### Patch Plan

**1. `store.py`**
Modify `get_user` to apply the same normalization used in `save_user`.
```python
# Edit get_user(email):
def get_user(email):
    return USERS.get(email.strip().lower())
```

### Regression Test

```python
def test_login_normalization():
    # Setup
    email = " User@Example.com "
    pwd = "hashed_password"
    save_user(email, pwd)
    
    # Test: Login with original mixed-case/whitespace input
    assert login(email, pwd) is True
    # Test: Login with normalized input
    assert login("user@example.com", pwd) is True
```