@@ -0,0 +1,24 @@
+---
+'@objectstack/platform-objects': patch
+'@objectstack/runtime': patch
+'@objectstack/mcp': patch
+---
+
+fix(platform-objects)!: the platform-admin actions declare their gate, so MCP `list_actions` no longer lists them to a caller who cannot run them, and both action doors refuse that caller themselves
+
+Clause-②: yes (narrowing)
+Metadata-protocol: none
+
+<!-- adr-0087: not-required (no-migration-prescription) nothing an author wrote is retired or renamed: the change adds `requiredPermissions` to fifteen first-party action declarations, so stored metadata needs no rewrite, and the one thing an upgrader may act on (a legacy role-only admin needing the admin_full_access set or OS_PLATFORM_OWNER_EMAIL) is a grant, not a metadata edit -->
+
+**BREAKING.** The 15 first-party actions whose door runs the platform-admin gate (on `sys_user`: `ban_user`, `unban_user`, `unlock_user`, `create_user`, `set_user_password`, `impersonate_user`, `set_user_manager`, `list_platform_admins`; on `sys_member`: `add_member`; on `sys_oauth_application`: `disable_oauth_application`, `enable_oauth_application`; on `sys_sso_provider`: `register_sso_provider`, `register_saml_provider`, `request_domain_verification`, `verify_domain`) now declare `requiredPermissions`: `['manage_users']` for the account and membership doors, `['manage_platform_settings']` for the OAuth application and SSO doors. It is the existing ADR-0066 D4 key, read by one runtime check for MCP `list_actions`, MCP `run_action` and `POST /api/v1/actions/:object/:action`. A platform administrator holds both capabilities on either way of becoming one (the `admin_full_access` grant or `OS_PLATFORM_OWNER_EMAIL`), so nothing changes for them.
+
+What changes, before and now:
+
+- **MCP `list_actions`.** Before: every caller was listed all of these actions (a plain member saw `ban_user` and `set_user_manager`). Now: a caller without the capability is not listed them.
+- **The refusal at `POST /actions/:object/:action` and MCP `run_action`.** Before: the door forwarded the call and the target answered 403 `PERMISSION_DENIED` "Admin role required". Now: nothing reaches the target. `POST /actions/...` answers 403 itself, with the capability sentence (`Action 'ban_user' on 'sys_user' requires capability [manage_users] — caller is missing [manage_users]`), and MCP `run_action` answers the same sentence as `PERMISSION_DENIED` with status 403, whether it is called by `actionName` alone or with `objectName`.
+- **A caller whose only admin standing is the legacy better-auth `role === 'admin'` scalar** (no `admin_full_access` grant, not in `OS_PLATFORM_OWNER_EMAIL`). Before: the action doors forwarded the call and the target admitted it. Now: the action doors refuse it 403, because that caller holds no `manage_users` / `manage_platform_settings`. The target endpoints themselves (`/api/v1/auth/admin/*`) are unchanged and still admit it; give the account the `admin_full_access` permission set, or list its email in `OS_PLATFORM_OWNER_EMAIL`, to keep it on the action doors.
+
+**MCP `run_action` refusal codes (`@objectstack/runtime`, `@objectstack/mcp`).** The capability gate's refusal at MCP `run_action` used to be a plain message; it now carries `code: 'PERMISSION_DENIED'` and `status: 403`, the REST door's answer, for every action with `requiredPermissions`. With `objectName` on a `sys_*` object, the MCP tools admit an action only where `list_actions` lists it, and answered every action missing from the listing with the system-object sentence (`… is not exposed via MCP …`). An action that IS exposed but whose gate refuses the caller now gets the gate's refusal there too, through a new optional `McpActionBridge.capabilityRefusal(name, objectName)` the runtime bridge implements; an action not exposed to AI keeps the system-object sentence, and a bridge without the member behaves as before.
+
+What does not change: the target endpoints judge the platform-admin standing as before, the console shows and hides these buttons from their `visible` standing as before, and an action on another object is unaffected.
