diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 7697789bf2..2d4fe4ca8c 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -100,3 +100,10 @@ jobs:
 
       - name: Type check example apps
         run: pnpm --filter './examples/*' run typecheck
+
+      # Backward-compatibility gate: a frozen third-party-style consumer
+      # (#2035). Unlike the examples it must NOT be migrated to accommodate a
+      # spec change — a red typecheck here means the spec dropped/narrowed an
+      # export a published-spec third party already uses. See the package README.
+      - name: Type check downstream consumer contract
+        run: pnpm --filter @objectstack/downstream-contract run typecheck
diff --git a/packages/downstream-contract/README.md b/packages/downstream-contract/README.md
new file mode 100644
index 0000000000..f1df2276fa
--- /dev/null
+++ b/packages/downstream-contract/README.md
@@ -0,0 +1,45 @@
+# @objectstack/downstream-contract
+
+A **frozen, representative third-party consumer** of `@objectstack/spec`, used as a
+backward-compatibility gate.
+
+## Why this exists
+
+Every other consumer the framework tests — the example apps, `@objectstack/dogfood` —
+lives in this monorepo and **co-evolves with the spec in the same commit**. When a spec
+change would break them, the same PR just fixes them. So they can never catch a change
+that breaks a *real* third party (e.g. [hotcrm](https://github.com/objectstack-ai/hotcrm))
+that is pinned to a **published** release and authors metadata independently.
+
+This package closes that gap. It is authored exactly the way an external project does —
+importing from the package entry points, mixing the builder (`ObjectSchema.create`),
+the `defineX` factories, and **bare metadata literals** (the pattern third parties on
+older releases used, see #2035) — and then validates that metadata against the spec.
+
+## The contract (read before editing)
+
+These fixtures are **frozen**. The gate is:
+
+> A spec change that requires editing the fixtures to stay green is, by definition, a
+> **breaking change** for third parties.
+
+So if a change here turns red:
+
+- **Do not** edit the fixtures to make it pass. That hides the very break this package
+  exists to surface.
+- Treat it as a deliberate decision: either revert/adjust the spec change to stay
+  backward compatible, or — if the break is intended — bump `@objectstack/spec` to a new
+  **major** and document the migration, *then* update the fixtures in the same PR.
+
+## What it checks
+
+- `pnpm --filter @objectstack/downstream-contract typecheck` — the fixtures are typed
+  with real spec types (`ActionInput`, `ReportInput`, `PageInput`, …). A removed or
+  narrowed export fails here (the #2023 class of break).
+- `pnpm --filter @objectstack/downstream-contract test` — runs each bare-literal fixture
+  through its schema's `.parse()` and assembles everything via `defineStack` (schema +
+  cross-reference validation — the heart of `objectstack validate`).
+
+For the live counterpart, the release pipeline can additionally run hotcrm's own
+`validate && typecheck && build` against the unreleased spec; this package is the fast,
+deterministic, in-CI floor.
diff --git a/packages/downstream-contract/package.json b/packages/downstream-contract/package.json
new file mode 100644
index 0000000000..eeefcaa674
--- /dev/null
+++ b/packages/downstream-contract/package.json
@@ -0,0 +1,19 @@
+{
+  "name": "@objectstack/downstream-contract",
+  "version": "0.0.0",
+  "description": "Frozen third-party consumer fixture — a backward-compatibility gate for @objectstack/spec. Authored the way an external project on a published release authors metadata; if a spec change breaks it, that change is breaking (#2035).",
+  "license": "Apache-2.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run"
+  },
+  "dependencies": {
+    "@objectstack/spec": "workspace:*"
+  },
+  "devDependencies": {
+    "typescript": "^6.0.3",
+    "vitest": "^4.1.9"
+  }
+}
diff --git a/packages/downstream-contract/src/account.object.ts b/packages/downstream-contract/src/account.object.ts
new file mode 100644
index 0000000000..1472b65570
--- /dev/null
+++ b/packages/downstream-contract/src/account.object.ts
@@ -0,0 +1,23 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+// Builder authoring path (object/field already have a good entry point).
