@@ -0,0 +1,23 @@
+---
+"@objectstack/plugin-auth": patch
+---
+
+The auth catch-all yields only a 404 that disclaims ownership — better-auth's own 404 answers can no longer be replaced by another route's
+
+`registerAuthRoutes` mounts one catch-all over the whole auth namespace (`rawApp.all(`${basePath}/*`)`), and since #4088 that catch-all is deliberately not terminal: when better-auth answers 404 it calls `next()` and lets whatever else matched answer instead. That yield is load-bearing — `plugin-hono-server` mounts `/auth/me/permissions` and `/auth/me/localization` from its own `kernel:ready` hook, and without it those two are reachable only when HonoServerPlugin happens to register first.
+
+What the yield could not express is **which** 404 may be handed on, because it had only the status to go on. So every 404 was yielded, including the ones that are better-auth's own answer on a path its router serves. Measured with the shipped handler on a real Hono app: add one broad downstream mount — `app.all('/api/v1/*', c => c.json({}))`, the shape a composition adds — and
+
+```
+POST /api/v1/auth/delete-user   ->  200  {}
+```
+
+where better-auth answered 404 because `user.deleteUser` is deliberately unconfigured. That route is not hypothetical: `auth-route-ledger.ts` carries it under the `disabled` disposition precisely because it is published and refused — and the same holds for every 404 a routed endpoint produces for a bad token, an unknown id, or an admin family the deployment does mount. Those answers were all up for grabs.
+
+The catch-all now asks better-auth's live instance whether it owns the path before it yields. The seam is `auth.api` — the same one `auth-route-ledger.conformance.test.ts` reads and the same one the `/admin/` dogfood sweep derives from, because there is no route table to enumerate by hand; matching mirrors better-call's own `createRouter` walk, including its `SERVER_ONLY` skip and its `:param` syntax. That skip is load-bearing rather than cosmetic: measured on the stock boot, the nine `/admin/oauth2/*` endpoints are in `auth.api` and every one carries `SERVER_ONLY: true`, so better-call never routes them — their 404 is an unrouted one and stays yieldable, because ownership is "does better-call route this", not "is it in `auth.api`". An ownership table that cannot be built answers "not owned", so an enumeration failure degrades to the previous behaviour rather than taking the #4088 surface down with it.
+
+**The mount is untouched.** It still claims exactly `${basePath}/*` and still forwards every request under it to better-auth. What narrowed is only which 404 may be handed on.
+
+**Upgrade note — a composition that mounts a route matching paths under the auth base path may see a 404 where it previously saw its own answer.** Affected: deployments that register a route which also matches `/api/v1/auth/...` — most often a broad wildcard over the API prefix — mounted *after* AuthPlugin. Before this release, any request to a path better-auth serves but answers 404 on (a switched-off capability, not an unknown path) was passed to that route and the caller received *its* response, commonly `200` with an empty object. From this release the caller receives better-auth's 404. Callers that treated such a response as success — `res.ok`, `status === 200`, "no error thrown" — will start seeing the refusal that was always the real answer; that is the point of the change, and the wire shape they now get is the one a deployment without the extra mount has always returned. Nothing to do if you mount no such route: paths better-auth does **not** own are yielded as before, so `/auth/me/permissions`, `/auth/me/localization` and any other sibling route under the auth prefix are unaffected in either registration order.
+
+**One carve-out to that sentence, measured and bounded.** A **trailing-slash or doubled-slash spelling of a path better-auth DOES own** — `/api/v1/auth/delete-user/`, `/api/v1/auth//sign-in/social` — is now claimed rather than yielded. better-call treats those spellings as unrouted (it refuses on a `//` and on trailing-slash parity before it looks the route up), while this ownership table strips the trailing slash and drops empty segments and so counts them as owned. On a composition with a broad downstream mount, such a spelling therefore answers better-auth's 404 instead of that mount's response. Only those two spellings, only of a path better-auth already owns, and only where such a mount exists: no route in this repo registers a spelling of that shape, and every genuinely unowned path — every `/auth/me/*` route included — is yielded exactly as it was. Aligning the table with better-call's own pre-checks is tracked as a follow-up rather than carried here.
@@ -60,7 +60,14 @@ async function mountCatchAll(owned: Record<string, () => Response>) {
             headers: { 'Content-Type': 'application/json' },
         });
     });
-    (plugin as any).authManager = { handleRequest };
+    // [#15417] The catch-all now asks the auth manager whether better-auth owns
+    // the path before it yields, so this stand-in has to answer that too — the
+    // fixture is a fake `AuthManager`, and this is part of the contract it
+    // stands in for. Ownership is derived from the SAME `owned` table above, so
+    // the file keeps meaning exactly what its title says: the paths better-auth
+    // does not own are the ones that get yielded.
