diff --git a/.changeset/23532-hono-undeclared-500-leak-filter.md b/.changeset/23532-hono-undeclared-500-leak-filter.md
new file mode 100644
index 00000000000..cd2bdcd6f64
--- /dev/null
+++ b/.changeset/23532-hono-undeclared-500-leak-filter.md
@@ -0,0 +1,17 @@
+---
+'@objectstack/hono': patch
+---
+
+fix(hono): `createHonoApp`'s catch arms withhold a driver diagnostic from an undeclared `500` instead of shipping it to the client (#23532)
+
+Clause-②: no
+
+`@objectstack/hono`'s `createHonoApp` has two catch arms: the auth mount's, and the `${prefix}/*` catch-all's around `HttpDispatcher.dispatch()`. A throw that does not declare an ADR-0112 envelope is answered from its own `message`, and that message was shipped unread. A driver diagnostic therefore reached the client verbatim: on a host whose object `ghost` was registered but whose table was never synced, `POST /api/v1/data/ghost` answered `500 INTERNAL_ERROR` with the message `insert into [statement and bound values redacted] - no such table: ghost`, naming the SQLite error and the physical table.
+
+**What changed.** Before it ships that message, the arm now asks `looksLikeInternalErrorLeak` (`@objectstack/types`), as every other door that emits a thrown message already does: `HttpDispatcher.error`, the REST registrars, `@objectstack/plugin-hono-server`'s direct-mount routes and this adapter's own `/auth/config` arm. When the answer is a `5xx` and the message looks like a driver or SQL dump, the message is replaced by the same text those doors use, `Internal server error`. The status and the `code` are unchanged.
+
+**What did NOT change:**
+
+- a `5xx` whose message does not look like a dump keeps it: a bare `new Error('boom')` is still `500 INTERNAL_ERROR` with the message `boom`;
+- a `4xx` keeps its message, as on the other doors, because a `4xx` message is an answer meant for the caller;
+- a throw that declares an ADR-0112 envelope is answered as declared, as before.
diff --git a/packages/adapters/hono/src/hono-thrown-message-disclosure.test.ts b/packages/adapters/hono/src/hono-thrown-message-disclosure.test.ts
new file mode 100644
index 00000000000..fce0c51db78
--- /dev/null
+++ b/packages/adapters/hono/src/hono-thrown-message-disclosure.test.ts
@@ -0,0 +1,154 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#23532] `createHonoApp`'s two catch arms run the 5xx disclosure filter
+ * before they ship an UNDECLARED throw's message.
+ *
+ * ## The defect
+ *
+ * Both arms (the `${authMount}/*` mount's and the `${prefix}/*` catch-all's
+ * around `HttpDispatcher.dispatch()`) end in `thrownJson`. A throw the ADR-0112
+ * recogniser does not accept fell to `errorJson(c, err.message, …)` with the
+ * message unread, so a driver diagnostic reached the client verbatim. Measured
+ * through a real host (an object registered, its table never synced):
+ *
+ *     POST /api/v1/data/ghost
+ *       500 {"success":false,"error":{"code":"INTERNAL_ERROR",
+ *            "message":"insert into [statement and bound values redacted] - no such table: ghost"}}
+ *
+ * The driver had already redacted the statement and its values; the SQLite
+ * diagnostic and the physical table name still went out. Every other door that
+ * emits a thrown message asks `looksLikeInternalErrorLeak` first
+ * (`HttpDispatcher.error`, `packages/rest`'s registrars, the recogniser's own
+ * 5xx limb, and this file's `/auth/config` arm), so this one now does too.
+ *
+ * ## What is pinned, per arm
+ *
+ *  - the probe above, as the throw: `500`, `INTERNAL_ERROR`, and the twins'
+ *    `INTERNAL_ERROR_MESSAGE` in place of the message; neither the table name
+ *    nor the diagnostic is anywhere in the body;
+ *  - a plain `new Error('boom')`: `500`, `INTERNAL_ERROR`, `boom` — an ordinary
+ *    undeclared 5xx still names itself.
+ *
+ * And the filter's scope on the catch-all, the same as the twins': a 5xx that
+ * declares its status through `statusCode` is filtered at that status, and a
+ * 4xx keeps its message, because a 4xx message is a caller-facing answer.
