```python
from typing import List, Tuple

def pack_entries(entries: List[Tuple[str, str]]) -> str:
    if not isinstance(entries, list):
        raise ValueError("Input must be a list")
    
    def escape_value(value: str) -> str:
        return value.replace("\\", "\\\\").replace("=", "\\=").replace(";", "\\;")
    
    escaped_entries = [f"{escape_key(key)}={escape_value(value)}" for key, value in entries]
    return ";".join(escaped_entries)
```