@@ -131,3 +131,46 @@ describe('[#27681] run_action: a sys_* action runs only where list_actions lists
     expect(bridge.runs).toEqual(['complete_task']);
   });
 });
+
+describe('[#30771] run_action: a sys_* action left out for the caller\'s capability answers the gate, not the system-object sentence', () => {
+  const GATE = "Action 'ban_user' on 'sys_user' requires capability [manage_users] — caller is missing [manage_users]";
+  /** The bridge's answer for an exposed action whose declared gate refuses this caller. */
+  const withCapabilityRefusal = (listing: McpActionSummary[]) => {
+    const bridge = makeBridge(listing);
+    const asked: Array<[string, string]> = [];
+    return Object.assign(bridge, {
+      asked,
+      async capabilityRefusal(name: string, objectName: string) {
+        asked.push([name, objectName]);
+        return name === 'ban_user' ? { code: 'PERMISSION_DENIED', status: 403, message: GATE } : undefined;
+      },
+    });
+  };
+
+  it('answers the bridge\'s capability refusal (403, PERMISSION_DENIED, the gate\'s sentence) and runs nothing', async () => {
+    const bridge = withCapabilityRefusal([APP]);
+    const json = await call(bridge, toolsCall(7, 'run_action', { actionName: 'ban_user', objectName: SYS, recordId: 'u1' }));
+    expect(json.result.isError).toBe(true);
+    const body = JSON.parse(json.result.content[0].text);
+    expect(body.error).toMatchObject({ code: 'PERMISSION_DENIED', status: 403, message: GATE });
+    expect(String(json.result.content[0].text)).not.toMatch(/is not exposed via MCP/);
+    expect(bridge.asked).toEqual([['ban_user', SYS]]);
+    expect(bridge.runs).toEqual([]);
+  });
+
+  it('CONTROL — an action the bridge answers no capability refusal for keeps the system-object sentence', async () => {
+    const bridge = withCapabilityRefusal([APP]);
+    const json = await call(bridge, toolsCall(8, 'run_action', { actionName: 'unban_user', objectName: SYS, recordId: 'u1' }));
+    expect(json.result.isError).toBe(true);
+    expect(String(json.result.content[0].text)).toMatch(/system object "sys_user" is not exposed via MCP/);
+    expect(bridge.runs).toEqual([]);
+  });
+
+  it('CONTROL — a listed action never asks: the listing admits it as before', async () => {
+    const bridge = withCapabilityRefusal([EXPOSED]);
+    const json = await call(bridge, toolsCall(9, 'run_action', { actionName: 'ban_user', objectName: SYS, recordId: 'u1' }));
+    expect(json.result.isError, JSON.stringify(json.result)).toBeFalsy();
+    expect(bridge.asked).toEqual([]);
+    expect(bridge.runs).toEqual(['ban_user']);
+  });
+});
@@ -315,6 +315,18 @@ export interface McpActionBridge {
     name: string,
     input: { objectName?: string; recordId?: string; params?: Record<string, unknown> } & AIActionConfirmation,
   ): Promise<unknown>;
+  /**
+   * [#30771] The capability refusal `runAction` would throw for an action on
+   * `objectName` that {@link listActions} leaves out because the caller lacks
+   * its declared `requiredPermissions` — `{ code, status, message }`, the same
+   * values the by-name call throws. `undefined` for anything else (not
+   * declared, not exposed to AI), so `run_action`'s scoped `sys_*` pre-screen
+   * keeps its system-object refusal there. Runs nothing.
+   *
+   * OPTIONAL: a bridge without it keeps the system-object refusal for every
+   * `sys_*` action its listing leaves out, as before.
+   */
+  capabilityRefusal?(name: string, objectName: string): Promise<ThrownRefusalEnvelope | undefined>;
   /**
    * [#15705] Continue a run that `runAction` answered with `status: 'paused'`
    * and a `screen`, submitting that screen's field values as `values`.
