diff --git a/.changeset/23529-mcp-action-tools-withhold-permission-details.md b/.changeset/23529-mcp-action-tools-withhold-permission-details.md
new file mode 100644
index 00000000000..5d70bc19ee9
--- /dev/null
+++ b/.changeset/23529-mcp-action-tools-withhold-permission-details.md
@@ -0,0 +1,11 @@
+---
+'@objectstack/mcp': patch
+---
+
+fix(mcp): `run_action` and `resume_run` withhold a `PERMISSION_DENIED` refusal's `details`, as the data tools already do (#23529)
+
+**What was wrong.** The two action tools render a thrown coded refusal through `errorResultFromThrown`, which served the refusal's `details` verbatim. The security gate's `PERMISSION_DENIED` carries the caller's own positions and permission-set names in `details`. Those are server-side diagnostics. The runtime dispatcher and the REST actions door withhold them, and the data tools and the record resource never serve a refusal's `details`. The action tools were the one place on the MCP surface that still served them, and `executeDeclarativeUpdateAction` writes as the caller, so the gate's write-side refusal reaches that renderer.
+
+**What a client reads now.** A `PERMISSION_DENIED` on `run_action` or `resume_run` answers the shape the data tools answer: `isError: true`, and the text is the JSON `{ "error": { "code", "message", "status" } }` with no `details`. The code, the message and the status are unchanged.
+
+Every other coded refusal on the two tools is unchanged. `ACTION_CONFIRMATION_REQUIRED` keeps the `details` that name the action and the member to set, and `resume_run`'s other refusals keep theirs. A throw with no code still answers its bare message.
diff --git a/packages/mcp/src/mcp-action-refusal-details.test.ts b/packages/mcp/src/mcp-action-refusal-details.test.ts
new file mode 100644
index 00000000000..18164a96266
--- /dev/null
+++ b/packages/mcp/src/mcp-action-refusal-details.test.ts
@@ -0,0 +1,186 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#23529] `run_action` and `resume_run` WITHHOLD a permission refusal's
+ * `details`, as the data tools do (#23509) and as the runtime dispatcher does
+ * (the ruling on #7450).
+ *
+ * ## What was open
+ *
+ * The security gate's `PERMISSION_DENIED` carries the caller's `positions` and
+ * `permissionSets` in `details`. Those are server-side diagnostics: the
+ * dispatcher drops them from the wire, the REST actions door answers through
+ * the closed `details` list of `resolveThrownHttpError`, and the data tools
+ * render through `errorResultWithCode`, which never reads `details`. The two
+ * action tools rendered through `errorResultFromThrown`, which spread a thrown
+ * refusal's `details` verbatim into a tool result. The tool result rides a
+ * JSON-RPC 200, so the dispatcher's withholding never saw it.
+ *
+ * The reachable producer, read from source: a declarative update action
+ * (`operation: 'update'`) writes as the caller. A caller who may read the row
+ * but not update the object passes the subject load and meets the gate's
+ * write-side refusal, and nothing between the gate and this package catches
+ * it. A host script handler that rethrows a caller-scope refusal surfaces the
+ * same way.
+ *
+ * ## What is pinned here
+ *
+ *  - The HTTP `/mcp` face, through `handleHttpRequest` and the real Streamable
+ *    HTTP transport, as `mcp-coded-refusal.test.ts` drives it. The bridge is a
+ *    double, because this package does not depend on `@objectstack/runtime`:
+ *    it lets the caller read the subject row and refuses the declarative
+ *    update with the gate's `PermissionDeniedError` shape.
+ *  - The refusal answers `code` `PERMISSION_DENIED` and status 403, and the
+ *    caller's position and permission-set NAMES appear nowhere in the HTTP
+ *    response body: not under `details`, not anywhere else. A key-presence
+ *    check would pass a renderer that moved the names to another key.
+ *  - `resume_run` renders through the same function. No caller-scope write of
+ *    its own reaches it today (it re-reads the subject through the not-found
+ *    door), so its row pins the renderer, not a measured producer.
+ *  - The control: on the same two tools, `ACTION_CONFIRMATION_REQUIRED` still
+ *    serves its `details` (#15942). So the withholding is keyed on the
+ *    refusal's code, and the `details` channel is shown to be live.
