diff --git a/.changeset/24773-oauth-register-refusal-status.md b/.changeset/24773-oauth-register-refusal-status.md
new file mode 100644
index 00000000000..2807da55eb4
--- /dev/null
+++ b/.changeset/24773-oauth-register-refusal-status.md
@@ -0,0 +1,12 @@
+---
+'@objectstack/plugin-auth': patch
+---
+
+fix(plugin-auth): a refused OAuth application registration answers the status the refusal declared, not 500 (#24773)
+
+Clause-②: no
+
+`POST /api/v1/auth/sys-oauth-application/register` answered most refusals from better-auth as `500 OAUTH_REGISTER_FAILED`. better-auth raises each refusal as an `APIError` whose HTTP status is the number `statusCode` (`400`) and the name `status` (`'BAD_REQUEST'`). The route read only a numeric `status`, so a named refusal fell through to 500. Two examples are a redirect URI the provider refuses, such as `http://localhost:4001/callback` on a `web` client (`invalid_redirect_uri`), and a request with no session (`UNAUTHORIZED`).
+
+- **Now.** The route answers the refusal's own status: `400` for the redirect-URI refusal and `401` for the missing session. The code stays `OAUTH_REGISTER_FAILED`, and `error.details.upstreamError` still carries the provider's discriminator (`invalid_redirect_uri`).
+- **Unchanged.** A throw that declares no status, such as a storage fault while the client is persisted, still answers `500`. The body-schema refusal keeps answering `400`. Which redirect URIs a client may register is unchanged: a `web` client still needs an `https` URI on a non-loopback host.
diff --git a/packages/plugins/plugin-auth/src/auth-plugin.ts b/packages/plugins/plugin-auth/src/auth-plugin.ts
index d313aef1f42..03e026deaed 100644
--- a/packages/plugins/plugin-auth/src/auth-plugin.ts
+++ b/packages/plugins/plugin-auth/src/auth-plugin.ts
@@ -29,7 +29,7 @@ import {
 } from '@objectstack/platform-objects/apps';
 import { SysOrganizationDetailPage, SysUserDetailPage } from '@objectstack/platform-objects/pages';
 import { PLATFORM_OWNER_EMAIL_ENV, resolvePlatformOwnerEmail, resolveTenancyPosture } from '@objectstack/types';
-import { inProcessSessionReadInput } from '@objectstack/types';
+import { inProcessSessionReadInput, resolveThrownHttpError } from '@objectstack/types';
 import { postureEnforcesWall, type OrgScopingEntitlement } from '@objectstack/spec/security';
 import type { AuthSessionApi, IDataEngine, IEmailService, II18nService, IObjectQLEngine, ISmsService } from '@objectstack/spec/contracts';
 import {
@@ -3624,7 +3624,17 @@ export class AuthPlugin implements Plugin {
             ...inProcessSessionReadInput(c.req.raw.headers),
           });
         } catch (err: any) {
-          const status = typeof err?.status === 'number' ? err.status : 500;
+          // [#24773] Answer the status the refusal DECLARED, by the repo's one
+          // rule for a thrown error's status (`resolveThrownHttpError`).
+          // better-call's `APIError` — every refusal better-auth raises —
+          // carries its status twice: as the NUMBER `statusCode` (400) and as
+          // the NAME `status` ('BAD_REQUEST'). This door used to read only a
+          // numeric `status`, so each named refusal answered 500 — an
+          // `invalid_redirect_uri` redirect URI, a request with no session
+          // (`UNAUTHORIZED`) — while the body-schema `ValidationError`, whose
+          // `status` is the number 400, answered 400 from the same door. A
+          // throw that declares no status is a server fault and stays 500.
+          const { status } = resolveThrownHttpError(err, 500);
           // better-auth's `body.error` is an arbitrary upstream string, so it
           // cannot be `error.code` — that field is a closed set (ADR-0112) and
           // an unbounded source defeats it. Keep the code ours and carry the
diff --git a/packages/plugins/plugin-auth/src/oauth-register-refusal-status.test.ts b/packages/plugins/plugin-auth/src/oauth-register-refusal-status.test.ts
new file mode 100644
index 00000000000..8b2336493fe
--- /dev/null
+++ b/packages/plugins/plugin-auth/src/oauth-register-refusal-status.test.ts
@@ -0,0 +1,203 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#24773] `POST /api/v1/auth/sys-oauth-application/register` answers a
+ * refused registration with the status the refusal DECLARED — a client error
+ * is a coded 4xx (`OAUTH_REGISTER_FAILED`, ADR-0112), never 500 — and a throw
+ * that declares no status stays 500.
+ *
+ * The defect, measured against the installed better-auth: every refusal
+ * better-auth raises is better-call's `APIError`, which carries its status
+ * twice — the NUMBER `statusCode` (400) and the NAME `status` ('BAD_REQUEST').
