🧭 fix: Subdirectory Deployment Auth Redirect Path Doubling (#12077)

* fix: subdirectory redirects

* fix: use path-segment boundary check when stripping BASE_URL prefix

A bare `startsWith(BASE_URL)` matches on character prefix, not path
segments. With BASE_URL="/chat", a path like "/chatroom/c/abc" would
incorrectly strip to "room/c/abc" (no leading slash). Guard with an
exact-match-or-slash check: `p === BASE_URL || p.startsWith(BASE_URL + '/')`.

Also removes the dead `BASE_URL !== '/'` guard — module init already
converts '/' to ''.

* test: add path-segment boundary tests and clarify subdirectory coverage

- Add /chatroom, /chatbot, /app/chatroom regression tests to verify
  BASE_URL stripping only matches on segment boundaries
- Clarify useAuthRedirect subdirectory test documents React Router
  basename behavior (BASE_URL stripping tested in api-endpoints-subdir)
- Use `delete proc.browser` instead of undefined assignment for cleanup
- Add rationale to eslint-disable comment for isolateModules require

* fix: use relative path and correct instructions in subdirectory test script

- Replace hardcoded /home/danny/LibreChat/.env with repo-root-relative
  path so the script works from any checkout location
- Update instructions to use production build (npm run build && npm run
  backend) since nginx proxies to :3080 which only serves the SPA after
  a full build, not during frontend:dev on :3090

* fix: skip pointless redirect_to=/ for root path and fix jsdom 26+ compat

buildLoginRedirectUrl now returns plain /login when the resolved path
is root — redirect_to=/ adds no value since / immediately redirects
to /c/new after login anyway.

Also rewrites api-endpoints.spec.ts to use window.history.replaceState
instead of Object.defineProperty(window, 'location', ...) which jsdom
26+ no longer allows.

* test: fix request-interceptor.spec.ts for jsdom 26+ compatibility

Switch from jsdom to happy-dom environment which allows
Object.defineProperty on window.location. jsdom 26+ made
location non-configurable, breaking all 8 tests in this file.

* chore: update browser property handling in api-endpoints-subdir test

Changed the handling of the `proc.browser` property from deletion to setting it to false, ensuring compatibility with the current testing environment.

* chore: update backend restart instructions in test subdirectory setup script

Changed the instruction for restarting the backend from "npm run backend:dev" to "npm run backend" to reflect the correct command for the current setup.

* refactor: ensure proper cleanup in loadModuleWithBase function

Wrapped the module loading logic in a try-finally block to guarantee that the `proc.browser` property is reset to false and the base element is removed, improving reliability in the testing environment.

* refactor: improve browser property handling in loadModuleWithBase function

Revised the management of the `proc.browser` property to store the original value before modification, ensuring it is restored correctly after module loading. This enhances the reliability of the testing environment.

packages/data-provider/specs/api-endpoints.spec.ts

@@ -4,18 +4,8 @@
 import { buildLoginRedirectUrl } from '../src/api-endpoints';
 
 describe('buildLoginRedirectUrl', () => {
-  let savedLocation: Location;
-
-  beforeEach(() => {
-    savedLocation = window.location;
-    Object.defineProperty(window, 'location', {
-      value: { pathname: '/c/abc123', search: '?model=gpt-4', hash: '#msg-5' },
-      writable: true,
-    });
-  });
-
   afterEach(() => {
-    Object.defineProperty(window, 'location', { value: savedLocation, writable: true });
+    window.history.replaceState({}, '', '/');
   });
 
   it('builds a login URL from explicit args', () => {
@@ -31,18 +21,16 @@ describe('buildLoginRedirectUrl', () => {
   });
 
   it('falls back to window.location when no args provided', () => {
+    window.history.replaceState({}, '', '/c/abc123?model=gpt-4#msg-5');
     const result = buildLoginRedirectUrl();
     const encoded = result.split('redirect_to=')[1];
     expect(decodeURIComponent(encoded)).toBe('/c/abc123?model=gpt-4#msg-5');
   });
 
-  it('falls back to "/" when all location parts are empty', () => {
-    Object.defineProperty(window, 'location', {
-      value: { pathname: '', search: '', hash: '' },
-      writable: true,
-    });
+  it('returns plain /login when all location parts are empty (root)', () => {
+    window.history.replaceState({}, '', '/');
     const result = buildLoginRedirectUrl();
-    expect(result).toBe('/login?redirect_to=%2F');
+    expect(result).toBe('/login');
   });
 
   it('returns plain /login when pathname is /login (prevents recursive redirect)', () => {
@@ -51,10 +39,7 @@ describe('buildLoginRedirectUrl', () => {
   });
 
   it('returns plain /login when window.location is already /login', () => {
-    Object.defineProperty(window, 'location', {
-      value: { pathname: '/login', search: '?redirect_to=%2Fc%2Fabc', hash: '' },
-      writable: true,
-    });
+    window.history.replaceState({}, '', '/login?redirect_to=%2Fc%2Fabc');
     const result = buildLoginRedirectUrl();
     expect(result).toBe('/login');
   });
@@ -65,10 +50,7 @@ describe('buildLoginRedirectUrl', () => {
   });
 
   it('returns plain /login for basename-prefixed /login (e.g. /librechat/login)', () => {
-    Object.defineProperty(window, 'location', {
-      value: { pathname: '/librechat/login', search: '?redirect_to=%2Fc%2Fabc', hash: '' },
-      writable: true,
-    });
+    window.history.replaceState({}, '', '/librechat/login?redirect_to=%2Fc%2Fabc');
     const result = buildLoginRedirectUrl();
     expect(result).toBe('/login');
   });
@@ -78,6 +60,12 @@ describe('buildLoginRedirectUrl', () => {
     expect(result).toBe('/login');
   });
 
+  it('returns plain /login for root path (no pointless redirect_to=/)', () => {
+    const result = buildLoginRedirectUrl('/', '', '');
+    expect(result).toBe('/login');
+    expect(result).not.toContain('redirect_to');
+  });
+
   it('does NOT match paths where "login" is a substring of a segment', () => {
     const result = buildLoginRedirectUrl('/c/loginhistory', '', '');
     expect(result).toContain('redirect_to=');