diff --git a/frontend/src/app/appState.tsx b/frontend/src/app/appState.tsx
index 004680b..0f3357d 100644
--- a/frontend/src/app/appState.tsx
+++ b/frontend/src/app/appState.tsx
@@ -1,5 +1,5 @@
 import React, { useContext, useEffect, useMemo, useReducer } from 'react';
-import { clearAuthToken, setAuthToken } from '../lib/apiClient';
+import { clearAuthToken, setAuthToken, setAuthRefreshHandlers } from '../lib/apiClient';
 import { ApiProvider } from './ApiContext';
 import { listTenants } from '../lib/apiClient';
 
@@ -209,6 +209,21 @@ const AppStateProvider: React.FC<{ children?: React.ReactNode }> = ({ children }
     }
   }, [state.tenant]);
 
+  useEffect(() => {
+    setAuthRefreshHandlers({
+      onRefreshSuccess: (token, payload) => {
+        dispatch({ type: 'TOKEN_REFRESH_SUCCESS', token, tenant: payload?.tenant ?? null });
+      },
+      onRefreshFailure: (error) => {
+        dispatch({ type: 'TOKEN_REFRESH_FAILURE', error: (error as Error)?.message || null });
+      },
+    });
+
+    return () => {
+      setAuthRefreshHandlers({});
+    };
+  }, [dispatch]);
+
   useEffect(() => {
     let abort = false;
 
diff --git a/frontend/src/app/useDocumentPreview.ts b/frontend/src/app/useDocumentPreview.ts
index b1655a4..1048bb4 100644
--- a/frontend/src/app/useDocumentPreview.ts
+++ b/frontend/src/app/useDocumentPreview.ts
@@ -104,7 +104,7 @@ const useDocumentPreview = ({
 
     const existing = documentLinks.get(documentId);
       const now = Date.now();
-      const expiresAt = Number.isFinite(existing?.expiresAt) ? Number(existing?.expiresAt) : null;
+      const expiresAt = existing?.expiresAt ?? null;
       if (!force && existing && (!expiresAt || expiresAt > now)) {
         return existing;
       }
diff --git a/frontend/src/asset_manager.ts b/frontend/src/asset_manager.ts
index b2c516a..f2fbd00 100644
--- a/frontend/src/asset_manager.ts
+++ b/frontend/src/asset_manager.ts
@@ -184,9 +184,7 @@ export const resolveDocumentAssetUrl = (
   const view = createAssetView(asset);
   const object = view.getPrimaryObject();
   const url = object?.url || view.getPrimaryUrl();
-  const expiresAt = Number.isFinite(object?.expires_at)
-    ? Number(object?.expires_at)
-    : resolveAssetExpiresAt(asset);
+  const expiresAt = object?.expires_at ?? resolveAssetExpiresAt(asset);
   const now = Date.now();
   if (url && (!expiresAt || expiresAt > now)) {
     return url;
@@ -242,7 +240,7 @@ class AssetManager {
     const isPrimarySatisfied = () => {
       const object = view.getObject(1);
       if (object?.url) {
-        const objectExpiresAt = Number.isFinite(object.expires_at) ? Number(object.expires_at) : null;
+        const objectExpiresAt = object.expires_at ?? null;
         if (!objectExpiresAt || objectExpiresAt > now) {
           return true;
         }
diff --git a/frontend/src/documents/DocumentSummarySection.tsx b/frontend/src/documents/DocumentSummarySection.tsx
index 258be49..62b30a7 100644
--- a/frontend/src/documents/DocumentSummarySection.tsx
+++ b/frontend/src/documents/DocumentSummarySection.tsx
@@ -495,7 +495,7 @@ const DocumentSummarySection: React.FC<DocumentSummarySectionProps> = ({
   const extraSummaryRows = useMemo(() => {
     const rows: DocumentSummaryRow[] = [];
     const currentVersionNumber = document?.current_version?.version_number;
-    if (Number.isFinite(currentVersionNumber)) {
+    if (currentVersionNumber != null) {
       rows.push({
         key: 'current-version',
         label: 'Current version',
diff --git a/frontend/src/documents/SelectionFloatingActions.tsx b/frontend/src/documents/SelectionFloatingActions.tsx
index b36a4b3..b4374e8 100644
--- a/frontend/src/documents/SelectionFloatingActions.tsx
+++ b/frontend/src/documents/SelectionFloatingActions.tsx
@@ -349,9 +349,7 @@ const SelectionFloatingActions: React.FC<SelectionFloatingActionsProps> = ({
 
