diff --git a/packages/runtime/src/sharing-rule-declared-name.data-door.pin.test.ts b/packages/runtime/src/sharing-rule-declared-name.data-door.pin.test.ts
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+++ b/packages/runtime/src/sharing-rule-declared-name.data-door.pin.test.ts
@@ -0,0 +1,221 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [ADR-0131 D6 regime C] The generic `/data` door refuses a `sys_sharing_rule`
+ * row that takes a declared rule's name, over HTTP, in the ADR-0112 envelope.
+ *
+ * A declared sharing rule (a stack's `sharingRules`) is read-only and clonable:
+ * it is customised by a clone under ANOTHER name plus the declared rule
+ * switched off in the activation ledger. So no organization-authored row may
+ * take a declared rule's name — not a new row, and not an existing row renamed
+ * onto it. `content/docs/permissions/sharing-rules.mdx` publishes the answer:
+ * `409 RESOURCE_CONFLICT`, for Setup's New and edit forms and for scripts and
+ * imports through the data API.
+ *
+ * The refusal is plugin-sharing's `bindDeclaredRuleNameGuard`
+ * (`DeclaredSharingRuleNameConflictError`), a `beforeInsert` / `beforeUpdate`
+ * hook on `sys_sharing_rule`. Its unit pins drive the hook over a fake engine
+ * and the `POST /sharing/rules` door's pin builds the thrown shape by hand;
+ * neither reaches the door those forms and scripts actually write through.
+ * This file does: a booted composition, an administrator signed in, and
+ * `POST` / `PATCH {basePath}/data/sys_sharing_rule` over the HTTP app, so what
+ * is asserted is the wire answer a client receives — `status` and `code`.
+ * The `/data` door's declared-4xx answer is its flat envelope: `code` is the
+ * machine token at the top level, beside the human `error` sentence
+ * (`mapDataError`, `@objectstack/types`) — read there, not through a fallback
+ * that would also accept the nested `error.code` other families answer.
+ *
+ * Composition: the plugin set, in order, `@objectstack/verify`'s `bootStack`
+ * uses (it mirrors `objectstack dev` / `serve`), as the #21516 and #21454 pins
+ * assemble it, with the production `autoDefaultOrganization` default so the
+ * administrator's rows have an organization to belong to. The declared rules
+ * come from the application's own `sharingRules`, as a real stack declares
+ * them. The boot is paid in `beforeAll`, never inside a case.
+ *
+ * The CONTROL is the same create under a name no declaration holds: it lands,
+ * so the 409 is the guard's answer about the name and not the rig refusing
+ * every write to this object.
+ *
+ * Each refusal targets its OWN declared rule, and `code` is asserted beside
+ * `status`, because this object's unique constraint on the name also answers
+ * 409 (`UNIQUE_VIOLATION`): with one shared name, a create that wrongly landed
+ * would turn the rename's answer into that other 409, and a status-only pin
+ * would read it as the guard's.
+ */
+
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { ObjectKernel } from '@objectstack/core';
+import { ObjectQLPlugin } from '@objectstack/objectql';
+import { HonoServerPlugin } from '@objectstack/plugin-hono-server';
+import { createRestApiPlugin } from '@objectstack/rest';
+import { AuthPlugin } from '@objectstack/plugin-auth';
+import { SecurityPlugin, appSecurityPluginOptions } from '@objectstack/plugin-security';
+import { SharingServicePlugin } from '@objectstack/plugin-sharing';
+import { PlatformObjectsPlugin } from '@objectstack/platform-objects/plugin';
+import { HttpStatusErrorCodeMap } from '@objectstack/spec/api';
+import { AppPlugin } from './app-plugin.js';
+import { DefaultDatasourcePlugin } from './default-datasource-plugin.js';
+import { createDispatcherPlugin } from './dispatcher-plugin.js';
+
+const BOOT_TIMEOUT = 180_000;
+const ORIGIN = 'http://localhost:3000';
+const API = '/api/v1';
+const ADMIN = { email: 'admin@objectos.ai', password: 'admin123' };
+const RULES = '/data/sys_sharing_rule';
+
+/** The declared rule the create targets — a name no authored row may take. */
+const DECLARED_CREATE = 'pin_red_projects_declared';
+/** The declared rule the rename targets. */
+const DECLARED_RENAME = 'pin_amber_projects_declared';
+/** A name no declaration holds: the control's, and the row the rename starts from. */
+const OWN = 'pin_red_projects_ours';
+
+const declaredRule = (name: string, status: string) => ({
+  type: 'criteria',
+  name,
+  label: `${status} projects (declared)`,
+  object: 'pin_project',
+  condition: `record.status == '${status}'`,
+  accessLevel: 'read',
+  sharedWith: { type: 'user', value: 'usr_declared_recipient' },
+  active: true,
+});
+
+const PIN_APP: any = {
+  manifest: { id: 'com.pin.declaredrulename', name: 'Declared rule name pins', version: '1.0.0' },
+  objects: [
+    {
+      name: 'pin_project',
+      label: 'Pin project',
+      fields: {
+        title: { type: 'text', label: 'Title' },
+        status: { type: 'text', label: 'Status' },
+      },
+    },
+  ],
+  sharingRules: [declaredRule(DECLARED_CREATE, 'red'), declaredRule(DECLARED_RENAME, 'amber')],
+};
+
+/** A complete authored row, as Setup's New form posts it. */
