diff --git a/desktop/src/api/client.test.ts b/desktop/src/api/client.test.ts
index 35a4c3d1..7db7116e 100644
--- a/desktop/src/api/client.test.ts
+++ b/desktop/src/api/client.test.ts
@@ -1,11 +1,51 @@
 import { afterEach, describe, expect, it, vi } from 'vitest'
-import { api, rawRecordDiagnosticEvent } from './client'
+import {
+  api,
+  getDefaultBaseUrl,
+  rawRecordDiagnosticEvent,
+  setAuthToken,
+  setBaseUrl,
+} from './client'
 
 describe('api diagnostics reporting', () => {
   afterEach(() => {
+    setAuthToken(null)
+    setBaseUrl(getDefaultBaseUrl())
     vi.restoreAllMocks()
   })
 
+  it('does not send Authorization for default local requests', async () => {
+    const fetchMock = vi.spyOn(globalThis, 'fetch')
+    fetchMock.mockResolvedValueOnce(new Response(JSON.stringify({ ok: true }), {
+      status: 200,
+      headers: { 'Content-Type': 'application/json' },
+    }))
+
+    await api.get('/api/status')
+
+    const [, init] = fetchMock.mock.calls[0]!
+    expect((init as RequestInit).headers).toMatchObject({
+      'Content-Type': 'application/json',
+    })
+    expect((init as RequestInit & { headers?: Record<string, string> }).headers?.Authorization).toBeUndefined()
+  })
+
+  it('adds Authorization when an H5 token is configured', async () => {
+    const fetchMock = vi.spyOn(globalThis, 'fetch')
+    fetchMock.mockResolvedValueOnce(new Response(JSON.stringify({ ok: true }), {
+      status: 200,
+      headers: { 'Content-Type': 'application/json' },
+    }))
+
+    setAuthToken('h5_x')
+    await api.get('/api/status')
+
+    const [, init] = fetchMock.mock.calls[0]!
+    expect((init as RequestInit & { headers?: Record<string, string> }).headers).toMatchObject({
+      Authorization: 'Bearer h5_x',
+    })
+  })
+
   it('reports non-diagnostics API failures without request bodies', async () => {
     const fetchMock = vi.spyOn(globalThis, 'fetch')
     fetchMock
@@ -31,6 +71,27 @@ describe('api diagnostics reporting', () => {
     expect(JSON.stringify(body)).not.toContain('sk-should-not-report')
   })
 
+  it('does not leak the H5 token in diagnostics payloads', async () => {
+    const fetchMock = vi.spyOn(globalThis, 'fetch')
+    fetchMock
+      .mockResolvedValueOnce(new Response(JSON.stringify({ message: 'Unauthorized' }), {
+        status: 401,
+        headers: { 'Content-Type': 'application/json' },
+      }))
+      .mockResolvedValueOnce(new Response(JSON.stringify({ ok: true }), {
+        status: 200,
+        headers: { 'Content-Type': 'application/json' },
+      }))
+
+    setAuthToken('h5_super_secret')
+
+    await expect(api.get('/api/status')).rejects.toThrow('Unauthorized')
+
+    const [, diagnosticInit] = fetchMock.mock.calls[1]!
+    const body = JSON.parse(String((diagnosticInit as RequestInit).body))
+    expect(JSON.stringify(body)).not.toContain('h5_super_secret')
+  })
+
   it('does not recursively report diagnostics endpoint failures', async () => {
     const fetchMock = vi.spyOn(globalThis, 'fetch')
     fetchMock.mockResolvedValueOnce(new Response(JSON.stringify({ message: 'diagnostics down' }), {
diff --git a/desktop/src/api/client.ts b/desktop/src/api/client.ts
index 9d5c8207..efa1e090 100644
--- a/desktop/src/api/client.ts
+++ b/desktop/src/api/client.ts
@@ -8,6 +8,7 @@ const ENV_BASE_URL =
 const DEFAULT_BASE_URL = ENV_BASE_URL || 'http://127.0.0.1:3456'
 
 let baseUrl = DEFAULT_BASE_URL
+let authToken: string | null = null
 const DIAGNOSTICS_PATH = '/api/diagnostics/events'
 
 function getErrorMessage(status: number, body: unknown) {
@@ -30,6 +31,15 @@ export function getBaseUrl() {
   return baseUrl
 }
 