   const documentCount = documentIdList.length;
   const folderCount = folderIdList.length;
-  const totalCount = Number.isFinite(selectionCount)
-    ? Number(selectionCount)
-    : documentCount + folderCount;
+  const totalCount = selectionCount ?? documentCount + folderCount;
 
   const selectedDocuments = useMemo<DocumentLike[]>(() => {
     if (!documentIdList.length || !(documentLookupMap instanceof Map)) {
diff --git a/frontend/src/lib/apiClient.ts b/frontend/src/lib/apiClient.ts
index a189f1f..93f0df1 100644
--- a/frontend/src/lib/apiClient.ts
+++ b/frontend/src/lib/apiClient.ts
@@ -12,7 +12,7 @@ import type {
   TenantSnippet,
   TagResponse,
 } from './apiTypes';
-import type { AxiosInstance } from 'axios';
+import type { AxiosError, AxiosInstance, InternalAxiosRequestConfig, AxiosRequestConfig } from 'axios';
 
 export const httpClient: Pick<AxiosInstance, 'get' | 'post' | 'patch' | 'delete' | 'defaults'> = {
   get: api.get.bind(api),
@@ -22,6 +22,22 @@ export const httpClient: Pick<AxiosInstance, 'get' | 'post' | 'patch' | 'delete'
   defaults: api.defaults,
 };
 
+type AuthAwareRequestConfig = InternalAxiosRequestConfig & {
+  _retry?: boolean;
+  skipAuthRefresh?: boolean;
+};
+
+type AuthRequestConfig = AxiosRequestConfig & {
+  skipAuthRefresh?: boolean;
+};
+type AuthRefreshHandlers = {
+  onRefreshSuccess?: (token: string, payload?: { tenant?: unknown }) => void;
+  onRefreshFailure?: (error: unknown) => void;
+};
+
+let refreshPromise: Promise<string> | null = null;
+let authRefreshHandlers: AuthRefreshHandlers = {};
+
 const normalizeNumber = (value: unknown): number | undefined => {
   const n = Number(value);
   return Number.isFinite(n) ? n : undefined;
@@ -168,7 +184,7 @@ export const performLogin = async (payload: Record<string, unknown>): Promise<un
 };
 
 export const refreshSession = async (): Promise<{ access_token?: string; tenant?: unknown }> => {
-  const { data } = await api.post('/auth/refresh');
+  const { data } = await api.post('/auth/refresh', undefined, { skipAuthRefresh: true } as AuthRequestConfig);
   return data as { access_token?: string; tenant?: unknown };
 };
 
@@ -277,6 +293,59 @@ export const clearAuthToken = () => {
   delete api.defaults.headers.common.Authorization;
 };
 
+export const setAuthRefreshHandlers = (handlers: AuthRefreshHandlers) => {
+  authRefreshHandlers = handlers;
+};
+
+const performTokenRefresh = async (): Promise<string> => {
+  if (refreshPromise) {
+    return refreshPromise;
+  }
+
+  refreshPromise = refreshSession()
+    .then((data) => {
+      const token = data?.access_token;
+      if (!token) {
+        throw new Error('Missing access token in refresh response');
+      }
+      setAuthToken(token);
+      authRefreshHandlers.onRefreshSuccess?.(token, { tenant: data?.tenant });
+      return token;
+    })
+    .catch((error) => {
+      authRefreshHandlers.onRefreshFailure?.(error);
+      throw error;
+    })
+    .finally(() => {
+      refreshPromise = null;
+    });
+
+  return refreshPromise;
+};
+
+api.interceptors.response.use(
+  (response) => response,
+  async (error: AxiosError) => {
+    const response = error.response;
+    const config = (error.config || {}) as AuthAwareRequestConfig;
+    if (!response || response.status !== 401 || config._retry || config.skipAuthRefresh) {
+      return Promise.reject(error);
+    }
+
+    config._retry = true;
+
+    try {
+      const token = await performTokenRefresh();
+      const headers = (config.headers ?? {}) as Record<string, unknown>;
+      headers.Authorization = `Bearer ${token}`;
+      config.headers = headers as AuthAwareRequestConfig['headers'];
+      return api(config);
+    } catch (refreshError) {
+      return Promise.reject(refreshError);
+    }
+  },
+);
+
 export type {
   DownloadLink,
   DocumentResponse,