+import { ObjectSchema, Field } from '@objectstack/spec/data';
+
+export const Account = ObjectSchema.create({
+  name: 'dc_account',
+  label: 'Account',
+  pluralLabel: 'Accounts',
+  icon: 'building',
+  description: 'Downstream-contract account object (builder authoring path).',
+  fields: {
+    name: Field.text({ label: 'Name', required: true, searchable: true, maxLength: 255 }),
+    stage: Field.select({
+      label: 'Stage',
+      options: [
+        { label: 'Prospect', value: 'prospect', default: true },
+        { label: 'Customer', value: 'customer' },
+        { label: 'Churned', value: 'churned' },
+      ],
+    }),
+  },
+});
diff --git a/packages/downstream-contract/src/account.view.ts b/packages/downstream-contract/src/account.view.ts
new file mode 100644
index 0000000000..961b6d9eba
--- /dev/null
+++ b/packages/downstream-contract/src/account.view.ts
@@ -0,0 +1,15 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+// Existing-factory authoring path.
+import { defineView } from '@objectstack/spec/ui';
+
+const data = { provider: 'object' as const, object: 'dc_account' };
+
+export const AccountViews = defineView({
+  list: {
+    label: 'All Accounts',
+    type: 'grid',
+    data,
+    columns: [{ field: 'name' }, { field: 'stage' }],
+  },
+});
diff --git a/packages/downstream-contract/src/log-call.action.ts b/packages/downstream-contract/src/log-call.action.ts
new file mode 100644
index 0000000000..6bc38f3be6
--- /dev/null
+++ b/packages/downstream-contract/src/log-call.action.ts
@@ -0,0 +1,17 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+// FROZEN bare-literal fixture — authored WITHOUT the factory, the way a third
+// party on an older spec did (#2035). No author-time `.parse()` runs here; only
+// the contract test's schema parse validates it. DO NOT migrate this to the
+// factory — that would hide the backward-compat break this file exists to catch.
+import type { ActionInput } from '@objectstack/spec/ui';
+
+export const LogCallAction: ActionInput = {
+  name: 'dc_log_call',
+  label: 'Log Call',
+  objectName: 'dc_account',
+  type: 'script',
+  target: 'logCall',
+  locations: ['record_header'],
+  successMessage: 'Call logged.',
+};
diff --git a/packages/downstream-contract/src/modern.action.ts b/packages/downstream-contract/src/modern.action.ts
new file mode 100644
index 0000000000..12d5b2114e
--- /dev/null
+++ b/packages/downstream-contract/src/modern.action.ts
@@ -0,0 +1,13 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+// New-factory authoring path (#2035) — an updated consumer.
+import { defineAction } from '@objectstack/spec/ui';
+
+export const ArchiveAccountAction = defineAction({
+  name: 'dc_archive_account',
+  label: 'Archive',
+  objectName: 'dc_account',
+  type: 'script',
+  target: 'archiveAccount',
+  locations: ['record_header'],
+});
diff --git a/packages/downstream-contract/src/pipeline.report.ts b/packages/downstream-contract/src/pipeline.report.ts
new file mode 100644
index 0000000000..040c37dcab
--- /dev/null
+++ b/packages/downstream-contract/src/pipeline.report.ts
@@ -0,0 +1,14 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+// FROZEN bare-literal fixture (see log-call.action.ts).
+import type { ReportInput } from '@objectstack/spec/ui';
+
+export const AccountsByStageReport: ReportInput = {
+  name: 'dc_accounts_by_stage',
+  label: 'Accounts by Stage',
+  description: 'Account count grouped by stage.',
+  type: 'summary',
+  dataset: 'dc_account_metrics',
+  rows: ['stage'],
+  values: ['account_count'],
+};
diff --git a/packages/downstream-contract/src/stack.ts b/packages/downstream-contract/src/stack.ts
new file mode 100644
index 0000000000..0f5a759230
--- /dev/null
+++ b/packages/downstream-contract/src/stack.ts
@@ -0,0 +1,24 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+// Assembles the consumer's metadata exactly as an objectstack.config.ts would,
+// so the contract test exercises defineStack's schema parse + cross-reference
+// validation (the metadata core of `objectstack validate`).
+import { defineStack } from '@objectstack/spec';
+import { Account } from './account.object.js';
+import { AccountViews } from './account.view.js';
+import { LogCallAction } from './log-call.action.js';
+import { ArchiveAccountAction } from './modern.action.js';
+
+export const ContractStack = defineStack({
+  manifest: {
+    id: 'com.objectstack.downstream_contract',
+    namespace: 'dc',
+    version: '1.0.0',
+    type: 'app',
+    name: 'Downstream Contract',
+    description: 'Frozen third-party consumer gating spec backward compatibility (#2035).',
+  },
+  objects: [Account],
+  views: [AccountViews],
+  actions: [LogCallAction, ArchiveAccountAction],
+});
diff --git a/packages/downstream-contract/src/welcome.page.ts b/packages/downstream-contract/src/welcome.page.ts
new file mode 100644
index 0000000000..6dd419c130
--- /dev/null
+++ b/packages/downstream-contract/src/welcome.page.ts
@@ -0,0 +1,26 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+// FROZEN bare-literal fixture (see log-call.action.ts). Pages were one of the
+// 16 domains with no factory before #2035, so real third parties authored them
+// exactly like this.
