```python
def fresh_value(entry: dict, now: int) -> str:
    if not isinstance(entry, dict) or len(entry) != 3:
        raise ValueError("Invalid record format")
    
    value, stored, ttl = entry.values()
    
    if not isinstance(value, str):
        raise ValueError("Value must be a string")
    if not isinstance(stored, int) or stored < 0:
        raise ValueError("Stored must be a non-negative integer")
    if not isinstance(ttl, int) or ttl <= 0:
        raise ValueError("TTL must be a positive integer")
    if not isinstance(now, int) or now < stored:
        raise ValueError("Now must be an integer at least stored")
    
    if stored + ttl <= now:
        raise ValueError("Record is no longer usable")
    
    return value
```