feat(cabinet): recoverable "service unavailable" screen when the backend is unreachable

When the backend was down the cabinet got stuck on a blank loader: the bootstrap
token refresh used bare axios with no timeout (hung forever), and every
interceptor guard required an HTTP response — so a transport-level failure had
zero handling and no error UI ever appeared.

Add a full-screen ServiceUnavailableScreen (extends the existing blocking-store
pattern) shown whenever the backend is unreachable, that auto-recovers when it
returns:
- New 'backend_unavailable' blocking type + BlockingOverlay branch; mirrors
  MaintenanceScreen, CloudWarningIcon, i18n in ru/en/zh/fa.
- api/health.ts: pingBackend() probes the root /health/unified (bypasses the
  /api baseURL + interceptor); URL derived from the origin for remote/sub-path
  deploys; 502/503/504 count as down. reportPossibleBackendDown() confirms an
  outage with a liveness probe before flipping, so a one-off blip never blanks a
  loaded app.
- Detected from the response interceptor (no-response) and the bootstrap refresh
  path; doRefresh gets a timeout so it can no longer hang.
- A transport failure during refresh now PRESERVES the session (distinguished
  from a rejected token via lastFailureWasTransport) instead of logging the user
  out, so recovery actually resumes.
- Recovery lifts the overlay + refetches for an already-loaded session, and only
  hard-reloads when the initial bootstrap never reached the backend — no lost
  form state. Manual retry + 5s auto-poll. Dev proxy for /health.

src/App.tsx

@@ -28,6 +28,7 @@ import {
   ChannelSubscriptionScreen,
   BlacklistedScreen,
   AccountDeletedScreen,
+  ServiceUnavailableScreen,
 } from './components/blocking';
 import { ErrorBoundary } from './components/ErrorBoundary';
 import { PermissionRoute } from '@/components/auth/PermissionRoute';
@@ -232,6 +233,10 @@ function BlockingOverlay() {
     return <AccountDeletedScreen />;
   }
 
+  if (blockingType === 'backend_unavailable') {
+    return <ServiceUnavailableScreen />;
+  }
+
   return null;
 }
 

src/api/client.ts

@@ -7,6 +7,7 @@ import {
   safeRedirectToLogin,
 } from '../utils/token';
 import { useBlockingStore } from '../store/blocking';
+import { reportPossibleBackendDown, markBackendReached } from './health';
 import { API } from '../config/constants';
 
 const API_BASE_URL = import.meta.env.VITE_API_URL || '/api';
@@ -94,6 +95,12 @@ apiClient.interceptors.request.use(async (config: InternalAxiosRequestConfig) =>
       const newToken = await tokenRefreshManager.refreshAccessToken();
       if (newToken) {
         token = newToken;
+      } else if (tokenRefreshManager.lastFailureWasTransport) {
+        // Backend unreachable (not a rejected token): keep the session intact so
+        // the ServiceUnavailableScreen can auto-recover once the backend returns,
+        // instead of wiping tokens and stranding the user on /login. Let the
+        // request go out with the stale token; it will fail and be handled.
+        return config;
       } else {
         tokenStorage.clearTokens();
         safeRedirectToLogin();
@@ -195,10 +202,28 @@ export function isAccountDeletedError(
 }
 
 apiClient.interceptors.response.use(
-  (response) => response,
+  (response) => {
+    // First successful response means the app reached the backend at least once
+    // (it bootstrapped). Recovery from a later outage can then just lift the
+    // overlay instead of hard-reloading and losing unsaved UI state.
+    markBackendReached();
+    return response;
+  },
   async (error: AxiosError) => {
     const originalRequest = error.config as InternalAxiosRequestConfig & { _retry?: boolean };
 