+import type { PageInput } from '@objectstack/spec/ui';
+
+export const WelcomePage: PageInput = {
+  name: 'dc_welcome',
+  label: 'Welcome',
+  type: 'home',
+  kind: 'full',
+  template: 'default',
+  regions: [
+    {
+      name: 'main',
+      width: 'full',
+      components: [
+        {
+          type: 'page:header',
+          properties: { title: 'Welcome', subtitle: 'Downstream contract page.' },
+        },
+      ],
+    },
+  ],
+};
diff --git a/packages/downstream-contract/test/contract.test.ts b/packages/downstream-contract/test/contract.test.ts
new file mode 100644
index 0000000000..cde669ad18
--- /dev/null
+++ b/packages/downstream-contract/test/contract.test.ts
@@ -0,0 +1,25 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+import { describe, it, expect } from 'vitest';
+import { ActionSchema, ReportSchema, PageSchema } from '@objectstack/spec/ui';
+import { LogCallAction } from '../src/log-call.action.js';
+import { AccountsByStageReport } from '../src/pipeline.report.js';
+import { WelcomePage } from '../src/welcome.page.js';
+import { ContractStack } from '../src/stack.js';
+
+// FROZEN — see README. A failure means a spec change dropped or narrowed a
+// property a published-spec third party already uses. That is breaking: adjust
+// the spec or bump major; do NOT edit the fixtures to make this pass.
+describe('downstream consumer contract (#2035)', () => {
+  it('bare-literal third-party metadata still parses against the current spec', () => {
+    expect(() => ActionSchema.parse(LogCallAction)).not.toThrow();
+    expect(() => ReportSchema.parse(AccountsByStageReport)).not.toThrow();
+    expect(() => PageSchema.parse(WelcomePage)).not.toThrow();
+  });
+
+  it('assembles into a stack — schema + cross-reference validation passes', () => {
+    expect(ContractStack).toBeDefined();
+    expect(ContractStack.objects).toHaveLength(1);
+    expect(ContractStack.actions).toHaveLength(2);
+  });
+});
diff --git a/packages/downstream-contract/tsconfig.json b/packages/downstream-contract/tsconfig.json
new file mode 100644
index 0000000000..2cf6eda84d
--- /dev/null
+++ b/packages/downstream-contract/tsconfig.json
@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "strict": true,
+    "esModuleInterop": true,
+    "forceConsistentCasingInFileNames": true,
+    "skipLibCheck": true,
+    "noEmit": true,
+    "rootDir": "."
+  },
+  "include": ["src/**/*", "test/**/*"]
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 40a496ed9f..ffaccc6624 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -856,6 +856,19 @@ importers:
         specifier: ^4.1.9
         version: 4.1.9(@opentelemetry/api@1.9.1)(@types/node@25.9.3)(@vitest/coverage-v8@4.1.9)(happy-dom@20.10.2)(msw@2.14.6(@types/node@25.9.3)(typescript@6.0.3))(vite@8.0.16(@types/node@25.9.3)(esbuild@0.28.1)(jiti@2.7.0)(tsx@4.22.4)(yaml@2.9.0))
 
+  packages/downstream-contract:
+    dependencies:
+      '@objectstack/spec':
+        specifier: workspace:*
+        version: link:../spec
+    devDependencies:
+      typescript:
+        specifier: ^6.0.3
+        version: 6.0.3
+      vitest:
+        specifier: ^4.1.9
+        version: 4.1.9(@opentelemetry/api@1.9.1)(@types/node@25.9.3)(@vitest/coverage-v8@4.1.9)(happy-dom@20.10.2)(msw@2.14.6(@types/node@25.9.3)(typescript@6.0.3))(vite@8.0.16(@types/node@25.9.3)(esbuild@0.28.1)(jiti@2.7.0)(tsx@4.22.4)(yaml@2.9.0))
+
   packages/formula:
     dependencies:
       '@marcbachmann/cel-js':