add apiFetch that checks for logout

frontend/src/auth/AuthProvider.tsx

@@ -3,6 +3,7 @@ import type { ReactNode } from "react";
 import type { User } from "../utils/types.ts";
 import { login as apiLogin, logout as apiLogout, getUser } from "../utils/api/users.ts";
 import { AuthContext } from "./AuthContext.ts";
+import {registerUnauthorizedHandler} from "../utils/api/client.ts";
 
 /**
  * Owns the single source of truth for the authenticated user. Everything that
@@ -36,6 +37,10 @@ const AuthProvider = ({ children }: { children: ReactNode }) => {
         setUser(null);
     }, []);
 
+    useEffect(() => {
+        registerUnauthorizedHandler(logout);
+    }, [logout]);
+
     return (
         <AuthContext.Provider value={{ user, loading, login, logout, refresh }}>
             {children}

frontend/src/utils/api/client.ts

@@ -6,9 +6,32 @@ class AuthError extends Error {
     constructor() { super("Not authenticated"); this.name = "AuthError"; }
 }
 
-const isThumbnailAvailable = async (thumbnailUrl: string): Promise<boolean> => {
-    const response = await fetch(thumbnailUrl, { credentials: 'include' });
-    return response.ok;
-};
+let onUnauthorized: (() => void) | null = null;
 
-export { API_URL, AuthError, isThumbnailAvailable };
+export function registerUnauthorizedHandler(handler: () => void) {
+    onUnauthorized = handler;
+}
+
+async function apiFetch<T>(url: string, options: RequestInit = {}): Promise<T> {
+    const response = await fetch(url, {
+        ...options,
+        credentials: 'include'
+    });
+
+    if (response.status == 401 || response.status == 403) {
+        onUnauthorized?.();
+        throw new AuthError();
+    }
+
+    if (!response.ok) {
+        const text = await response.text();
+        let message = text;
+        try { message = JSON.parse(text).message ?? text; } catch { /* not JSON, use raw text */ }
+        throw new Error(message || `Request failed: ${response.status}`);
+    }
+
+    const text = await response.text();
+    return text ? JSON.parse(text) : (undefined as T);
+}
+
+export { API_URL, AuthError };