+const authoredRow = (name: string) => ({
+  name,
+  label: 'Red projects (ours)',
+  object_name: 'pin_project',
+  criteria_json: JSON.stringify({ status: 'red' }),
+  recipient_type: 'user',
+  recipient_id: 'usr_own_recipient',
+  access_level: 'read',
+});
+
+let kernel: any;
+let httpServer: any;
+let app: any;
+let engine: any;
+let adminToken: string;
+let prevNodeEnv: string | undefined;
+
+const req = (path: string, init?: RequestInit) => app.request(`${ORIGIN}${API}${path}`, init);
+const as = (token: string, method: string, path: string, payload?: unknown) =>
+  req(path, {
+    method,
+    headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${token}` },
+    ...(payload !== undefined ? { body: JSON.stringify(payload) } : {}),
+  });
+
+async function readJson(res: Response): Promise<any> {
+  const text = await res.text();
+  try {
+    return JSON.parse(text);
+  } catch {
+    return text;
+  }
+}
+
+/** The authored rows under `name`, read past every door. */
+const rowsNamed = async (name: string): Promise<any[]> =>
+  engine.find('sys_sharing_rule', { where: { name }, context: { isSystem: true } });
+
+async function signIn(who: { email: string; password: string }): Promise<string> {
+  const res = await req('/auth/sign-in/email', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(who),
+  });
+  if (!res.ok) throw new Error(`pin signIn failed: ${res.status} ${await res.text()}`);
+  return ((await res.json()) as any).token;
+}
+
+beforeAll(async () => {
+  prevNodeEnv = process.env.NODE_ENV;
+  process.env.NODE_ENV = 'development'; // the dev-admin seed, as `objectstack dev` / bootStack arm it
+
+  kernel = new ObjectKernel();
+  await kernel.use(new ObjectQLPlugin());
+  await kernel.use(new DefaultDatasourcePlugin({ driver: 'sqlite-wasm', config: { filename: ':memory:' } }));
+  await kernel.use(new HonoServerPlugin({ port: 0 }));
+  await kernel.use(new AppPlugin(PIN_APP));
+  await kernel.use(new PlatformObjectsPlugin());
+  await kernel.use(new AuthPlugin({ secret: 'declared-rule-name-data-door-secret' }));
+  await kernel.use(new SecurityPlugin(appSecurityPluginOptions(PIN_APP)));
+  await kernel.use(new SharingServicePlugin());
+  await kernel.use(createRestApiPlugin({}));
+  await kernel.use(createDispatcherPlugin({}));
+  await kernel.bootstrap();
+
+  httpServer = await kernel.getServiceAsync('http-server');
+  app = httpServer.getRawApp();
+  engine = await kernel.getServiceAsync('objectql');
+  adminToken = await signIn(ADMIN);
+}, BOOT_TIMEOUT);
+
+afterAll(async () => {
+  try { await httpServer?.close?.(); } catch { /* best-effort */ }
+  try { await kernel?.shutdown?.(); } catch { /* best-effort */ }
+  if (prevNodeEnv === undefined) delete process.env.NODE_ENV;
+  else process.env.NODE_ENV = prevNodeEnv;
+}, 60_000);
+
+describe('[ADR-0131 D6 regime C] precondition and control', () => {
+  it('the application\'s rules are declared, as the sharing-rule service the guard asks reads them', async () => {
+    const rules: any = await kernel.getServiceAsync('sharingRules');
+    for (const name of [DECLARED_CREATE, DECLARED_RENAME]) {
+      expect((await rules.declaredRuleNamed(name))?.name).toBe(name);
+      // A declared rule has no row: nothing below can collide with one.
+      expect(await rowsNamed(name)).toEqual([]);
+    }
+    expect(await rules.declaredRuleNamed(OWN)).toBeNull();
+  });
+
+  it('CONTROL: a create under a name no declaration holds lands through the same door', async () => {
+    const res = await as(adminToken, 'POST', RULES, authoredRow(OWN));
+    const payload = await readJson(res);
+    expect(res.status, JSON.stringify(payload)).toBeGreaterThanOrEqual(200);
+    expect(res.status, JSON.stringify(payload)).toBeLessThan(300);
+    expect(await rowsNamed(OWN)).toHaveLength(1);
+  });
+});
+
+describe('[ADR-0131 D6 regime C] POST / PATCH /data/sys_sharing_rule onto a declared rule\'s name', () => {
+  it('a create taking the declared name answers 409 RESOURCE_CONFLICT, and no row lands', async () => {
+    const res = await as(adminToken, 'POST', RULES, authoredRow(DECLARED_CREATE));
+    const payload = await readJson(res);
+    expect(res.status, JSON.stringify(payload)).toBe(409);
+    expect(payload?.code, JSON.stringify(payload)).toBe('RESOURCE_CONFLICT');
+    // The catalogue's own code for the status, not a restated pair.
+    expect(HttpStatusErrorCodeMap[409]).toBe(payload?.code);
+    expect(await rowsNamed(DECLARED_CREATE)).toEqual([]);
+  });
+
+  it('a rename onto the declared name answers 409 RESOURCE_CONFLICT, and the row keeps its name', async () => {
+    const [own] = await rowsNamed(OWN);
+    expect(own?.id, 'the control row the rename starts from').toBeTruthy();
+
+    const res = await as(adminToken, 'PATCH', `${RULES}/${own.id}`, { name: DECLARED_RENAME });
+    const payload = await readJson(res);
+    expect(res.status, JSON.stringify(payload)).toBe(409);
+    expect(payload?.code, JSON.stringify(payload)).toBe('RESOURCE_CONFLICT');
+    expect(HttpStatusErrorCodeMap[409]).toBe(payload?.code);
+    expect(await rowsNamed(DECLARED_RENAME)).toEqual([]);
+    expect((await rowsNamed(OWN)).map((r) => r.id)).toEqual([own.id]);
+  });
+});