+    // Transport-level failure: no HTTP response at all (backend unreachable, DNS
+    // failure, connection refused, timeout). All the coded guards below need
+    // `error.response`, so this case had zero handling and produced a blank
+    // screen during bootstrap. Confirm the outage with a liveness probe (so a
+    // one-off blip doesn't blank an already-loaded app) and, if confirmed, flip
+    // the full-screen ServiceUnavailableScreen. Fire-and-forget — the original
+    // request still rejects now. Axios cancellations are not outages.
+    if (!error.response && error.code !== 'ERR_CANCELED') {
+      void reportPossibleBackendDown();
+      return Promise.reject(error);
+    }
+
     if (isMaintenanceError(error)) {
       const detail = (error.response?.data as { detail: MaintenanceError }).detail;
       useBlockingStore.getState().setMaintenance({
@@ -256,6 +281,9 @@ apiClient.interceptors.response.use(
           originalRequest.headers.Authorization = `Bearer ${newToken}`;
         }
         return apiClient(originalRequest);
+      } else if (tokenRefreshManager.lastFailureWasTransport) {
+        // Backend died between the 401 and the refresh: keep the session so the
+        // ServiceUnavailableScreen can recover, rather than logging the user out.
       } else {
         tokenStorage.clearTokens();
         safeRedirectToLogin();

src/api/health.ts

@@ -0,0 +1,99 @@
+import axios from 'axios';
+import { useBlockingStore } from '../store/blocking';
+
+/**
+ * Backend liveness probe + "service unavailable" detection.
+ *
+ * The bot backend serves an unauthenticated liveness endpoint at the host ROOT
+ * (`/health/unified` when the Web API is enabled, `/health` otherwise) — NOT
+ * under the apiClient baseURL (`/api`). So we probe it with a BARE axios call at
+ * a root-relative URL, deliberately bypassing both the baseURL and the apiClient
+ * response interceptor (a probe must never itself touch blocking state).
+ */
+function resolveHealthUrl(): string {
+  const override = import.meta.env.VITE_HEALTH_URL;
+  if (override) return override;
+  const apiUrl = String(import.meta.env.VITE_API_URL || '/api').trim();
+  // For an absolute API base (remote / sub-path deployments like
+  // `https://api.bot.com/cabinet`) the health route still lives at the host
+  // ROOT, so derive the origin — NOT just strip `/api`. Mirrors the URL parsing
+  // in WebSocketProvider. For a relative base (`/api`, `/cabinet`) health is
+  // same-origin at the site root.
+  if (apiUrl.startsWith('http://') || apiUrl.startsWith('https://')) {
+    try {
+      return `${new URL(apiUrl).origin}/health/unified`;
+    } catch {
+      // malformed URL — fall through to the root-relative path
+    }
+  }
+  return '/health/unified';
+}
+
+export const HEALTH_URL = resolveHealthUrl();
+
+// Statuses a reverse proxy returns when it is up but its API upstream is down.
+// These must count as NOT reachable, otherwise the recovery poll would reload
+// the app straight back into a still-broken backend.
+const GATEWAY_DOWN_STATUSES = new Set([502, 503, 504]);
+
+/**
+ * Resolves true when the backend is actually serving — i.e. it returns an HTTP
+ * response that is NOT a gateway-down status. A 404 still counts as up (a
+ * Web-API-disabled deployment serves `/health`, not `/health/unified`, so
+ * probing the latter 404s while the server is fine). A 502/503/504 means a front
+ * proxy is up but the API upstream is dead, so it counts as NOT reachable.
+ * Resolves false on a transport-level failure with no response.
+ */
+export async function pingBackend(): Promise<boolean> {
+  try {
+    await axios.get(HEALTH_URL, { timeout: 5000 });
+    return true;
+  } catch (err) {
+    if (axios.isAxiosError(err) && err.response) {
+      return !GATEWAY_DOWN_STATUSES.has(err.response.status);
+    }
+    return false;
+  }
+}
+
+let everReachedBackend = false;
+
+/** Called on the first successful API response: the app reached the backend at
+ *  least once, so a later outage struck an already-loaded session. */
+export function markBackendReached(): void {
+  everReachedBackend = true;
+}
+
+/** True once the app has had at least one successful backend response. Lets the
+ *  ServiceUnavailableScreen recover by lifting the overlay (state preserved)
+ *  rather than hard-reloading, which is only needed when the INITIAL bootstrap
+ *  never reached the backend. */
+export function hasEverReachedBackend(): boolean {
+  return everReachedBackend;
+}
+
+let confirmInFlight = false;
+
+/**
+ * Called from the places that see a transport-level (no-response) failure — the
+ * apiClient interceptor and the bootstrap token refresh. Rather than blanking
+ * the whole app on a single one-off network blip, it CONFIRMS the outage with a
+ * liveness probe first and only then flips the global `backend_unavailable`
+ * state that renders the full-screen ServiceUnavailableScreen. Fire-and-forget:
+ * callers still reject/handle their own request immediately. Guarded so a burst
+ * of failing requests triggers at most one probe, and skipped once the screen is
+ * already shown.
+ */
+export async function reportPossibleBackendDown(): Promise<void> {
+  if (confirmInFlight) return;
+  if (useBlockingStore.getState().blockingType === 'backend_unavailable') return;
+  confirmInFlight = true;
+  try {
+    const reachable = await pingBackend();
+    if (!reachable) {
+      useBlockingStore.getState().setBackendUnavailable();
+    }
+  } finally {
+    confirmInFlight = false;
+  }
+}