+export function setAuthToken(token: string | null) {
+  const trimmed = token?.trim() ?? ''
+  authToken = trimmed.length > 0 ? trimmed : null
+}
+
+export function getAuthToken() {
+  return authToken
+}
+
 export function getDefaultBaseUrl() {
   return DEFAULT_BASE_URL
 }
@@ -46,9 +56,7 @@ export class ApiError extends Error {
 
 async function request<T>(method: string, path: string, body?: unknown, options?: { timeout?: number }): Promise<T> {
   const url = `${baseUrl}${path}`
-  const headers: Record<string, string> = {
-    'Content-Type': 'application/json',
-  }
+  const headers = buildHeaders()
 
   const controller = new AbortController()
   const timeoutMs = options?.timeout ?? 30_000
@@ -88,12 +96,12 @@ function reportApiFailure(method: string, path: string, error: unknown) {
     method,
     path,
     errorName: error instanceof Error ? error.name : typeof error,
-    message: error instanceof Error ? error.message : String(error),
+    message: sanitizeDiagnosticValue(error instanceof Error ? error.message : String(error)),
   }
 
   if (error instanceof ApiError) {
     details.status = error.status
-    details.response = error.body
+    details.response = sanitizeDiagnosticValue(error.body)
   }
 
   void rawRecordDiagnosticEvent({
@@ -113,11 +121,43 @@ export function rawRecordDiagnosticEvent(event: {
 }) {
   return fetch(`${baseUrl}${DIAGNOSTICS_PATH}`, {
     method: 'POST',
-    headers: { 'Content-Type': 'application/json' },
+    headers: buildHeaders(),
     body: JSON.stringify(event),
   }).catch(() => undefined)
 }
 
+function buildHeaders(): Record<string, string> {
+  const headers: Record<string, string> = {
+    'Content-Type': 'application/json',
+  }
+
+  if (authToken) {
+    headers.Authorization = `Bearer ${authToken}`
+  }
+
+  return headers
+}
+
+function sanitizeDiagnosticValue(value: unknown): unknown {
+  if (!authToken) return value
+
+  if (typeof value === 'string') {
+    return value.split(authToken).join('[redacted]')
+  }
+
+  if (Array.isArray(value)) {
+    return value.map((entry) => sanitizeDiagnosticValue(entry))
+  }
+
+  if (value && typeof value === 'object') {
+    return Object.fromEntries(
+      Object.entries(value).map(([key, entry]) => [key, sanitizeDiagnosticValue(entry)]),
+    )
+  }
+
+  return value
+}
+
 export const api = {
   get: <T>(path: string, options?: { timeout?: number }) => request<T>('GET', path, undefined, options),
   post: <T>(path: string, body?: unknown, options?: { timeout?: number }) => request<T>('POST', path, body, options),
diff --git a/desktop/src/api/websocket.test.ts b/desktop/src/api/websocket.test.ts
index 7481319e..8cbead42 100644
--- a/desktop/src/api/websocket.test.ts
+++ b/desktop/src/api/websocket.test.ts
@@ -1,10 +1,16 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
-vi.mock('./client', () => ({
-  getBaseUrl: () => 'http://127.0.0.1:3456',
+const clientMocks = vi.hoisted(() => ({
+  baseUrl: 'http://127.0.0.1:3456',
+  authToken: null as string | null,
 }))
 
-import { wsManager } from './websocket'
+vi.mock('./client', () => ({
+  getBaseUrl: () => clientMocks.baseUrl,
+  getAuthToken: () => clientMocks.authToken,
+}))
+
+import { buildSessionWebSocketUrl, wsManager } from './websocket'
 
 type SocketHandler = (() => void) | ((event: { data: string }) => void)
 