+    const ownsRoute = async (req: Request) => Object.hasOwn(owned, new URL(req.url).pathname);
+    (plugin as any).authManager = { handleRequest, ownsRoute };
 
     const httpServer: any = { getRawApp: () => app, getPort: () => 0 };
     (plugin as any).registerAuthRoutes(httpServer, ctx);
 
@@ -0,0 +1,224 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #15417 — WHICH 404 the auth catch-all is allowed to yield.
+ *
+ * `auth-catchall-fallthrough.test.ts` (#4088) pins that the catch-all yields at
+ * all. This file pins the other edge: it may only yield a 404 that DISCLAIMS
+ * ownership. A 404 from a path better-auth's own router serves is its ANSWER —
+ * a switched-off capability — and handing that to the rest of the chain is how
+ * it comes back as somebody else's `200 {}`.
+ *
+ * ── The measurement this file exists for ────────────────────────────────────
+ *
+ * #15417 reported `POST /api/v1/auth/admin/<nonexistent>` answering `200 {}` on
+ * a cloud composition, with a nonexistent path as the control. Reproduced on a
+ * framework-side boot (`@objectstack/verify` + the showcase stack, both with
+ * better-auth's admin plugin off and on), that path answers **404** — bodyless,
+ * no content-type — so the framework does not produce the reported status on
+ * its own. What does produce it is the yield: register ONE broad downstream
+ * mount after the catch-all — `app.all('/api/v1/*', c => c.json({}))`, the
+ * shape a composition adds — and the same request comes back `200 {}`, because
+ * the catch-all handed it on and the wildcard answered.
+ *
+ * That is a framework-side defect regardless of who mounts the wildcard,
+ * because the request handed on need not be an unknown path at all:
+ * `delete-user` answers 404 by the ledger's `disabled` disposition, and so does
+ * every routed endpoint that 404s on a bad token or an unknown id. Those
+ * answers were all up for grabs. Confirmed end-to-end on the framework-side
+ * boot with the wildcard installed: `POST /api/v1/auth/delete-user` now
+ * answers 404 where the wildcard's `200 {}` used to stand.
+ *
+ * ⚠️ Ownership is "does better-call ROUTE this", not "is it in `auth.api`".
+ * Measured on the stock boot: the nine `/admin/oauth2/*` endpoints are in
+ * `auth.api` and every one carries `SERVER_ONLY: true`, so `createRouter` skips
+ * them and their 404 is an unrouted one — they stay yieldable, and the pin
+ * below says so.
+ *
+ * ── Why the fixture stubs better-auth, and what it does NOT stub ────────────
+ *
+ * Same seam as the #4088 file: `handleRequest` is a path table so the test
+ * controls exactly which paths the vendor claims, and the real
+ * `registerAuthRoutes` runs on a real Hono app so the assertions are about the
+ * shipped handler. The ownership decision is NOT stubbed — `ownsRoute` here
+ * runs the real `buildBetterAuthRouteOwnership` over a fake `auth.api`, so the
+ * matcher under test is the shipped one.
+ *
+ * The stub's 404 is `new Response(null, { status: 404 })` — bodyless, no
+ * content-type — because that is what better-call 1.4.0 really returns for an
+ * unrouted path (`dist/router.mjs`), and what the framework-side boot measured
+ * on the wire. The #4088 fixture's JSON 404 is a convenience of that file.
+ */
+
+import { describe, it, expect, vi } from 'vitest';
+import { Hono } from 'hono';
+import { AuthPlugin } from './auth-plugin';
+import { buildBetterAuthRouteOwnership } from './better-auth-route-ownership';
+import type { PluginContext } from '@objectstack/core';
+
+const BASE = '/api/v1/auth';
+
+/** What better-call returns for a path it does not route: bodyless, no content-type. */
+const unrouted404 = () => new Response(null, { status: 404, statusText: 'Not Found' });
+
+/**
+ * Mount the real route registration on a real Hono app.
+ *
+ * @param api      the fake `auth.api` the REAL ownership matcher reads
+ * @param answers  path -> Response for the paths better-auth answers
+ */
+async function mountCatchAll(
+  api: Record<string, { path: string; options: { method: string | string[] } }>,
+  answers: Record<string, () => Response>,
+) {
+  const app = new Hono();
+  const ctx: 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 any;
+
+  const plugin = new AuthPlugin({ secret: 'test-secret-at-least-32-chars-long!!' });
+  await plugin.init(ctx);
+
+  const ownership = buildBetterAuthRouteOwnership(api as any);
+  const handleRequest = vi.fn(async (req: Request) => {
+    const make = answers[new URL(req.url).pathname];
+    return make ? make() : unrouted404();
+  });
+  (plugin as any).authManager = {
+    handleRequest,
+    // The shipped matcher, over the fake table — only the endpoint-path
+    // derivation is inlined here (AuthManager's own is private).