src/components/blocking/ServiceUnavailableScreen.tsx

@@ -0,0 +1,156 @@
+import { useState, useEffect, useRef, useCallback } from 'react';
+import { useTranslation } from 'react-i18next';
+import { useQueryClient } from '@tanstack/react-query';
+import { useBlockingStore } from '../../store/blocking';
+import { useFocusTrap } from '../../hooks/useFocusTrap';
+import { pingBackend, hasEverReachedBackend } from '../../api/health';
+import { CloudWarningIcon, RestartIcon } from '@/components/icons';
+
+const POLL_INTERVAL_MS = 5000;
+
+/**
+ * Full-screen state shown when the backend is unreachable (transport-level
+ * failure), replacing the blank loader the app used to get stuck on. Polls the
+ * liveness endpoint and, once the backend answers again, reloads to re-bootstrap
+ * cleanly from whatever state the failed boot left behind. A manual retry button
+ * lets the user force an immediate check.
+ */
+export default function ServiceUnavailableScreen() {
+  const { t } = useTranslation();
+  const clearBlocking = useBlockingStore((state) => state.clearBlocking);
+  const queryClient = useQueryClient();
+  const [isChecking, setIsChecking] = useState(false);
+  const isCheckingRef = useRef(false);
+
+  const recover = useCallback(() => {
+    clearBlocking();
+    if (hasEverReachedBackend()) {
+      // The app was already loaded and merely covered by this overlay — its
+      // routes/forms are still mounted with their state. Lift the overlay and
+      // refetch instead of a hard reload that would discard unsaved input.
+      void queryClient.invalidateQueries();
+    } else {
+      // The initial bootstrap never reached the backend (blank loader) — reload
+      // to re-bootstrap cleanly now that it is back.
+      window.location.reload();
+    }
+  }, [clearBlocking, queryClient]);
+
+  // Manual retry: immediate probe with a visible checking state.
+  const handleRetry = useCallback(async () => {
+    if (isCheckingRef.current) return;
+    isCheckingRef.current = true;
+    setIsChecking(true);
+    try {
+      if (await pingBackend()) {
+        recover();
+      }
+    } finally {
+      isCheckingRef.current = false;
+      setIsChecking(false);
+    }
+  }, [recover]);
+
+  // Auto-recovery: probe immediately on mount, then every POLL_INTERVAL_MS.
+  useEffect(() => {
+    let cancelled = false;
+    const tick = async () => {
+      if (cancelled) return;
+      if (await pingBackend()) {
+        if (!cancelled) recover();
+      }
+    };
+    void tick();
+    const id = setInterval(tick, POLL_INTERVAL_MS);
+    return () => {
+      cancelled = true;
+      clearInterval(id);
+    };
+  }, [recover]);
+
+  const screenRef = useFocusTrap<HTMLDivElement>(true, { lockScroll: false });
+
+  return (
+    <div
+      ref={screenRef}
+      role="alertdialog"
+      aria-modal="true"
