Initial MUH app implementation

frontend/src/lib/session.tsx

@@ -0,0 +1,58 @@
+import {
+  createContext,
+  useContext,
+  useEffect,
+  useMemo,
+  useState,
+  type PropsWithChildren,
+} from "react";
+import { USER_STORAGE_KEY } from "./storage";
+import type { UserOption } from "./types";
+
+interface SessionContextValue {
+  user: UserOption | null;
+  setUser: (user: UserOption | null) => void;
+}
+
+const SessionContext = createContext<SessionContextValue>({
+  user: null,
+  setUser: () => undefined,
+});
+
+function loadStoredUser(): UserOption | null {
+  const raw = window.localStorage.getItem(USER_STORAGE_KEY);
+  if (!raw) {
+    return null;
+  }
+  try {
+    return JSON.parse(raw) as UserOption;
+  } catch {
+    return null;
+  }
+}
+
+export function SessionProvider({ children }: PropsWithChildren) {
+  const [user, setUserState] = useState<UserOption | null>(() => loadStoredUser());
+
+  useEffect(() => {
+    if (user) {
+      window.localStorage.setItem(USER_STORAGE_KEY, JSON.stringify(user));
+      return;
+    }
+    window.localStorage.removeItem(USER_STORAGE_KEY);
+  }, [user]);
+
+  const value = useMemo(
+    () => ({
+      user,
+      setUser: setUserState,
+    }),
+    [user],
+  );
+
+  return <SessionContext.Provider value={value}>{children}</SessionContext.Provider>;
+}
+
+export function useSession() {
+  return useContext(SessionContext);
+}