+ * The wrapper read only a numeric `status`, so each named refusal answered 500:
+ * an `http://localhost` redirect URI on a `web` client (the vendor's
+ * `invalid_redirect_uri`), and a request with no session (`UNAUTHORIZED`).
+ * The body-schema `ValidationError`, whose `status` IS the number 400, answered
+ * 400 from the same door — one door, two answers for the same class.
+ *
+ * This file pins the STATUS only. Which redirect URIs a client may register is
+ * the vendor's acceptance rule and is not changed here: the loopback refusals
+ * below are the vendor's own answer, used as the fixture's named-status
+ * refusal.
+ *
+ * Driven against REAL better-auth (the installed version, OIDC provider on)
+ * behind the plugin's REAL route registration on a real Hono app — the
+ * `in-process-session-renewal.pin.test.ts` harness: a real `AuthManager` over
+ * the shared in-memory engine. Each refusal asserts the ADR-0112 envelope
+ * (`code` + `status`), the vendor's discriminator in `details`, and that no
+ * `sys_oauth_application` row was written.
+ */
+
+import { describe, it, expect, vi, beforeAll, afterAll } from 'vitest';
+import { Hono } from 'hono';
+import { envelopeViolations } from '@objectstack/spec/api';
+import type { PluginContext } from '@objectstack/core';
+import { AuthManager } from './auth-manager';
+import { AuthPlugin } from './auth-plugin';
+import { createMemoryEngine } from './impersonation-bearer-rotation.test';
+
+const SECRET = 'test-secret-at-least-32-chars-long!!';
+const PASSWORD = 'S3cure!Passw0rd-24773';
+const EMAIL = 'owner.24773@example.com';
+const ORIGIN = 'http://localhost:3000';
+const BASE = '/api/v1/auth';
+const DOOR = '/sys-oauth-application/register';
+const CLIENTS = 'sys_oauth_application';
+
+const mockCtx = (): PluginContext =>
+  ({
+    registerService: vi.fn(),
+    getService: vi.fn((name: string) => (name === 'manifest' ? { register: vi.fn() } : undefined)),
+    getServices: vi.fn(() => new Map()),
+    hook: vi.fn(),
+    trigger: vi.fn(),
+    logger: { info: vi.fn(), error: vi.fn(), warn: vi.fn(), debug: vi.fn() },
+    getKernel: vi.fn(),
+  }) as unknown as PluginContext;
+
+let engine: ReturnType<typeof createMemoryEngine>;
+let manager: AuthManager;
+let app: Hono;
+let cookie: string;
+
+const clientRows = (): number => (engine.tables.get(CLIENTS) ?? []).length;
+
+const register = (body: unknown, withSession = true) =>
+  app.request(`${ORIGIN}${BASE}${DOOR}`, {
+    method: 'POST',
+    headers: { 'content-type': 'application/json', origin: ORIGIN, ...(withSession ? { cookie } : {}) },
+    body: JSON.stringify(body),
+  });
+
+type Answer = {
+  success: boolean;
+  data?: { client?: { client_id?: unknown } };
+  error?: { code: string; message: string; details?: { upstreamError?: string } };
+};
+
+/** The refusal envelope: ADR-0112 `code` + `status`, and nothing persisted. */
+async function expectRefused(res: Response, status: number, rowsBefore: number, upstreamError?: string) {
+  const body = (await res.json()) as Answer;
+  expect(res.status, JSON.stringify(body)).toBe(status);
+  expect(envelopeViolations(body)).toEqual([]);
+  expect(body.success).toBe(false);
+  expect(body.error?.code).toBe('OAUTH_REGISTER_FAILED');
+  if (upstreamError) expect(body.error?.details?.upstreamError).toBe(upstreamError);
+  expect(clientRows(), 'a refused registration wrote a client row').toBe(rowsBefore);
+}
+
+beforeAll(async () => {
+  vi.spyOn(console, 'warn').mockImplementation(() => {});
+  vi.spyOn(console, 'error').mockImplementation(() => {});
+
+  engine = createMemoryEngine();
+  manager = new AuthManager({
+    secret: SECRET,
+    baseUrl: ORIGIN,
+    dataEngine: engine,
+    plugins: { oidcProvider: true },
+  } as unknown as ConstructorParameters<typeof AuthManager>[0]);
+
+  const direct = (path: string, body: unknown) =>
+    manager.handleRequest(
+      new Request(`${ORIGIN}${BASE}${path}`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify(body),
+      }),
+    );
+  const signUp = await direct('/sign-up/email', { email: EMAIL, password: PASSWORD, name: 'Client Owner' });
+  expect(signUp.status, `sign-up: ${await signUp.clone().text()}`).toBe(200);
+  const signIn = await direct('/sign-in/email', { email: EMAIL, password: PASSWORD });
+  expect(signIn.status, `sign-in: ${await signIn.clone().text()}`).toBe(200);
+  const staged = signIn.headers.getSetCookie().find((c) => /(?:^|\.)session_token=/.test(c.split(';')[0]));
+  if (!staged) throw new Error('sign-in staged no session cookie');
+  cookie = staged.split(';')[0];
+
+  app = new Hono();
+  const ctx = mockCtx();
+  const plugin = new AuthPlugin({ secret: SECRET });
+  await plugin.init(ctx);
+  (plugin as unknown as { authManager: AuthManager }).authManager = manager;
+  (plugin as unknown as {
+    registerAuthRoutes(server: unknown, ctx: PluginContext): void;
+  }).registerAuthRoutes({ getRawApp: () => app, getPort: () => 0 }, ctx);
+});
+
+afterAll(() => vi.restoreAllMocks());
+
+describe('[#24773] precondition — the fixture refusal is a NAMED-status APIError', () => {
+  it('better-auth refuses a loopback redirect URI on a web client with status "BAD_REQUEST" / statusCode 400', async () => {
+    // Without this, a vendor that switched to a numeric `status` would let the
+    // pins below pass on the pre-fix wrapper too, and prove nothing.