+      aria-labelledby="service-unavailable-title"
+      tabIndex={-1}
+      className="fixed inset-0 z-[100] flex flex-col items-center justify-center bg-dark-950 p-6"
+    >
+      <div className="w-full max-w-md text-center">
+        {/* Icon */}
+        <div className="mb-8">
+          <div className="mx-auto flex h-24 w-24 items-center justify-center rounded-full bg-dark-800">
+            <CloudWarningIcon className="h-12 w-12 text-warning-500" />
+          </div>
+        </div>
+
+        {/* Title */}
+        <h1 id="service-unavailable-title" className="mb-4 text-2xl font-bold text-white">
+          {t('blocking.serviceUnavailable.title')}
+        </h1>
+
+        {/* Message */}
+        <p className="mb-6 text-lg text-dark-400">{t('blocking.serviceUnavailable.description')}</p>
+
+        {/* Retry button */}
+        <button
+          onClick={handleRetry}
+          disabled={isChecking}
+          className="flex w-full items-center justify-center gap-3 rounded-xl bg-dark-800 px-6 py-4 font-semibold text-white transition-all duration-200 hover:bg-dark-700 disabled:bg-dark-800 disabled:opacity-60"
+        >
+          {isChecking ? (
+            <>
+              <svg
+                className="h-5 w-5 animate-spin"
+                xmlns="http://www.w3.org/2000/svg"
+                fill="none"
+                viewBox="0 0 24 24"
+              >
+                <circle
+                  className="opacity-25"
+                  cx="12"
+                  cy="12"
+                  r="10"
+                  stroke="currentColor"
+                  strokeWidth="4"
+                />
+                <path
+                  className="opacity-75"
+                  fill="currentColor"
+                  d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"
+                />
+              </svg>
+              {t('blocking.serviceUnavailable.checking')}
+            </>
+          ) : (
+            <>
+              <RestartIcon className="h-5 w-5" />
+              {t('blocking.serviceUnavailable.retry')}
+            </>
+          )}
+        </button>
+
+        {/* Decorative dots */}
+        <div className="mt-8 flex items-center justify-center gap-2">
+          <div
+            className="h-2 w-2 animate-pulse rounded-full bg-warning-500"
+            style={{ animationDelay: '0ms' }}
+          />
+          <div
+            className="h-2 w-2 animate-pulse rounded-full bg-warning-500"
+            style={{ animationDelay: '300ms' }}
+          />
+          <div
+            className="h-2 w-2 animate-pulse rounded-full bg-warning-500"
+            style={{ animationDelay: '600ms' }}
+          />
+        </div>
+
+        <p className="mt-4 text-sm text-dark-500">{t('blocking.serviceUnavailable.hint')}</p>
+      </div>
+    </div>
+  );
+}

