```python
def lap_best(laps: list) -> int:
    """The quickest completed lap of a session."""
    if not laps:
        return 0
    best = float('inf')
    for lap in laps:
        if lap > 0:  # Only consider positive lap times
            if lap < best:
                best = lap
    return best if best != float('inf') else 0
```