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+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * The two-package COLLECTION ZOO the option-B acceptance probe boots
+ * (#15004, reader program 1/4 of the ADR-0130 D4 option-B ruling on #14512).
+ *
+ * Two ordinary `defineStack` packages — an App and a module that depends on it
+ * — carrying one member of every collection family a package can own, split
+ * across BOTH packages so no reader can pass by looking at one of them. The
+ * project is composed with `manifest: 'preserve'`, which is the only
+ * composition that produces `packages[]` (see
+ * `examples/app-multi-package/objectstack.config.ts`).
+ *
+ * ## The two shapes, and why the second one is DERIVED
+ *
+ * `additiveProject()` is what the platform emits today: every collection
+ * flattened to the top level, PLUS `packages[]` carrying the same definitions
+ * a second time.
+ *
+ * `optionBProject()` is what the ruled emitter half will emit: the flattened
+ * top level GONE, `packages[]` carrying everything exactly once.
+ *
+ * The key set that separates them is **derived from the two schemas**, never
+ * transcribed here — `ObjectStackDefinitionSchema` ∩ `AssembledPackageBodySchema`
+ * is precisely "the collections a package owns", and the complement is the
+ * seven artifact-envelope keys `packages/spec/src/assembled-package-body.test.ts`
+ * classifies. A hand-written list would be a third transcription of a set the
+ * implementation already refuses to transcribe, and — the half that matters
+ * here — a collection family added to the stack schema next month would join
+ * this probe automatically instead of silently sitting outside it. (#14877 is
+ * to publish that key set as an export; when it lands this module should read
+ * it instead of deriving it, and nothing else here changes.)
+ *
+ * ## What this fixture is NOT
+ *
+ * It is not a claim about what `composeStacks` emits. `optionBProject()` builds
+ * the option-B shape by STRIPPING the composed stack, in the fixture, precisely
+ * so the probe can measure readers against that shape while the producer stays
+ * additive — which is the ruled order (readers first, emitter last) and the
+ * reason this card touches zero production files.
+ */
+
+import {
+  AssembledPackageBodySchema,
+  ObjectStackDefinitionSchema,
+  composeStacks,
+  defineStack,
+  type ObjectStackDefinition,
+} from '@objectstack/spec';
+
+const shapeKeys = (schema: unknown): string[] =>
+  Object.keys((schema as { shape: Record<string, unknown> }).shape);
+
+/**
+ * Every top-level key that is a PACKAGE-OWNED collection — i.e. every key the
+ * assembled package body also declares. Derived, per the module header.
+ *
+ * The complement (the artifact-envelope keys `manifest`, `packages`, `api`,
+ * `server`, `i18n`, `runtimeModule`, `onEnable`) is what an option-B artifact
+ * keeps at the top level.
+ */
+export const PACKAGE_OWNED_COLLECTION_KEYS: readonly string[] = (() => {
+  const bodyKeys = new Set(shapeKeys(AssembledPackageBodySchema));
+  return shapeKeys(ObjectStackDefinitionSchema).filter((k) => bodyKeys.has(k)).sort();
+})();
+
+/** The seven keys an option-B artifact still carries at its top level. */
+export const ARTIFACT_ENVELOPE_KEYS: readonly string[] = (() => {
+  const owned = new Set(PACKAGE_OWNED_COLLECTION_KEYS);
+  return shapeKeys(ObjectStackDefinitionSchema).filter((k) => !owned.has(k)).sort();
+})();
+
+// ─── The named things every probe row asserts on ────────────────────────────
+
+export const CORE_PACKAGE_ID = 'com.example.probe.core';
+export const ORDERS_PACKAGE_ID = 'com.example.probe.orders';
+
+/** The datasource `datasourceMapping` routes the project's objects to. */
+export const PROBE_DATASOURCE = 'probe_primary';
+/** Relative to the project root — `resolve-project-database` anchors it there. */
+export const PROBE_DATASOURCE_FILE = '.objectstack/data/probe-primary.db';
+/** The `isDefault` permission set `appSecurityPluginOptions` must resolve. */
+export const PROBE_DEFAULT_PERMISSION_SET = 'probe_default_profile';
+export const PROBE_POSITION = 'probe_position';
+export const PROBE_GLOBAL_ACTION = 'probe_global_action';
+export const PROBE_OBJECT_ACTION = 'probe_object_action';
+export const PROBE_FUNCTION = 'probeSweep';
+/** What the one declared function says about itself — the half option B loses. */
+export const PROBE_FUNCTION_EFFECT = 'writes';
+export const PROBE_JOB = 'probe_nightly';
+export const PROBE_HOOK_OBJECT = 'probe_order';
+/** The object the one seed dataset targets — a dataset is named by its object. */
+export const PROBE_SEED_DATASET = 'probe_account';
+export const PROBE_LOCALE = 'en';
+
+// ─── Package 1: the App ─────────────────────────────────────────────────────
+
+const coreStack = (): ObjectStackDefinition =>
+  defineStack({
+    manifest: {
+      id: CORE_PACKAGE_ID,
+      name: 'Option-B Probe Core',
+      namespace: 'probe',
+      version: '1.0.0',
+      type: 'app',
+      description: 'The App half of the option-B acceptance probe fixture',
+    },
+    objects: [
+      {
+        name: 'probe_account',
+        label: 'Probe Account',
+        pluralLabel: 'Probe Accounts',
+        sharingModel: 'private',
+        fields: {
+          name: { name: 'name', type: 'text', label: 'Name', required: true },
+        },
+        // An OBJECT-EMBEDDED action. `collectBundleActions` walks
+        // `bundle.objects[i].actions` as well as the global list, so a reader
+        // that loses the top-level `objects` loses these too — the enumeration
+        // in #14512 comment 5523603341 measured exactly that widening.