@@ -53,6 +59,8 @@ describe('wsManager reconnect buffering', () => {
 
   beforeEach(() => {
     vi.useFakeTimers()
+    clientMocks.baseUrl = 'http://127.0.0.1:3456'
+    clientMocks.authToken = null
     FakeWebSocket.instances = []
     globalThis.WebSocket = FakeWebSocket as unknown as typeof WebSocket
     wsManager.disconnectAll()
@@ -89,4 +97,21 @@ describe('wsManager reconnect buffering', () => {
       JSON.stringify({ type: 'user_message', content: 'queued while offline' }),
     ])
   })
+
+  it('builds websocket URLs from http and encodes token query params', () => {
+    clientMocks.baseUrl = 'http://10.0.0.2:3456'
+    clientMocks.authToken = 'h5 token/with?chars'
+
+    expect(buildSessionWebSocketUrl('session-reconnect')).toBe(
+      'ws://10.0.0.2:3456/ws/session-reconnect?token=h5+token%2Fwith%3Fchars',
+    )
+  })
+
+  it('upgrades https backends to wss', () => {
+    clientMocks.baseUrl = 'https://remote.example.com'
+
+    expect(buildSessionWebSocketUrl('secure-session')).toBe(
+      'wss://remote.example.com/ws/secure-session',
+    )
+  })
 })
diff --git a/desktop/src/api/websocket.ts b/desktop/src/api/websocket.ts
index 2e10622b..aff11dbc 100644
--- a/desktop/src/api/websocket.ts
+++ b/desktop/src/api/websocket.ts
@@ -1,5 +1,5 @@
 import type { ClientMessage, ServerMessage } from '../types/chat'
-import { getBaseUrl } from './client'
+import { getAuthToken, getBaseUrl } from './client'
 
 type MessageHandler = (msg: ServerMessage) => void
 
@@ -39,8 +39,7 @@ class WebSocketManager {
       return
     }
 
-    const wsUrl = getBaseUrl().replace(/^http/, 'ws')
-    const ws = new WebSocket(`${wsUrl}/ws/${sessionId}`)
+    const ws = new WebSocket(buildSessionWebSocketUrl(sessionId))
 
     const conn: Connection = {
       ws,
@@ -178,4 +177,19 @@ class WebSocketManager {
   }
 }
 
+export function buildSessionWebSocketUrl(sessionId: string) {
+  const url = new URL(getBaseUrl())
+  url.protocol = url.protocol === 'https:' ? 'wss:' : 'ws:'
+  url.pathname = `/ws/${encodeURIComponent(sessionId)}`
+
+  const token = getAuthToken()
+  if (token) {
+    url.searchParams.set('token', token)
+  } else {
+    url.searchParams.delete('token')
+  }
+
+  return url.toString()
+}
+
 export const wsManager = new WebSocketManager()
diff --git a/desktop/src/components/layout/AppShell.test.tsx b/desktop/src/components/layout/AppShell.test.tsx
index 171c1a45..ded1fee4 100644
--- a/desktop/src/components/layout/AppShell.test.tsx
+++ b/desktop/src/components/layout/AppShell.test.tsx
@@ -1,9 +1,10 @@
-import { render, screen, waitFor } from '@testing-library/react'
+import { fireEvent, render, screen, waitFor } from '@testing-library/react'
 import '@testing-library/jest-dom'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 const mocks = vi.hoisted(() => ({
   initializeDesktopServerUrl: vi.fn(),
+  isTauriRuntime: false,
   fetchAll: vi.fn(),
   restoreTabs: vi.fn(),
   connectToSession: vi.fn(),
@@ -15,7 +16,9 @@ const mocks = vi.hoisted(() => ({
 
 vi.mock('../../lib/desktopRuntime', () => ({
   initializeDesktopServerUrl: mocks.initializeDesktopServerUrl,
-  isTauriRuntime: () => false,
+  isTauriRuntime: () => mocks.isTauriRuntime,
+  isH5ConnectionRequiredError: (error: unknown) =>
+    error instanceof Error && error.name === 'H5ConnectionRequiredError',
 }))
 
 vi.mock('../../stores/settingsStore', () => ({
@@ -68,6 +71,16 @@ vi.mock('./TabBar', () => ({
   TabBar: () => <nav>tabs loaded</nav>,
 }))
 
