```python
def slot_pack(items: list, capacity: int) -> list:
    """Group items into slots of a fixed capacity, in order."""
    if not items or capacity <= 0:
        return []  # Handle empty input and zero capacity
    slots = []
    for i in range(0, len(items), capacity):
        if i + capacity > len(items):
            slots.append(items[i:])
        else:
            slots.append(items[i:i + capacity])
    return slots
```