+    ownsRoute: async (req: Request) =>
+      ownership.owns(req.method, new URL(req.url).pathname.slice(BASE.length)),
+  };
+
+  (plugin as any).registerAuthRoutes({ getRawApp: () => app, getPort: () => 0 }, ctx);
+  return { app, handleRequest };
+}
+
+/** The shape a composition adds: one wildcard over the whole API prefix. */
+const addDownstreamWildcard = (app: Hono) => app.all('/api/v1/*', (c) => c.json({}));
+
+describe('#15417: the catch-all yields only a 404 that disclaims ownership', () => {
+  it('does NOT yield a 404 from a path better-auth OWNS — even with a wildcard downstream', async () => {
+    // `delete-user` is published and answers 404 because `user.deleteUser` is
+    // deliberately unconfigured — `auth-route-ledger.ts`'s `disabled`
+    // disposition. That 404 is an ANSWER and must reach the caller.
+    const { app } = await mountCatchAll(
+      { deleteUser: { path: '/delete-user', options: { method: 'POST' } } },
+      { [`${BASE}/delete-user`]: () => new Response(null, { status: 404 }) },
+    );
+    addDownstreamWildcard(app);
+
+    const res = await app.request(`http://localhost${BASE}/delete-user`, { method: 'POST' });
+
+    expect(res.status).toBe(404);
+    expect(await res.text()).toBe('');
+  });
+
+  it('does not yield an owned 404 on a PARAMETERISED path either', async () => {
+    // `/callback/:id` is routed and parameterised; a 404 from it is an answer.
+    const { app } = await mountCatchAll(
+      { callback: { path: '/callback/:id', options: { method: 'GET' } } },
+      { [`${BASE}/callback/github`]: () => new Response(null, { status: 404 }) },
+    );
+    addDownstreamWildcard(app);
+
+    const res = await app.request(`http://localhost${BASE}/callback/github`);
+
+    expect(res.status).toBe(404);
+  });
+
+  it('DOES yield a SERVER_ONLY endpoint\'s 404 — better-call never routed it', async () => {
+    // Measured on the stock boot: all nine `/admin/oauth2/*` endpoints are in
+    // `auth.api` carrying `SERVER_ONLY: true`. `createRouter` skips them, so the
+    // 404 the wire sees is an unrouted one and yielding it is correct. Were the
+    // table to trust `auth.api` wholesale instead of mirroring that skip, this
+    // route would stop being yieldable and a composition serving it downstream
+    // would break.
+    const { app } = await mountCatchAll(
+      {
+        adminListOAuthResources: {
+          path: '/admin/oauth2/resources',
+          options: { method: 'GET', metadata: { SERVER_ONLY: true } },
+        },
+      } as any,
+      {},
+    );
+    app.get(`${BASE}/admin/oauth2/resources`, (c) => c.json({ from: 'sibling' }));
+
+    const res = await app.request(`http://localhost${BASE}/admin/oauth2/resources`);
+
+    expect(res.status).toBe(200);
+    expect(await res.json()).toEqual({ from: 'sibling' });
+  });
+
+  it('STILL yields a 404 from a path better-auth does not own — #4088 intact', async () => {
+    // The route plugin-hono-server mounts from its own kernel:ready hook, in
+    // the registration order that used to 404. Nothing may make this red.
+    const { app } = await mountCatchAll({ getSession: { path: '/get-session', options: { method: 'GET' } } }, {});
+    app.get(`${BASE}/me/permissions`, (c) => c.json({ authenticated: true, from: 'hono-plugin' }));
+
+    const res = await app.request(`http://localhost${BASE}/me/permissions`);
+
+    expect(res.status).toBe(200);
+    expect(await res.json()).toEqual({ authenticated: true, from: 'hono-plugin' });
+  });
+
+  it('an unknown tail with nothing downstream still answers better-auth\'s 404', async () => {
+    // The control the card could not run from outside. Unchanged by #15417:
+    // the framework already answered 404 here, and still does.
