```python
"""An installation order for packages under prerequisite pairs."""

from collections import deque

def install_order(packages: list, requires: list) -> list:
    if len(set(packages)) != len(packages):
        raise ValueError("Duplicate package names are not allowed.")
    
    for pkg, needed in requires:
        if pkg not in packages or needed not in packages:
            raise ValueError("Package name in requirement pair is absent from the list.")
    
    needs = {name: 0 for name in packages}
    enables = {name: [] for name in packages}
    for pkg, needed in requires:
        needs[pkg] += 1
        enables[needed].append(pkg)
    
    ready = deque(sorted(name for name in packages if needs[name] == 0))
    order = []
    while ready:
        next_name = ready.popleft()
        order.append(next_name)
        for follower in enables[next_name]:
            needs[follower] -= 1
            if needs[follower] == 0:
                ready.append(follower)
    
    if len(order) != len(packages):
        raise ValueError("Cycle detected in requirements.")
    
    return order
```