+        actions: [
+          {
+            name: PROBE_OBJECT_ACTION,
+            label: 'Probe Object Action',
+            objectName: 'probe_account',
+            type: 'script',
+            body: { language: 'js', source: 'return { ok: true };' },
+          },
+        ],
+      },
+    ],
+    datasources: [
+      {
+        name: PROBE_DATASOURCE,
+        label: 'Probe Primary',
+        driver: 'sqlite',
+        config: { filename: PROBE_DATASOURCE_FILE },
+        active: true,
+      },
+    ],
+    datasourceMapping: [
+      { datasource: PROBE_DATASOURCE, default: true },
+    ],
+    permissions: [
+      {
+        name: PROBE_DEFAULT_PERMISSION_SET,
+        label: 'Probe Default Profile',
+        isDefault: true,
+        objects: {
+          probe_account: { allowRead: true },
+        },
+      },
+    ],
+    positions: [
+      {
+        name: PROBE_POSITION,
+        label: 'Probe Position',
+      },
+    ],
+    translations: [
+      {
+        [PROBE_LOCALE]: {
+          objects: {
+            probe_account: { label: 'Probe Account (translated)' },
+          },
+        },
+      },
+    ],
+    data: [
+      {
+        object: PROBE_SEED_DATASET,
+        mode: 'upsert',
+        externalId: 'name',
+        records: [{ name: 'Seeded Probe Account' }],
+      },
+    ],
+  });
+
+// ─── Package 2: the module that depends on it ───────────────────────────────
+
+const ordersStack = (): ObjectStackDefinition =>
+  defineStack({
+    manifest: {
+      id: ORDERS_PACKAGE_ID,
+      name: 'Option-B Probe Orders',
+      namespace: 'probe',
+      version: '1.0.0',
+      type: 'module',
+      description: 'The module half of the option-B acceptance probe fixture',
+      dependencies: { [CORE_PACKAGE_ID]: '^1.0.0' },
+    },
+    objects: [
+      {
+        name: PROBE_HOOK_OBJECT,
+        label: 'Probe Order',
+        pluralLabel: 'Probe Orders',
+        sharingModel: 'private',
+        fields: {
+          name: { name: 'name', type: 'text', label: 'Number', required: true },
+        },
+      },
+    ],
+    actions: [
+      {
+        name: PROBE_GLOBAL_ACTION,
+        label: 'Probe Global Action',
+        type: 'script',
+        body: { language: 'js', source: 'return { ok: true };' },
+      },
+    ],
+    hooks: [
+      {
+        name: 'probe_before_insert',
+        label: 'Probe Before Insert',
+        object: PROBE_HOOK_OBJECT,
+        events: ['beforeInsert'],
+        body: { language: 'js', source: 'return;' },
+      },
+    ],
+    // DECLARED, not bare: the entry carries what the function says about
+    // itself (`effect`) beside its callable. That declaration is the half an
+    // option-B artifact loses on the compiled path — `mergeRuntimeModule`
+    // re-supplies the CALLABLE from the sibling ESM module either way — so a
+    // bare `() => undefined` here would make the `functions` row report
+    // 1 -> 1 and read as coverage it does not have.
+    functions: {
+      [PROBE_FUNCTION]: { handler: () => undefined, effect: PROBE_FUNCTION_EFFECT },
+    },
+    jobs: [
+      {
+        name: PROBE_JOB,
+        label: 'Probe Nightly',
+        schedule: { type: 'cron', expression: '0 3 * * *', timezone: 'UTC' },
+        handler: PROBE_FUNCTION,
+      },
+    ],
+  });
+
+// ─── The two shapes ─────────────────────────────────────────────────────────
+
+/** Today's emitted shape: flattened top level PLUS `packages[]`. */
+export const additiveProject = (): ObjectStackDefinition =>
+  composeStacks([ordersStack(), coreStack()], { manifest: 'preserve' });
+
+/**
+ * The ruled option-B shape: `packages[]` carries every definition once, and the
+ * flattened top-level collections are gone.
+ *
+ * Built by stripping the composed project — see the module header for why the
+ * fixture, and not `composeStacks`, is what strips.
+ */
+export const optionBProject = (): ObjectStackDefinition => {
+  const composed = additiveProject() as Record<string, unknown>;
+  const out: Record<string, unknown> = {};
+  const owned = new Set(PACKAGE_OWNED_COLLECTION_KEYS);
+  for (const [key, value] of Object.entries(composed)) {
+    if (!owned.has(key)) out[key] = value;
+  }
+  return out as ObjectStackDefinition;
+};