+ */
+
+import { describe, it, expect } from 'vitest';
+
+import { AI_ACTION_CONFIRMATION_MEMBER } from '@objectstack/spec/contracts';
+
+import { MCPServerRuntime } from './mcp-server-runtime.js';
+import type { McpActionBridge, McpDataBridge } from './mcp-http-tools.js';
+
+type Bridge = McpDataBridge & McpActionBridge;
+
+const OBJECT = 'crm_case';
+const RECORD_ID = 'case_1';
+/** A declarative update action: `operation: 'update'` writes the patch as the caller. */
+const ACTION = 'close_case';
+const RUN_ID = 'run_1';
+
+/** Distinctive names, so a hit in the response body can only be a disclosure. */
+const POSITIONS = ['pin23529_position_case_reader', 'pin23529_position_everyone'];
+const PERMISSION_SETS = ['pin23529_set_case_read_only', 'pin23529_set_member_default'];
+
+const DENIAL_MESSAGE =
+  'You do not have permission to perform this action. Contact your administrator if you need access.';
+
+/**
+ * The security gate's write-side refusal, in the shape `PermissionDeniedError`
+ * gives it: the localized sentence, `code`, both status spellings, the
+ * diagnostics in `details`, and the operator's sentence as a SIBLING of
+ * `details`.
+ */
+function writeSideDenial(): Error {
+  const err = Object.assign(new Error(DENIAL_MESSAGE), {
+    code: 'PERMISSION_DENIED',
+    status: 403,
+    statusCode: 403,
+    details: { operation: 'update', object: OBJECT, positions: POSITIONS, permissionSets: PERMISSION_SETS },
+    developerMessage:
+      `[Security] Access denied: operation 'update' on object '${OBJECT}' `
+      + `is not permitted for positions [${POSITIONS.join(', ')}]`,
+  });
+  err.name = 'PermissionDeniedError';
+  return err;
+}
+
+/** The runtime's confirmation refusal (#15942): its `details` are the retry contract. */
+function confirmationRefusal(): Error {
+  return Object.assign(
+    new Error(`Action '${ACTION}' on '${OBJECT}' declares ai.requiresConfirmation: true — nothing was run.`),
+    {
+      code: 'ACTION_CONFIRMATION_REQUIRED',
+      status: 428,
+      details: { actionName: ACTION, objectName: OBJECT, confirmationMember: AI_ACTION_CONFIRMATION_MEMBER },
+    },
+  );
+}
+
+/**
+ * A caller who may READ the subject row and may not UPDATE the object. The
+ * subject read answers the row; the declarative update (and the run it would
+ * resume) is refused by the gate with `thrown`.
+ */
+function readerBridge(thrown: () => Error): Bridge {
+  return {
+    async listObjects() { return [{ name: OBJECT, label: 'Case', fieldCount: 1 }]; },
+    async describeObject() { return { name: OBJECT, fields: [{ name: 'status', type: 'text' }] }; },
+    async query() { return { object: OBJECT, records: [], total: 0 }; },
+    async get(_object, id) { return { id, status: 'open' }; },
+    async create() { return {}; },
+    async update() { throw thrown(); },
+    async remove() { return {}; },
+    async listActions() {
+      return [{ name: ACTION, objectName: OBJECT, type: 'script', requiresRecord: true, requiresConfirmation: false }];
+    },
+    async runAction() { throw thrown(); },
+    async resumeRun() { throw thrown(); },
+  };
+}
+
+let nextId = 1;
+
+/** One `tools/call` over the real HTTP transport; answers the raw body text and the parsed tool result. */
+async function callOverHttp(bridge: Bridge, name: string, args: Record<string, unknown>) {
+  const body = { jsonrpc: '2.0', id: nextId++, method: 'tools/call', params: { name, arguments: args } };
+  const runtime = new MCPServerRuntime({ name: 'pin', version: '0.0.0' });
+  const res = await runtime.handleHttpRequest(
+    new Request('http://localhost/api/v1/mcp', {
+      method: 'POST',
+      headers: { 'content-type': 'application/json', accept: 'application/json, text/event-stream' },
+      body: JSON.stringify(body),
+    }),
+    { bridge, parsedBody: body },
+  );
+  expect(res.status, `${name}: the HTTP transport itself answered ${res.status}`).toBe(200);
+  const raw = await res.text();
+  const json = JSON.parse(raw) as { result?: any; error?: unknown };
+  expect(json.error, `${name}: JSON-RPC error ${JSON.stringify(json.error)}`).toBeUndefined();
+  return { raw, result: json.result };
+}
+
+const DOORS = [
+  { tool: 'run_action', args: { actionName: ACTION, objectName: OBJECT, recordId: RECORD_ID } },
+  { tool: 'resume_run', args: { runId: RUN_ID, values: {} } },
+] as const;
+
+describe('run_action / resume_run over HTTP /mcp: a permission refusal withholds its details (#23529)', () => {
+  it('control: the caller may read the subject row', async () => {
+    const { result } = await callOverHttp(readerBridge(writeSideDenial), 'get_record', {
+      objectName: OBJECT,
+      recordId: RECORD_ID,
+    });
+    expect(result.isError).toBeFalsy();
+    expect(JSON.parse(result.content[0].text)).toEqual({ id: RECORD_ID, status: 'open' });
+  });
+
+  for (const door of DOORS) {
+    it(`${door.tool}: PERMISSION_DENIED answers code, message and status, and the caller's grants appear nowhere`, async () => {
+      const { raw, result } = await callOverHttp(readerBridge(writeSideDenial), door.tool, door.args);
+
+      expect(result.isError).toBe(true);
+      expect(result.content).toHaveLength(1);
+      expect(JSON.parse(result.content[0].text)).toEqual({
+        error: { code: 'PERMISSION_DENIED', message: DENIAL_MESSAGE, status: 403 },
+      });
+      // Every name, against the whole HTTP response body, not one key.