src/components/blocking/index.ts

@@ -2,3 +2,4 @@ export { default as MaintenanceScreen } from './MaintenanceScreen';
 export { default as ChannelSubscriptionScreen } from './ChannelSubscriptionScreen';
 export { default as BlacklistedScreen } from './BlacklistedScreen';
 export { default as AccountDeletedScreen } from './AccountDeletedScreen';
+export { default as ServiceUnavailableScreen } from './ServiceUnavailableScreen';

src/components/icons/extended-icons.tsx

@@ -49,6 +49,7 @@ import {
   PiFlag,
   PiArrowCounterClockwise,
   PiArrowClockwise,
+  PiCloudWarning,
   PiRocket,
   PiFloppyDisk,
   PiPaperPlaneTilt,
@@ -361,6 +362,10 @@ export const RestartIcon = ({ className }: IconProps) => (
   <PiArrowClockwise className={cn('h-5 w-5', className)} />
 );
 
+export const CloudWarningIcon = ({ className }: IconProps) => (
+  <PiCloudWarning className={cn('h-5 w-5', className)} />
+);
+
 export const RocketIcon = ({ className }: IconProps) => (
   <PiRocket className={cn('h-5 w-5', className)} />
 );

src/locales/en.json

@@ -4810,6 +4810,13 @@
       "openBot": "Open the bot",
       "retry": "I pressed /start, retry",
       "hint": "After running /start, return here and tap «Retry»."
+    },
+    "serviceUnavailable": {
+      "title": "Service unavailable",
+      "description": "We can't reach the service right now. It may be undergoing maintenance or there's a temporary connection issue.",
+      "retry": "Try again",
+      "checking": "Checking connection...",
+      "hint": "This page will refresh automatically as soon as the service is back."
     }
   },
   "merge": {

src/locales/fa.json

@@ -4470,6 +4470,13 @@
       "openBot": "باز کردن ربات",
       "retry": "من /start را زدم، دوباره امتحان کن",
       "hint": "پس از اجرای /start، به اینجا بازگردید و «دوباره امتحان کنید» را بزنید."
+    },
+    "serviceUnavailable": {
+      "title": "سرویس در دسترس نیست",
+      "description": "در حال حاضر امکان اتصال به سرویس وجود ندارد. ممکن است در حال تعمیر باشد یا مشکل موقتی در اتصال وجود داشته باشد.",
+      "retry": "تلاش مجدد",
+      "checking": "در حال بررسی اتصال...",
+      "hint": "به‌محض در دسترس قرار گرفتن سرویس، این صفحه به‌طور خودکار بازخوانی می‌شود."
     }
   },
   "merge": {

src/locales/ru.json

@@ -5365,6 +5365,13 @@
       "openBot": "Открыть бота",
       "retry": "Я нажал /start, попробовать снова",
       "hint": "После /start вернитесь сюда и нажмите «Попробовать снова»."
+    },
+    "serviceUnavailable": {
+      "title": "Сервис недоступен",
+      "description": "Не удаётся подключиться к сервису. Возможно, идут технические работы или временные неполадки со связью.",
+      "retry": "Повторить попытку",
+      "checking": "Проверяем соединение...",
+      "hint": "Страница обновится автоматически, как только сервис снова станет доступен."
     }
   },
   "merge": {

src/locales/zh.json

@@ -4351,6 +4351,13 @@
       "openBot": "打开机器人",
       "retry": "我已按 /start，重试",
       "hint": "运行 /start 后，返回此处并点击「重试」。"
+    },
+    "serviceUnavailable": {
+      "title": "服务不可用",
+      "description": "暂时无法连接到服务。可能正在进行维护，或存在临时的网络问题。",
+      "retry": "重试",
+      "checking": "正在检查连接...",
+      "hint": "服务恢复后，本页面将自动刷新。"
     }
   },
   "banSystem": {

src/store/auth.ts

@@ -217,6 +217,11 @@ export const useAuthStore = create<AuthState>()(
                 const user = await authApi.getMe();
                 await get().checkAdminStatus();
                 applySession(newToken, refreshToken, user);
+              } else if (tokenRefreshManager.lastFailureWasTransport) {
+                // Backend unreachable, not a rejected token — keep the session
+                // (don't wipe tokens) so the ServiceUnavailableScreen can resume
+                // once the backend returns. Just stop the bootstrap loader.
+                set({ isLoading: false });
               } else {
                 clearSession();
               }
@@ -237,6 +242,11 @@ export const useAuthStore = create<AuthState>()(
                 } catch {
                   clearSession();
                 }
+              } else if (tokenRefreshManager.lastFailureWasTransport) {
+                // Backend unreachable, not a rejected token — keep the session
+                // (don't wipe tokens) so the ServiceUnavailableScreen can resume
+                // once the backend returns. Just stop the bootstrap loader.
+                set({ isLoading: false });
               } else {
                 clearSession();
               }

src/store/blocking.ts

@@ -5,6 +5,7 @@ export type BlockingType =
   | 'channel_subscription'
   | 'blacklisted'
   | 'account_deleted'
+  | 'backend_unavailable'
   | null;
 
 interface MaintenanceInfo {
@@ -54,6 +55,9 @@ interface BlockingState {
   setChannelSubscription: (info: ChannelSubscriptionInfo) => void;
   setBlacklisted: (info: BlacklistedInfo) => void;
   setAccountDeleted: (info: AccountDeletedInfo) => void;
+  /** Backend is unreachable (transport-level failure). Renders the full-screen
+   *  ServiceUnavailableScreen. No info payload — the screen shows static copy. */
+  setBackendUnavailable: () => void;
   clearBlocking: () => void;
 }
 