+vi.mock('./H5ConnectionView', () => ({
+  H5ConnectionView: ({ error, onConnected }: { error?: string | null; onConnected: () => void }) => (
+    <div>
+      <div>h5 connection view</div>
+      <div>{error}</div>
+      <button type="button" onClick={onConnected}>retry h5 bootstrap</button>
+    </div>
+  ),
+}))
+
 vi.mock('../shared/Toast', () => ({
   ToastContainer: () => null,
 }))
@@ -81,6 +94,7 @@ import { AppShell } from './AppShell'
 describe('AppShell boot flow', () => {
   beforeEach(() => {
     vi.clearAllMocks()
+    mocks.isTauriRuntime = false
     mocks.initializeDesktopServerUrl.mockResolvedValue('http://127.0.0.1:3456')
     mocks.fetchAll.mockResolvedValue(undefined)
     mocks.restoreTabs.mockResolvedValue(undefined)
@@ -139,4 +153,54 @@ describe('AppShell boot flow', () => {
       expect(mocks.connectToSession).toHaveBeenCalledWith('session-1')
     })
   })
+
+  it('shows the H5 connection view in browser mode when startup needs H5 auth', async () => {
+    mocks.initializeDesktopServerUrl.mockRejectedValueOnce(
+      Object.assign(new Error('Enter your H5 token to continue.'), {
+        name: 'H5ConnectionRequiredError',
+        serverUrl: 'https://remote.example.com',
+      }),
+    )
+
+    render(<AppShell />)
+
+    expect(await screen.findByText('h5 connection view')).toBeInTheDocument()
+    expect(screen.getByText('Enter your H5 token to continue.')).toBeInTheDocument()
+    expect(screen.queryByText('app.serverFailed')).not.toBeInTheDocument()
+  })
+
+  it('retries bootstrap after a successful H5 connection', async () => {
+    mocks.initializeDesktopServerUrl
+      .mockRejectedValueOnce(
+        Object.assign(new Error('The saved H5 token is no longer valid.'), {
+          name: 'H5ConnectionRequiredError',
+          serverUrl: 'https://remote.example.com',
+        }),
+      )
+      .mockResolvedValueOnce('https://remote.example.com')
+
+    render(<AppShell />)
+
+    expect(await screen.findByText('h5 connection view')).toBeInTheDocument()
+    fireEvent.click(screen.getByRole('button', { name: 'retry h5 bootstrap' }))
+
+    await screen.findByText('sidebar loaded')
+    expect(mocks.initializeDesktopServerUrl).toHaveBeenCalledTimes(2)
+    expect(mocks.fetchAll).toHaveBeenCalledTimes(1)
+  })
+
+  it('keeps the Tauri startup error path unchanged', async () => {
+    mocks.isTauriRuntime = true
+    mocks.initializeDesktopServerUrl.mockRejectedValueOnce(
+      Object.assign(new Error('desktop server startup failed'), {
+        name: 'H5ConnectionRequiredError',
+        serverUrl: 'https://remote.example.com',
+      }),
+    )
+
+    render(<AppShell />)
+
+    expect(await screen.findByText('app.serverFailed')).toBeInTheDocument()
+    expect(screen.queryByText('h5 connection view')).not.toBeInTheDocument()
+  })
 })
diff --git a/desktop/src/components/layout/AppShell.tsx b/desktop/src/components/layout/AppShell.tsx
index 24be8f26..11147d9a 100644
--- a/desktop/src/components/layout/AppShell.tsx
+++ b/desktop/src/components/layout/AppShell.tsx
@@ -6,24 +6,39 @@ import { UpdateChecker } from '../shared/UpdateChecker'
 import { useSettingsStore } from '../../stores/settingsStore'
 import { useUIStore, type SettingsTab } from '../../stores/uiStore'
 import { useKeyboardShortcuts } from '../../hooks/useKeyboardShortcuts'
-import { initializeDesktopServerUrl, isTauriRuntime } from '../../lib/desktopRuntime'
+import {
+  H5ConnectionRequiredError,
+  initializeDesktopServerUrl,
+  isH5ConnectionRequiredError,
+  isTauriRuntime,
+} from '../../lib/desktopRuntime'
 import { TabBar } from './TabBar'
 import { StartupErrorView } from './StartupErrorView'
 import { useTabStore, SETTINGS_TAB_ID } from '../../stores/tabStore'
 import { useChatStore } from '../../stores/chatStore'
 import { useTranslation } from '../../i18n'
+import { H5ConnectionView } from './H5ConnectionView'
 
 export function AppShell() {
   const fetchSettings = useSettingsStore((s) => s.fetchAll)
   const sidebarOpen = useUIStore((s) => s.sidebarOpen)
   const [ready, setReady] = useState(false)
   const [startupError, setStartupError] = useState<string | null>(null)
+  const [h5StartupError, setH5StartupError] = useState<H5ConnectionRequiredError | null>(null)
+  const [bootstrapNonce, setBootstrapNonce] = useState(0)
   const t = useTranslation()
+  const tauriRuntime = isTauriRuntime()
 