+ *
+ * ## What this file is
+ *
+ * This package's vitest config aliases `@objectstack/runtime` to a stub, so the
+ * dispatcher here is a fixture whose methods throw what a case hands them;
+ * `createHonoApp`, both of its arms and `thrownJson` are the real source.
+ * The composed-host sibling, a real kernel and the real dispatcher, is
+ * `packages/qa/http-conformance/src/hono-declared-envelope.conformance.test.ts`.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { INTERNAL_ERROR_MESSAGE } from '@objectstack/types';
+
+const mockDispatcher = {
+  getDiscoveryInfo: vi.fn().mockReturnValue({ version: '1.0', routes: {} }),
+  handleAuth: vi.fn(),
+  dispatch: vi.fn(),
+};
+
+vi.mock('@objectstack/runtime', () => ({
+  HttpDispatcher: function HttpDispatcher() { return mockDispatcher; },
+}));
+
+import { createHonoApp } from './index';
+
+const PREFIX = '/api/v1';
+/** The card's probe: the message the SQL driver threw for an unsynced table. */
+const PROBE = 'insert into [statement and bound values redacted] - no such table: ghost';
+const PLAIN = 'boom';
+
+interface Answer { status: number; body: any; text: string }
+
+const send = async (app: ReturnType<typeof createHonoApp>, method: string, path: string): Promise<Answer> => {
+  const res = await app.request(`http://localhost${path}`, {
+    method,
+    ...(method === 'GET' ? {} : { headers: { 'content-type': 'application/json' }, body: JSON.stringify({ name: 'x' }) }),
+  });
+  const text = await res.text();
+  return { status: res.status, body: JSON.parse(text), text };
+};
+
+/** A kernel whose `auth` service's `handleRequest` throws `thrown`. */
+const kernelWithThrowingAuth = (thrown: unknown) => ({
+  name: 'test-kernel',
+  getServiceAsync: vi.fn(async () => ({ handleRequest: vi.fn(async () => { throw thrown; }) })),
+});
+
+const withheld = { success: false, error: { code: 'INTERNAL_ERROR', message: INTERNAL_ERROR_MESSAGE } };
+const kept = (message: string) => ({ success: false, error: { code: 'INTERNAL_ERROR', message } });
+
+/** The disclosure itself, independent of the replacement text. */
+const expectNoDiagnostic = (a: Answer) => {
+  expect(a.text).not.toContain('ghost');
+  expect(a.text).not.toContain('no such table');
+};
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe('[#23532] the dispatch() catch-all arm', () => {
+  const app = () => createHonoApp({ kernel: { name: 'test-kernel' } as any, prefix: PREFIX, cors: false });
+
+  it('a driver diagnostic thrown undeclared: 500 INTERNAL_ERROR with the withheld message', async () => {
+    mockDispatcher.dispatch.mockRejectedValueOnce(new Error(PROBE));
+    const answer = await send(app(), 'POST', `${PREFIX}/data/ghost`);
+    expect(answer.status, answer.text).toBe(500);
+    expect(answer.body).toEqual(withheld);
+    expectNoDiagnostic(answer);
+  });
+
+  it('control: a plain bare Error keeps its message', async () => {
+    mockDispatcher.dispatch.mockRejectedValueOnce(new Error(PLAIN));
+    const answer = await send(app(), 'POST', `${PREFIX}/data/ghost`);
+    expect(answer.status, answer.text).toBe(500);
+    expect(answer.body).toEqual(kept(PLAIN));
+  });
+
+  it('a 5xx declared through `statusCode` alone is filtered at that status', async () => {
+    mockDispatcher.dispatch.mockRejectedValueOnce(Object.assign(new Error(PROBE), { statusCode: 503 }));
+    const answer = await send(app(), 'GET', `${PREFIX}/data/ghost`);
+    expect(answer.status, answer.text).toBe(503);
+    expect(answer.body).toEqual({ success: false, error: { code: 'SERVICE_UNAVAILABLE', message: INTERNAL_ERROR_MESSAGE } });
+    expectNoDiagnostic(answer);
+  });
+
+  it('scope: a 4xx keeps its message, as on the twin doors', async () => {
+    mockDispatcher.dispatch.mockRejectedValueOnce(Object.assign(new Error(PROBE), { statusCode: 400 }));
+    const answer = await send(app(), 'GET', `${PREFIX}/data/ghost`);
