Your use-auth.tsx hook looks well-structured, but there are a few potential issues that could cause problems with session handling and JWT authentication. Here are some areas to check and debug:

🔍 Potential Issues and Fixes
1️⃣ LocalStorage Token Not Persisting or Fetching Correctly
Issue: The localStorage token may not be set correctly or retrieved before API requests.
Fix: Add a console.log(localStorage.getItem("auth_token")) before fetching the user.
tsx
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const token = localStorage.getItem('auth_token');
console.log("Retrieved Token:", token);
➡️ If null, the login function may not be storing it correctly.

2️⃣ Login Mutation May Not Be Setting JWT Correctly
Issue: Your loginMutation stores auth_token in localStorage, but some browsers block localStorage access in incognito/private mode.
Fix: Ensure the token is stored before calling queryClient.setQueryData and prefetchQuery.
Modify:

tsx
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const loginMutation = useMutation({
  mutationFn: async (credentials: LoginData) => {
    const res = await apiRequest("POST", "/api/login", credentials);
    if (!res.ok) {
      throw new Error("Login failed");
    }
    const data = await res.json();

    if (data.token) {
      console.log("Storing Token:", data.token);
      localStorage.setItem('auth_token', data.token);
    }

    return data;
  },
  onSuccess: (user: SelectUser) => {
    console.log("Login successful:", user);
    queryClient.setQueryData(["/api/user"], user);
  },
  onError: (error: Error) => {
    console.error("Login error:", error);
  },
});
➡️ This ensures the token is stored before React Query updates the state.

3️⃣ Logout Not Clearing Cache Correctly
Issue: queryClient.removeQueries({ queryKey: ["/api/user"] }) does not always trigger a re-render.
Fix: Explicitly set the query data to null before removing.
tsx
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const logoutMutation = useMutation({
  mutationFn: async () => {
    const res = await apiRequest("POST", "/api/logout");
    if (!res.ok) throw new Error("Logout failed");

    localStorage.removeItem('auth_token'); // Clear token
    queryClient.setQueryData(["/api/user"], null);
  },
  onSuccess: () => {
    console.log("User logged out successfully");
  },
});
➡️ This prevents stale session data after logout.

4️⃣ API Calls Not Sending Token Correctly
Issue: The Authorization header might not be set correctly when making fetch requests.
Fix: Ensure the token is included in every request.
Modify:

tsx
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const response = await fetch("/api/user", {
  headers: {
    'Authorization': token ? `Bearer ${token}` : '',
    'Content-Type': 'application/json',
  }
});
➡️ Ensure all API calls include the Authorization header.

5️⃣ React Query Cache Issues
Issue: After login/logout, queryClient might be holding stale data.
Fix: Force refetch after authentication events.
tsx
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queryClient.invalidateQueries(["/api/user"]);
➡️ Forces the user state to refresh.