+    const api = (await manager.getApi()) as unknown as {
+      createOAuthClient(input: unknown): Promise<unknown>;
+    };
+    const thrown = await api
+      .createOAuthClient({
+        body: { client_name: 'precondition', redirect_uris: ['http://localhost:4001/callback'], application_type: 'web' },
+        headers: new Headers({ cookie }),
+      })
+      .then(() => undefined, (e: unknown) => e as { name?: unknown; status?: unknown; statusCode?: unknown; body?: { error?: unknown } });
+    expect(thrown, 'the vendor accepted the fixture URI — nothing below is a refusal').toBeDefined();
+    expect(thrown?.name).toBe('APIError');
+    expect(thrown?.status).toBe('BAD_REQUEST');
+    expect(thrown?.statusCode).toBe(400);
+    expect(thrown?.body?.error).toBe('invalid_redirect_uri');
+  });
+});
+
+describe('[#24773] a refusal answers the status it declared, never 500', () => {
+  it('http://localhost redirect URI on a web client: 400 OAUTH_REGISTER_FAILED, invalid_redirect_uri', async () => {
+    const before = clientRows();
+    const res = await register({ name: 'Local Dev', redirectURLs: 'http://localhost:4001/callback', type: 'web' });
+    await expectRefused(res, 400, before, 'invalid_redirect_uri');
+  });
+
+  it('http://127.0.0.1 redirect URI on a web client: 400 OAUTH_REGISTER_FAILED, invalid_redirect_uri', async () => {
+    const before = clientRows();
+    const res = await register({ name: 'Local Dev', redirectURLs: 'http://127.0.0.1:4001/callback', type: 'web' });
+    await expectRefused(res, 400, before, 'invalid_redirect_uri');
+  });
+
+  it('no session: the vendor\'s UNAUTHORIZED answers 401 OAUTH_REGISTER_FAILED', async () => {
+    const before = clientRows();
+    const res = await register({ name: 'Anonymous', redirectURLs: 'https://app.example.com/callback' }, false);
+    await expectRefused(res, 401, before);
+  });
+
+  it('preserved: the body-schema refusal (numeric status) still answers 400', async () => {
+    const before = clientRows();
+    const res = await register({ name: 'Plain HTTP', redirectURLs: 'http://app.example.com/callback' });
+    await expectRefused(res, 400, before);
+  });
+});
+
+describe('[#24773] a throw that declares no status is a server fault: 500', () => {
+  it('a storage fault while persisting the client answers 500, not a client error', async () => {
+    const before = clientRows();
+    const insert = engine.insert;
+    engine.insert = async (name: string, data: unknown) => {
+      if (name === CLIENTS) throw new Error('storage fault (test)');
+      return insert(name, data);
+    };
+    try {
+      const res = await register({ name: 'Fault', redirectURLs: 'https://app.example.com/callback' });
+      await expectRefused(res, 500, before);
+    } finally {
+      engine.insert = insert;
+    }
+  });
+});
+
+describe('[#24773] control — an accepted registration', () => {
+  it('https redirect URI on a web client: 200 with the minted client, one row written', async () => {
+    const before = clientRows();
+    const res = await register({ name: 'Production', redirectURLs: 'https://app.example.com/callback', type: 'web' });
+    const body = (await res.json()) as Answer;
+    expect(res.status, JSON.stringify(body)).toBe(200);
+    expect(envelopeViolations(body)).toEqual([]);
+    expect(typeof body.data?.client?.client_id).toBe('string');
+    expect(clientRows()).toBe(before + 1);
+  });
+});