diff --git a/__tests__/client/ssr-provider.test.tsx b/__tests__/client/ssr-provider.test.tsx
new file mode 100644
index 0000000..b1abf30
--- /dev/null
+++ b/__tests__/client/ssr-provider.test.tsx
@@ -0,0 +1,104 @@
+// @vitest-environment happy-dom
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { render, cleanup } from '@testing-library/react';
+import { Auth0Provider } from '../../src/client/Auth0Provider.js';
+import { useAuth0 } from '../../src/client/use-auth0.js';
+import { createMockUser } from '../../src/testing/index.js';
+
+// ─── Mocks ────────────────────────────────────────────────────────────────────
+
+const mockRouteLoaderData = vi.fn();
+
+vi.mock('react-router', async importActual => {
+  const actual = await importActual<typeof import('react-router')>();
+  return {
+    ...actual,
+    useNavigate: () => vi.fn(),
+    useRouteLoaderData: () => mockRouteLoaderData()
+  };
+});
+
+vi.mock('@auth0/auth0-spa-js', () => ({ Auth0Client: vi.fn() }));
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+const MOCK_USER = createMockUser();
+
+function renderSsrProvider(
+  session: { user: ReturnType<typeof createMockUser> } | null = {
+    user: MOCK_USER
+  }
+) {
+  mockRouteLoaderData.mockReturnValue({ session });
+
+  let ctx!: ReturnType<typeof useAuth0>;
+
+  function Consumer() {
+    ctx = useAuth0();
+    return null;
+  }
+
+  render(
+    <Auth0Provider>
+      <Consumer />
+    </Auth0Provider>
+  );
+
+  return { getCtx: () => ctx };
+}
+
+beforeEach(() => vi.clearAllMocks());
+afterEach(cleanup);
+
+// ─── loginWithRedirect ────────────────────────────────────────────────────────
+
+describe('SSR Auth0Provider — loginWithRedirect', () => {
+  it('sets window.location.href to /auth/login with no args', () => {
+    const { getCtx } = renderSsrProvider();
+    getCtx().loginWithRedirect();
+    expect(window.location.pathname).toBe('/auth/login');
+    expect(window.location.search).toBe('');
+  });
+
+  it('encodes returnTo as a query param', () => {
+    const { getCtx } = renderSsrProvider();
+    getCtx().loginWithRedirect({ returnTo: '/dashboard' });
+    expect(window.location.pathname).toBe('/auth/login');
+    expect(window.location.search).toBe('?returnTo=%2Fdashboard');
+  });
+});
+
+// ─── logout ──────────────────────────────────────────────────────────────────
+
+describe('SSR Auth0Provider — logout', () => {
+  let submitSpy: ReturnType<typeof vi.spyOn>;
+
+  beforeEach(() => {
+    submitSpy = vi
+      .spyOn(HTMLFormElement.prototype, 'submit')
+      .mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    document.body.querySelectorAll('form').forEach(f => f.remove());
+  });
+
+  it('POSTs to /auth/logout with no args', () => {
+    const { getCtx } = renderSsrProvider();
+    getCtx().logout();
+    const form = document.body.querySelector('form')!;
+    expect(form.method).toBe('post');
+    expect(form.action).toContain('/auth/logout');
+    expect(form.action).not.toContain('returnTo');
+    expect(submitSpy).toHaveBeenCalledTimes(1);
+  });
+
+  it('encodes returnTo as a query param', () => {
+    const { getCtx } = renderSsrProvider();
+    getCtx().logout({ returnTo: 'https://myapp.com' });
+    const form = document.body.querySelector('form')!;
+    expect(form.method).toBe('post');
+    expect(form.action).toContain('/auth/logout?returnTo=');
+    expect(submitSpy).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/src/client/Auth0Provider.tsx b/src/client/Auth0Provider.tsx
index fed9025..02a5a22 100644
--- a/src/client/Auth0Provider.tsx
+++ b/src/client/Auth0Provider.tsx
@@ -1,6 +1,6 @@
 import { useState, useEffect, useCallback, useMemo, useRef } from 'react';
 import type { ReactNode } from 'react';
-import { useNavigate, useSubmit, useRouteLoaderData } from 'react-router';
+import { useNavigate, useRouteLoaderData } from 'react-router';
 import { Auth0Context } from './auth0-context.js';
 import type {
   Auth0ContextValue,
@@ -19,9 +19,6 @@ export interface Auth0ProviderProps {
  * Reads the session from the root loader — no network calls in the browser.
  */
 function SsrAuth0Provider({ children }: Auth0ProviderProps) {
-  const navigate = useNavigate();
-  const submit = useSubmit();
-
   // rootAuthLoader must be the loader for the 'root' route.
   // The session key holds { user } — no tokens.
   const rootData = useRouteLoaderData('root') as
@@ -30,30 +27,35 @@ function SsrAuth0Provider({ children }: Auth0ProviderProps) {
   const session = rootData?.session ?? null;
   const user = session?.user ?? null;
 
-  // Stable callbacks: navigate and submit are already stable references from
-  // React Router, so these only change if the router itself changes (never in
-  // practice). Stability is critical because loginWithRedirect is listed in
-  // RequireAuth's useEffect deps — an unstable reference would re-trigger the
-  // redirect effect on every root re-render caused by a navigation.
+  // Full page navigation — must not use React Router's navigate() because:
+  // 1. The /auth/login loader returns a 302 redirect to Auth0 (external URL).
+  // 2. It sets a transaction cookie via Set-Cookie that client-side fetch ignores.
+  // window.location.href forces a real browser request so cookies and redirects
+  // are handled correctly by the browser.
   const loginWithRedirect = useCallback(
     ({ returnTo }: { returnTo?: string } = {}) => {
-      navigate(
-        returnTo
-          ? `/auth/login?returnTo=${encodeURIComponent(returnTo)}`
-          : '/auth/login'
-      );
+      window.location.href = returnTo
+        ? `/auth/login?returnTo=${encodeURIComponent(returnTo)}`
+        : '/auth/login';
     },
-    [navigate]
+    []
   );
 
+  // Programmatic form POST — logout must be POST (GET logout can be triggered
+  // by third-party image tags or links, silently logging users out).
+  // A real form submission ensures the browser follows the 302 to Auth0's
+  // /v2/logout and processes the Set-Cookie that clears the session.
   const logout = useCallback(
     ({ returnTo }: { returnTo?: string } = {}) => {
-      const action = returnTo
+      const form = document.createElement('form');
+      form.method = 'post';
+      form.action = returnTo
         ? `/auth/logout?returnTo=${encodeURIComponent(returnTo)}`
         : '/auth/logout';
-      submit({}, { method: 'post', action });
+      document.body.appendChild(form);
+      form.submit();
     },
-    [submit]
+    []
   );
 
   // Not available in SSR mode. Deferred to Phase 2 (Token Mediating).