   useEffect(() => {
     let cancelled = false
 
     const bootstrap = async () => {
+      if (!cancelled) {
+        setReady(false)
+        setStartupError(null)
+        setH5StartupError(null)
+      }
+
       try {
         await initializeDesktopServerUrl()
         await fetchSettings()
@@ -43,7 +58,13 @@ export function AppShell() {
         })().catch(() => {})
       } catch (error) {
         if (!cancelled) {
-          setStartupError(error instanceof Error ? error.message : String(error))
+          if (!tauriRuntime && isH5ConnectionRequiredError(error)) {
+            setH5StartupError(error)
+            setStartupError(null)
+          } else {
+            setStartupError(error instanceof Error ? error.message : String(error))
+            setH5StartupError(null)
+          }
           setReady(false)
         }
       }
@@ -54,11 +75,11 @@ export function AppShell() {
     return () => {
       cancelled = true
     }
-  }, [fetchSettings])
+  }, [bootstrapNonce, fetchSettings, tauriRuntime])
 
   // Listen for macOS native menu navigation events (About / Settings)
   useEffect(() => {
-    if (!isTauriRuntime()) return
+    if (!tauriRuntime) return
     let unlisten: (() => void) | undefined
     import('@tauri-apps/api/event')
       .then(({ listen }) =>
@@ -77,6 +98,16 @@ export function AppShell() {
 
   useKeyboardShortcuts()
 
+  if (!tauriRuntime && h5StartupError) {
+    return (
+      <H5ConnectionView
+        initialServerUrl={h5StartupError.serverUrl}
+        error={h5StartupError.message}
+        onConnected={() => setBootstrapNonce((value) => value + 1)}
+      />
+    )
+  }
+
   if (startupError) {
     return <StartupErrorView error={startupError} />
   }
diff --git a/desktop/src/components/layout/H5ConnectionView.tsx b/desktop/src/components/layout/H5ConnectionView.tsx
new file mode 100644
index 00000000..55b17164
--- /dev/null
+++ b/desktop/src/components/layout/H5ConnectionView.tsx
@@ -0,0 +1,84 @@
+import type { FormEvent } from 'react'
+import { useState } from 'react'
+import { saveAndVerifyH5Connection } from '../../lib/desktopRuntime'
+import { Button } from '../shared/Button'
+import { Input } from '../shared/Input'
+
+type H5ConnectionViewProps = {
+  initialServerUrl?: string | null
+  error?: string | null
+  onConnected: () => void
+}
+
+export function H5ConnectionView({
+  initialServerUrl,
+  error: initialError,
+  onConnected,
+}: H5ConnectionViewProps) {
+  const [serverUrl, setServerUrl] = useState(initialServerUrl ?? '')
+  const [token, setToken] = useState('')
+  const [error, setError] = useState(initialError ?? '')
+  const [submitting, setSubmitting] = useState(false)
+
+  const handleSubmit = async (event: FormEvent<HTMLFormElement>) => {
+    event.preventDefault()
+    setSubmitting(true)
+    setError('')
+
+    try {
+      await saveAndVerifyH5Connection(serverUrl, token)
+      onConnected()
+    } catch (submitError) {
+      setError(
+        submitError instanceof Error ? submitError.message : 'Unable to connect to the H5 server.',
+      )
+    } finally {
+      setSubmitting(false)
+    }
+  }
+
+  return (
+    <div className="h-screen flex items-center justify-center bg-[var(--color-surface)] px-6">
+      <section className="w-full max-w-md rounded-lg border border-[var(--color-border)] bg-[var(--color-surface-container-low)] p-6 shadow-[var(--shadow-md)]">
+        <div className="mb-5">
+          <h1 className="text-lg font-semibold text-[var(--color-text-primary)]">
+            Connect to H5 Access
+          </h1>
+          <p className="mt-2 text-sm text-[var(--color-text-secondary)]">
+            Enter the server URL and H5 access token from the desktop app.
+          </p>
+        </div>
+
+        <form className="space-y-4" onSubmit={handleSubmit}>
+          <Input
+            label="Server URL"
+            placeholder="https://chat.example.com"
+            value={serverUrl}
+            onChange={(event) => setServerUrl(event.target.value)}
+            autoComplete="url"
+            required
+          />
+          <Input
+            label="H5 Token"
+            type="password"
+            placeholder="h5_..."
+            value={token}
+            onChange={(event) => setToken(event.target.value)}
+            autoComplete="current-password"
+            required
+          />
+
+          {error ? (
+            <div className="rounded-lg border border-[var(--color-error)]/30 bg-[var(--color-error)]/8 px-3 py-2 text-sm text-[var(--color-error)]">
+              {error}
+            </div>
+          ) : null}
+
+          <Button type="submit" size="lg" className="w-full" loading={submitting}>
+            Connect
+          </Button>
+        </form>
+      </section>
+    </div>
+  )
+}
diff --git a/desktop/src/lib/desktopRuntime.ts b/desktop/src/lib/desktopRuntime.ts
index 630aec95..10c5c48a 100644
--- a/desktop/src/lib/desktopRuntime.ts
+++ b/desktop/src/lib/desktopRuntime.ts
@@ -1,28 +1,115 @@
-import { getDefaultBaseUrl, setBaseUrl } from '../api/client'
+import { api, getDefaultBaseUrl, setAuthToken, setBaseUrl } from '../api/client'
+
+export const H5_SERVER_URL_STORAGE_KEY = 'cc-haha-h5-server-url'
+export const H5_TOKEN_STORAGE_KEY = 'cc-haha-h5-token'
+
+type H5ConnectionFailureReason = 'missing-token' | 'invalid-token' | 'verify-failed'
+
+export type StoredH5Connection = {
+  serverUrl: string | null
+  token: string | null
+}
+
+export class H5ConnectionRequiredError extends Error {
+  readonly serverUrl: string
+  readonly reason: H5ConnectionFailureReason
+
+  constructor(message: string, serverUrl: string, reason: H5ConnectionFailureReason) {
+    super(message)
+    this.name = 'H5ConnectionRequiredError'
+    this.serverUrl = serverUrl
+    this.reason = reason
+  }
+}
 
