared);
+    if (!parsed.success) {
+      actionsIssues.push(
+        ...parsed.error.issues.map((issue) => reroot({ ...issue, path: ['actions', ...issue.path] } as z.core.$ZodIssue)),
+      );
+    }
+    actionsProblems.push(
+      `${label} holds ${positions.length === 1 ? 'an entry' : 'entries'} that ` +
+        `${positions.length === 1 ? 'is' : 'are'} not an object — ${positions.join(', ')}`,
+    );
+  };
+  guardActions([], "'actions'", (config as { actions?: unknown }).actions);
+  for (const [index, obj] of ((declaredObjects as Record<string, unknown>[] | undefined) ?? []).entries()) {
+    const label = typeof obj.name === 'string' ? `object '${obj.name}'` : `object #${index}`;
+    guardActions(['objects', index], `${label}'s 'actions'`, obj.actions);
+  }
+  if (actionsProblems.length > 0) {
+    throw new StackSchemaInvalidError(
+      `Stack validation failed (the bound-action merge that ends \`defineStack\` and \`composeStacks\`): ` +
+        `${actionsProblems.join('; ')}. Actions cannot be merged or ordered by \`order\` in that shape, and ` +
+        `\`strict: false\` skips validation, not this shape. Author every 'actions' as an array of action ` +
+        `definitions, or drop \`strict: false\` to have every schema check run.`,
+      actionsIssues,
+    );
+  }
+
   // Honour `order` on the preserved top-level actions regardless of objects.
   const sortedTop = config.actions ? sortActionsByOrder(config.actions) : config.actions;
   const topChanged = sortedTop !== config.actions;