+      for (const name of [...POSITIONS, ...PERMISSION_SETS]) {
+        expect(raw, `${door.tool}: '${name}' reached the wire`).not.toContain(name);
+      }
+    });
+
+    it(`${door.tool}: control — ACTION_CONFIRMATION_REQUIRED still serves its retry details (#15942)`, async () => {
+      const { result } = await callOverHttp(readerBridge(confirmationRefusal), door.tool, door.args);
+
+      expect(result.isError).toBe(true);
+      expect(JSON.parse(result.content[0].text)).toEqual({
+        error: {
+          code: 'ACTION_CONFIRMATION_REQUIRED',
+          message: `Action '${ACTION}' on '${OBJECT}' declares ai.requiresConfirmation: true — nothing was run.`,
+          status: 428,
+          details: { actionName: ACTION, objectName: OBJECT, confirmationMember: AI_ACTION_CONFIRMATION_MEMBER },
+        },
+      });
+    });
+  }
+});
diff --git a/packages/mcp/src/mcp-http-tools.ts b/packages/mcp/src/mcp-http-tools.ts
index b7a491d6641..232f1b56c01 100644
--- a/packages/mcp/src/mcp-http-tools.ts
+++ b/packages/mcp/src/mcp-http-tools.ts
@@ -35,6 +35,9 @@
 import { z } from 'zod';
 import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 import type { EngineAggregateOptions } from '@objectstack/spec/data';
+// [#23529] The catalogue's spelling of `PERMISSION_DENIED`, the code whose
+// `details` `errorResultFromThrown` withholds. Imported, never hand-spelled.
+import { StandardErrorCode } from '@objectstack/spec/api';
 import {
   MCP_OAUTH_SCOPE_DATA_READ,
   MCP_OAUTH_SCOPE_DATA_WRITE,
@@ -302,16 +305,35 @@ function errorResult(message: string) {
  * nobody and the agent is back to guessing the member's spelling from
  * documentation.
  *
- * Uncoded throws fall through to `errorResult` unchanged, so this widens what a
- * caller can read and narrows nothing.
+ * Uncoded throws fall through to `errorResult` unchanged.
  *
  * `run_action` and `resume_run` only. The other catches render through
  * {@link errorResultWithCode}, which serves the same envelope WITHOUT `details`;
  * that function says why.
+ *
+ * [#23529] ⛔ A `PERMISSION_DENIED` is the exception: it renders through
+ * {@link errorResultWithCode}, so its `details` are WITHHELD here too. The
+ * security gate puts the caller's `positions` and `permissionSets` in those
+ * `details`; the ruling on #7450 keeps them off the wire, and the runtime
+ * dispatcher and the REST actions door both drop them. These two tools are
+ * reachable by that refusal: a declarative update action writes as the caller,
+ * so a caller who may read the row but not update it meets the gate's
+ * write-side refusal, and a host script handler can rethrow one. The answer is
+ * a tool result inside a JSON-RPC 200, which the dispatcher's withholding never
+ * sees, so it is withheld at this renderer.
+ *
+ * The question is asked on the DECLARED code, spelled from the spec's standard
+ * catalogue rather than restated, and answered with the data tools' own
+ * function rather than a second filter of `details`. Every `PermissionDeniedError`
+ * declares this code (it is a class constant), and a throw with no code never
+ * reaches the `details` read at all. Every other coded refusal keeps its
+ * `details` as before, so #15942's confirmation contract and `resume_run`'s
+ * REST-built `details` are unchanged.
  */
 function errorResultFromThrown(err: unknown) {
   const envelope = thrownRefusalEnvelope(err);
   if (!envelope) return errorResult(messageOf(err));
+  if (envelope.code === StandardErrorCode.enum.PERMISSION_DENIED) return errorResultWithCode(err);
   const details = (err as { details?: unknown }).details;
   return codedErrorResult({ ...envelope, ...(details !== undefined ? { details } : {}) });
 }