 export function isTauriRuntime() {
   if (typeof window === 'undefined') return false
   return '__TAURI_INTERNALS__' in window || '__TAURI__' in window
 }
 
+export function isBrowserH5Runtime() {
+  return typeof window !== 'undefined' && !isTauriRuntime()
+}
+
+export function readStoredH5Connection(): StoredH5Connection {
+  if (typeof window === 'undefined') {
+    return { serverUrl: null, token: null }
+  }
+
+  try {
+    return {
+      serverUrl: normalizeServerUrl(window.localStorage.getItem(H5_SERVER_URL_STORAGE_KEY)),
+      token: normalizeToken(window.localStorage.getItem(H5_TOKEN_STORAGE_KEY)),
+    }
+  } catch {
+    return { serverUrl: null, token: null }
+  }
+}
+
+export function clearStoredH5Connection() {
+  if (typeof window !== 'undefined') {
+    try {
+      window.localStorage.removeItem(H5_SERVER_URL_STORAGE_KEY)
+      window.localStorage.removeItem(H5_TOKEN_STORAGE_KEY)
+    } catch {
+      // Ignore storage failures
+    }
+  }
+
+  setAuthToken(null)
+}
+
+export async function saveAndVerifyH5Connection(serverUrl: string, token: string) {
+  const normalizedServerUrl = normalizeServerUrl(serverUrl)
+  const normalizedToken = normalizeToken(token)
+
+  if (!normalizedServerUrl) {
+    throw new Error('Enter a valid server URL.')
+  }
+
+  if (!normalizedToken) {
+    throw new Error('Enter your H5 access token.')
+  }
+
+  setBaseUrl(normalizedServerUrl)
+  setAuthToken(normalizedToken)
+
+  try {
+    await waitForHealth(normalizedServerUrl)
+    await verifyH5Access()
+  } catch (error) {
+    setAuthToken(null)
+    throw normalizeH5VerificationError(error, normalizedServerUrl)
+  }
+
+  if (typeof window !== 'undefined') {
+    try {
+      window.localStorage.setItem(H5_SERVER_URL_STORAGE_KEY, normalizedServerUrl)
+      window.localStorage.setItem(H5_TOKEN_STORAGE_KEY, normalizedToken)
+    } catch {
+      // Ignore storage failures after a successful verification.
+    }
+  }
+
+  return normalizedServerUrl
+}
+
+export function isH5ConnectionRequiredError(error: unknown): error is H5ConnectionRequiredError {
+  return error instanceof H5ConnectionRequiredError
+}
+
 export async function initializeDesktopServerUrl() {
   const fallbackUrl = getDefaultBaseUrl()
-  const queryUrl =
-    typeof window !== 'undefined'
-      ? new URLSearchParams(window.location.search).get('serverUrl')
-      : null
-  const requestedUrl = queryUrl?.trim() || fallbackUrl
 