@@ -100,6 +104,15 @@ export const useBlockingStore = create<BlockingState>((set) => ({
       blacklistedInfo: null,
     }),
 
+  setBackendUnavailable: () =>
+    set({
+      blockingType: 'backend_unavailable',
+      maintenanceInfo: null,
+      channelInfo: null,
+      blacklistedInfo: null,
+      accountDeletedInfo: null,
+    }),
+
   clearBlocking: () =>
     set({
       blockingType: null,

src/utils/token.ts

@@ -5,6 +5,8 @@ import {
   deleteCloudStorageItem,
 } from '@telegram-apps/sdk-react';
 import { isInTelegramWebApp } from '../hooks/useTelegramSDK';
+import { API } from '../config/constants';
+import { reportPossibleBackendDown } from '../api/health';
 
 const TOKEN_KEYS = {
   ACCESS: 'access_token',
@@ -205,6 +207,17 @@ class TokenRefreshManager {
   private subscribers: ((token: string | null) => void)[] = [];
   private refreshEndpoint = '/api/cabinet/auth/refresh';
 
+  /**
+   * True when the most recent refresh failed at the TRANSPORT level (backend
+   * unreachable / timeout) rather than because the refresh token was rejected.
+   * Callers read this right after a null `refreshAccessToken()` to decide whether
+   * to destroy the session (rejected token) or KEEP it so the recoverable
+   * ServiceUnavailableScreen can resume once the backend returns. Synchronously
+   * accurate: it is set inside doRefresh before the shared promise resolves, so
+   * every awaiter (including deduped concurrent callers) reads a consistent value.
+   */
+  lastFailureWasTransport = false;
+
   setRefreshEndpoint(endpoint: string): void {
     this.refreshEndpoint = endpoint;
   }
@@ -214,6 +227,8 @@ class TokenRefreshManager {
       return this.refreshPromise;
     }
 
+    this.lastFailureWasTransport = false;
+
     const refreshToken = tokenStorage.getRefreshToken();
     if (!refreshToken) {
       return null;
@@ -238,7 +253,10 @@ class TokenRefreshManager {
       const response = await axios.post<{ access_token?: string }>(
         this.refreshEndpoint,
         { refresh_token: refreshToken },
-        { headers: { 'Content-Type': 'application/json' } },
+        // Without an explicit timeout this inherits axios's default of 0 (no
+        // timeout): on the persisted-token bootstrap path an unreachable backend
+        // would hang the refresh indefinitely, pinning the app on a blank loader.
+        { headers: { 'Content-Type': 'application/json' }, timeout: API.TIMEOUT_MS },
       );
 
       const newAccessToken = response.data.access_token;
@@ -249,7 +267,16 @@ class TokenRefreshManager {
       }
 
       return null;
-    } catch {
+    } catch (err) {
+      // This bare-axios call bypasses the apiClient interceptor, so a dead
+      // backend on the refresh-only bootstrap path would otherwise be swallowed
+      // here and silently fall through to a login redirect. Distinguish a
+      // transport-level failure (no response) from an invalid/expired token (a
+      // 4xx response) and surface the service-unavailable screen for the former.
+      if (axios.isAxiosError(err) && !err.response) {
+        this.lastFailureWasTransport = true;
+        void reportPossibleBackendDown();
+      }
       return null;
     }
   }

src/vite-env.d.ts

@@ -7,6 +7,8 @@ interface ImportMetaEnv {
   readonly VITE_TELEGRAM_BOT_USERNAME?: string;
   readonly VITE_APP_NAME?: string;
   readonly VITE_APP_LOGO?: string;
+  /** Optional override for the backend liveness URL (defaults to `<origin>/health/unified`). */
+  readonly VITE_HEALTH_URL?: string;
 }
 
 interface ImportMeta {