+    expect(answer.status, answer.text).toBe(400);
+    expect(answer.body.error.message).toBe(PROBE);
+  });
+});
+
+describe('[#23532] the auth-mount arm', () => {
+  it('an auth service that throws a driver diagnostic: 500 INTERNAL_ERROR with the withheld message', async () => {
+    const app = createHonoApp({ kernel: kernelWithThrowingAuth(new Error(PROBE)) as any, prefix: PREFIX, cors: false });
+    const answer = await send(app, 'GET', `${PREFIX}/auth/get-session`);
+    expect(answer.status, answer.text).toBe(500);
+    expect(answer.body).toEqual(withheld);
+    expectNoDiagnostic(answer);
+  });
+
+  it('control: an auth service that throws a plain bare Error keeps its message', async () => {
+    const app = createHonoApp({ kernel: kernelWithThrowingAuth(new Error(PLAIN)) as any, prefix: PREFIX, cors: false });
+    const answer = await send(app, 'GET', `${PREFIX}/auth/get-session`);
+    expect(answer.status, answer.text).toBe(500);
+    expect(answer.body).toEqual(kept(PLAIN));
+  });
+
+  it('the legacy dispatcher fallback (no auth service) throwing a driver diagnostic: withheld', async () => {
+    mockDispatcher.handleAuth.mockRejectedValueOnce(new Error(PROBE));
+    const app = createHonoApp({ kernel: { name: 'test-kernel' } as any, prefix: PREFIX, cors: false });
+    const answer = await send(app, 'POST', `${PREFIX}/auth/sign-in/email`);
+    expect(answer.status, answer.text).toBe(500);
+    expect(answer.body).toEqual(withheld);
+    expectNoDiagnostic(answer);
+  });
+});
diff --git a/packages/adapters/hono/src/index.ts b/packages/adapters/hono/src/index.ts
index 3529a20128d..446655b1e9b 100644
--- a/packages/adapters/hono/src/index.ts
+++ b/packages/adapters/hono/src/index.ts
@@ -529,11 +529,37 @@ export function createHonoApp(options: ObjectStackHonoOptions): Hono {
    * before: a bare `Error` is still `500` carrying `code` and `message`, with
    * no `cause`, and a throw declaring `statusCode` with no registered code
    * keeps that status.
+   *
+   * [#23532] …with one exception, the disclosure filter. That answer ships the
+   * thrown message, so this arm is a door emitting a thrown message, and it
+   * runs `looksLikeInternalErrorLeak` (`@objectstack/types`) exactly as the
+   * other such doors do: `HttpDispatcher.error`, `packages/rest`'s registrars,
+   * the recogniser's own 5xx limb above and this file's `/auth/config` arm.
+   * Without it a driver diagnostic reached the client verbatim. Measured
+   * through this host (an object registered, its table never synced):
+   *
+   *     POST /api/v1/data/ghost
+   *       500 {"success":false,"error":{"code":"INTERNAL_ERROR",
+   *            "message":"insert into [statement and bound values redacted] - no such table: ghost"}}
+   *
+   * Same scope as the twins: only a 5xx, because a 4xx message is a
+   * caller-facing answer by design, and only a message the predicate flags,
+   * so an ordinary bare `Error` still names itself. The replacement is the
+   * twins' `INTERNAL_ERROR_MESSAGE`, never a new literal. ⛔ This does not
+   * withhold every undeclared 5xx: whether an undeclared 5xx stays legible is
+   * a standing decision this arm does not reopen. The status and `code` are
+   * unchanged; only the message is replaced.
    */
   const thrownJson = (c: any, err: any) => {
     const declared = declaredEnvelopeForThrow(err);
     if (declared) return c.json(declared.body, declared.status);
-    return errorJson(c, err.message || 'Internal Server Error', err.statusCode || 500);
+    const status = err.statusCode || 500;
+    const message = err.message || 'Internal Server Error';
+    return errorJson(
+      c,
+      status >= 500 && looksLikeInternalErrorLeak(message) ? INTERNAL_ERROR_MESSAGE : message,
+      status,
+    );
   };
 
   const toResponse = (c: any, result: HttpDispatcherResult) => {