@@ -1783,7 +1795,15 @@ export function registerActionTools(
           const admitted = listed.some(
             (a) => a.name === actionName && a.objectName === objectName && isListableAction(a),
           );
-          if (!admitted) return errorResult(systemObjectActionRefusal(actionName, objectName));
+          if (!admitted) {
+            // [#30771] An exposed action the caller's declared gate refuses is
+            // left out of the listing too: answer that gate's refusal, the one
+            // the by-name call gets, not the system-object sentence. Nothing
+            // runs either way.
+            const refusal = await bridge.capabilityRefusal?.(actionName, objectName);
+            if (refusal) return errorResultWithCode(Object.assign(new Error(refusal.message), refusal));
+            return errorResult(systemObjectActionRefusal(actionName, objectName));
+          }
         }
         const result = await bridge.runAction(actionName, {
           objectName,
 
@@ -0,0 +1,40 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * The declared gate of a first-party action whose door runs the ADR-0068
+ * platform-admin gate (#30771, ruling A on #30126 row 16).
+ *
+ * ## Why the action declares it
+ *
+ * Such a door answers every caller below the ADR-0095 D3 `PLATFORM_ADMIN` rung
+ * 403. Its action used to carry that fact only in `visible`, which is display
+ * only: no door reads it. So MCP `list_actions` listed `ban_user` and
+ * `set_user_manager` to a plain member, and the platform action door
+ * (`POST /actions/:object/:action`, MCP `run_action`) forwarded the call for the
+ * target to refuse. Declaring the gate in `requiredPermissions` (ADR-0066 D4,
+ * an existing key) puts it where both doors already look: the runtime's ONE
+ * reader, `actionPermissionError`, refuses the call with 403 at the door and
+ * leaves the action out of `list_actions`, from this one declaration.
+ *
+ * ## Why a capability stands for the rung
+ *
+ * The rung is not a key an action can name, but the rung implies these
+ * capabilities by construction: both anchors that confer it (the stored
+ * `admin_full_access` grant and the deployment's `OS_PLATFORM_OWNER_EMAIL`
+ * list) hand the holder `ADMIN_FULL_ACCESS_CAPABILITIES.systemPermissions`,
+ * and both names below are catalog `scope: 'platform'` capabilities that
+ * `organization_admin` withholds. So the declaration never hides the action from
+ * a caller its door admits on the rung, and the door still judges the rung
+ * itself: a holder of the capability without the rung is listed and refused by
+ * the target, as before.
+ *
+ * Pinned, for every action on such a door, by
+ * `platform-admin-affordance-standing.test.ts` (both halves: the `visible`
+ * standing and this declaration).
+ */
+
+/** Doors that administer accounts and memberships across the platform. */
+export const PLATFORM_ADMIN_USERS_GATE: readonly string[] = Object.freeze(['manage_users']);
+
+/** Doors that administer platform-wide settings: OAuth applications, SSO providers. */
+export const PLATFORM_ADMIN_SETTINGS_GATE: readonly string[] = Object.freeze(['manage_platform_settings']);
@@ -1,6 +1,7 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { ObjectSchema, Field } from '@objectstack/spec/data';
+import { PLATFORM_ADMIN_USERS_GATE } from './platform-admin-action-gate.js';
 import { F } from '@objectstack/spec/shared';
 import {
   BUILTIN_MEMBERSHIP_ROLE_OPTIONS,
@@ -177,6 +178,8 @@ export const SysMember = ObjectSchema.create({
       locations: ['list_toolbar'],
       type: 'api',
       target: '/api/v1/auth/organization/add-member',
+      // The door's platform-admin gate, declared where both action doors read it (#30771).
+      requiredPermissions: [...PLATFORM_ADMIN_USERS_GATE],
       // Offered only to the one standing the door admits (ADR-0068 D4):
       // `current_user.isPlatformAdmin` is the ADR-0095 D3 PLATFORM_ADMIN
       // posture rung — what the session payload emits and what the mount's
 
@@ -1,6 +1,7 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { ObjectSchema, Field } from '@objectstack/spec/data';
+import { PLATFORM_ADMIN_SETTINGS_GATE } from './platform-admin-action-gate.js';
 
 /**
  * sys_oauth_application — Registered OAuth/OIDC client application
@@ -98,6 +99,8 @@ export const SysOauthApplication = ObjectSchema.create({
       type: 'api',
       method: 'POST',
       target: '/api/v1/auth/admin/oauth2/toggle-disabled',
+      // The door's platform-admin gate, declared where both action doors read it (#30771).