+    const { app } = await mountCatchAll({ getSession: { path: '/get-session', options: { method: 'GET' } } }, {});
+
+    const res = await app.request(`http://localhost${BASE}/admin/definitely-not-a-route-1989`, { method: 'POST' });
+
+    expect(res.status).toBe(404);
+  });
+
+  it('a path better-auth owns is not yielded even when the DOWNSTREAM route is specific', async () => {
+    // Precedence still favours the namespace owner (the #4088 file pins this
+    // for 2xx; here it is pinned for the vendor's own 404 answer).
+    const { app } = await mountCatchAll(
+      { deleteUser: { path: '/delete-user', options: { method: 'POST' } } },
+      { [`${BASE}/delete-user`]: () => new Response(null, { status: 404 }) },
+    );
+    app.post(`${BASE}/delete-user`, (c) => c.json({ hijacked: true }));
+
+    const res = await app.request(`http://localhost${BASE}/delete-user`, { method: 'POST' });
+
+    expect(res.status).toBe(404);
+    expect(await res.text()).toBe('');
+  });
+
+  it('ownership is per METHOD: the same path on a verb better-auth does not serve still yields', async () => {
+    const { app } = await mountCatchAll(
+      { listUsers: { path: '/admin/list-users', options: { method: 'GET' } } },
+      {},
+    );
+    app.post(`${BASE}/admin/list-users`, (c) => c.json({ from: 'sibling' }));
+
+    const res = await app.request(`http://localhost${BASE}/admin/list-users`, { method: 'POST' });
+
+    expect(res.status).toBe(200);
+    expect(await res.json()).toEqual({ from: 'sibling' });
+  });
+
+  it('still forwards to better-auth exactly once per request', async () => {
+    const { app, handleRequest } = await mountCatchAll(
+      { deleteUser: { path: '/delete-user', options: { method: 'POST' } } },
+      { [`${BASE}/delete-user`]: () => new Response(null, { status: 404 }) },
+    );
+    addDownstreamWildcard(app);
+    handleRequest.mockClear();
+
+    await app.request(`http://localhost${BASE}/delete-user`, { method: 'POST' });
+
+    expect(handleRequest).toHaveBeenCalledTimes(1);
+  });
+});
@@ -59,6 +59,10 @@ import {
 } from './auth-session-audit.js';
 import { SESSION_ERASURE_PATHS } from './session-tombstone.js';
 import { envelopeVendorAdminRefusal } from './vendor-admin-refusal-envelope.js';
+import {
+  buildBetterAuthRouteOwnership,
+  type BetterAuthRouteOwnership,
+} from './better-auth-route-ownership.js';
 import {
   ADMIN_SESSION_COOKIE_KEY,
   STOP_IMPERSONATING_PATH,
@@ -5380,6 +5384,45 @@ export class AuthManager {
     return response;
   }
 
+  /**
+   * [#15417] Does better-auth ROUTE this request — i.e. is the path one its own
+   * router owns, whatever it then answers?
+   *
+   * The auth catch-all yields the request to the rest of the Hono chain when
+   * better-auth answers 404 (#4088), and it needs this to tell the two very
+   * different 404s apart: "I do not serve this path" (yieldable — that is how
+   * `plugin-hono-server`'s `/auth/me/*` routes stay reachable in either
+   * registration order) from "I serve it and the answer is 404" (NOT yieldable
+   * — a disabled capability's refusal is an answer, and handing it to a
+   * downstream wildcard is how it becomes `200 {}`). The mechanism, the
+   * measurement and the matching rules live in
+   * `better-auth-route-ownership.ts`.
+   *
+   * Keyed on the live instance and rebuilt whenever that instance is replaced,
+   * so a re-created auth (config change, test re-boot) never answers from a
+   * stale table. Returns `false` — the yielding, pre-#15417 answer — for any
+   * request it cannot decide, so a failure to enumerate can never take the
+   * #4088 surface down with it.
+   */
+  async ownsRoute(request: Request): Promise<boolean> {
+    const endpointPath = this.betterAuthEndpointPath(request);
+    if (endpointPath === undefined) return false;
+    try {
+      const auth = await this.getOrCreateAuth();
+      if (this.routeOwnershipFor !== auth || !this.routeOwnership) {
+        this.routeOwnership = buildBetterAuthRouteOwnership((auth as any)?.api);
+        this.routeOwnershipFor = auth;
+      }
+      return this.routeOwnership.owns(request.method, endpointPath);
+    } catch {
+      return false;
+    }
+  }
+
+  /** Memoized `auth.api` ownership table, and the instance it was built from. */
+  private routeOwnership?: BetterAuthRouteOwnership;
+  private routeOwnershipFor?: unknown;
+
   /**
    * The better-auth endpoint path (`/admin/remove-user`) this request addresses,
    * or `undefined` when it is not under the configured `basePath`.