   if (!isTauriRuntime()) {
-    setBaseUrl(requestedUrl)
-    await waitForHealth(requestedUrl)
-    return requestedUrl
+    return initializeBrowserServerUrl(fallbackUrl)
   }
 
   try {
     const { invoke } = await import('@tauri-apps/api/core')
     const serverUrl = await invoke<string>('get_server_url')
     setBaseUrl(serverUrl)
+    setAuthToken(null)
     await waitForHealth(serverUrl)
     return serverUrl
   } catch (error) {
@@ -33,6 +120,42 @@ export async function initializeDesktopServerUrl() {
   }
 }
 
+async function initializeBrowserServerUrl(fallbackUrl: string) {
+  const queryUrl =
+    typeof window !== 'undefined'
+      ? new URLSearchParams(window.location.search).get('serverUrl')
+      : null
+  const stored = readStoredH5Connection()
+  const requestedUrl = normalizeServerUrl(queryUrl) ?? stored.serverUrl ?? fallbackUrl
+  const token = stored.token
+
+  setBaseUrl(requestedUrl)
+  setAuthToken(token)
+  await waitForHealth(requestedUrl)
+
+  if (!requiresH5Auth(requestedUrl)) {
+    return requestedUrl
+  }
+
+  if (!token) {
+    clearStoredH5Connection()
+    throw new H5ConnectionRequiredError(
+      'Enter your H5 token to continue.',
+      requestedUrl,
+      'missing-token',
+    )
+  }
+
+  try {
+    await verifyH5Access()
+  } catch (error) {
+    clearStoredH5Connection()
+    throw normalizeH5VerificationError(error, requestedUrl)
+  }
+
+  return requestedUrl
+}
+
 async function waitForHealth(serverUrl: string) {
   let lastError: unknown
 
@@ -54,7 +177,55 @@ async function waitForHealth(serverUrl: string) {
 
   throw new Error(
     lastError instanceof Error
-      ? `Local server healthcheck failed: ${lastError.message}`
-      : 'Local server healthcheck failed',
+      ? `Server healthcheck failed: ${lastError.message}`
+      : 'Server healthcheck failed',
+  )
+}
+
+async function verifyH5Access() {
+  await api.post<{ ok: true }>('/api/h5-access/verify')
+}
+
+function normalizeServerUrl(value: string | null | undefined) {
+  const trimmed = value?.trim()
+  if (!trimmed) return null
+
+  try {
+    return new URL(trimmed).toString().replace(/\/$/, '')
+  } catch {
+    return null
+  }
+}
+
+function normalizeToken(value: string | null | undefined) {
+  const trimmed = value?.trim()
+  return trimmed ? trimmed : null
+}
+
+function requiresH5Auth(serverUrl: string) {
+  try {
+    const hostname = new URL(serverUrl).hostname
+    return hostname !== '127.0.0.1' && hostname !== 'localhost' && hostname !== '::1'
+  } catch {
+    return false
+  }
+}
+
+function normalizeH5VerificationError(error: unknown, serverUrl: string) {
+  if (error instanceof H5ConnectionRequiredError) {
+    return error
+  }
+
+  if (error instanceof Error && error.message.startsWith('Server healthcheck failed')) {
+    return new Error(`Unable to reach ${serverUrl}. Check the server URL or network access.`)
+  }
+
+  const message =
+    error instanceof Error ? error.message : 'Unable to verify the H5 access token.'
+  const unauthorized = message.includes('401') || message.toLowerCase().includes('unauthorized')
+  return new H5ConnectionRequiredError(
+    unauthorized ? 'The saved H5 token is no longer valid.' : 'Unable to verify the H5 access token.',
+    serverUrl,
+    unauthorized ? 'invalid-token' : 'verify-failed',
   )
 }