+      requiredPermissions: [...PLATFORM_ADMIN_SETTINGS_GATE],
       requiresFeature: 'oidcProvider',
       // The confirm question rides `description`, not `confirmText`: this action
       // collects params, and the console action runner chains confirmation THEN
@@ -131,6 +134,8 @@ export const SysOauthApplication = ObjectSchema.create({
       type: 'api',
       method: 'POST',
       target: '/api/v1/auth/admin/oauth2/toggle-disabled',
+      // The door's platform-admin gate, declared where both action doors read it (#30771).
+      requiredPermissions: [...PLATFORM_ADMIN_SETTINGS_GATE],
       requiresFeature: 'oidcProvider',
       // Confirm question on `description` — one dialog, not two (#7278/#7309).
       description: 'Re-enable this OAuth application? Token issuance, authorization, and introspection will resume immediately.',
 
@@ -1,6 +1,7 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { ObjectSchema, Field } from '@objectstack/spec/data';
+import { PLATFORM_ADMIN_SETTINGS_GATE } from './platform-admin-action-gate.js';
 
 /**
  * sys_sso_provider — Registered external SSO identity provider (OIDC / SAML)
@@ -101,6 +102,8 @@ export const SysSsoProvider = ObjectSchema.create({
       // /sso/register would drop clientId/clientSecret (top-level → Zod-stripped)
       // and persist an unusable `oidc_config = null` provider.
       target: '/api/v1/auth/admin/sso/register',
+      // The door's platform-admin gate, declared where both action doors read it (#30771).
+      requiredPermissions: [...PLATFORM_ADMIN_SETTINGS_GATE],
       // Platform-admin standing (ADR-0068 D4) — see the actions header above.
       visible: 'current_user.isPlatformAdmin == true',
       refreshAfter: true,
@@ -143,6 +146,8 @@ export const SysSsoProvider = ObjectSchema.create({
       // re-dispatches to /sso/register (admin gate runs). The response returns
       // the SP ACS + metadata URLs to configure on the IdP.
       target: '/api/v1/auth/admin/sso/register-saml',
+      // The door's platform-admin gate, declared where both action doors read it (#30771).
+      requiredPermissions: [...PLATFORM_ADMIN_SETTINGS_GATE],
       // Platform-admin standing (ADR-0068 D4) — see the actions header above.
       visible: 'current_user.isPlatformAdmin == true',
       refreshAfter: true,
@@ -175,6 +180,8 @@ export const SysSsoProvider = ObjectSchema.create({
       // feature is OFF the bridge returns a clear "not enabled for this
       // environment" error instead of a bare 404.
       target: '/api/v1/auth/admin/sso/request-domain-verification',
+      // The door's platform-admin gate, declared where both action doors read it (#30771).
+      requiredPermissions: [...PLATFORM_ADMIN_SETTINGS_GATE],
       // Platform-admin standing (ADR-0068 D4) — see the actions header above.
       visible: 'current_user.isPlatformAdmin == true',
       params: [
@@ -211,6 +218,8 @@ export const SysSsoProvider = ObjectSchema.create({
       // on success. Routed through the env bridge, which maps @better-auth/sso's
       // empty 204 / 502 into a clear success/error toast.
       target: '/api/v1/auth/admin/sso/verify-domain',
+      // The door's platform-admin gate, declared where both action doors read it (#30771).
+      requiredPermissions: [...PLATFORM_ADMIN_SETTINGS_GATE],
       // Platform-admin standing (ADR-0068 D4) — see the actions header above.
       visible: 'current_user.isPlatformAdmin == true',
       successMessage: 'Domain ownership verified',