```python
import re

def parse_option(segment: str) -> list:
    """Parse a key=value segment into [key, value]."""
    match = re.match(r'^([a-zA-Z_][a-zA-Z0-9_]*)=(.*?)(;|$)', segment)
    if not match:
        raise ValueError("Invalid option format")
    key, value, _ = match.groups()
    if value.startswith('"') and not value.endswith('"'):
        raise ValueError("Unquoted value with missing closing quote")
    return [key, value.strip('"')]

def scan_pairs(text: str) -> list:
    """Split options string into pairs of [key, value]."""
    if not isinstance(text, str):
        raise ValueError("Input must be a string")
    if not text:
        return []
    
    result = []
    key_set = set()
    in_quotes = False
    current_segment = ""
    
    for char in text:
        if char == '"':
            in_quotes = not in_quotes
        elif char == ';' and not in_quotes:
            segment = current_segment.strip()
            if segment:
                parsed_pair = parse_option(segment)
                key, _ = parsed_pair
                if key in key_set:
                    raise ValueError("Repeated key")
                result.append(parsed_pair)
                key_set.add(key)
            current_segment = ""
        else:
            current_segment += char
    
    segment = current_segment.strip()
    if segment:
        parsed_pair = parse_option(segment)
        key, _ = parsed_pair
        if key in key_set:
            raise ValueError("Repeated key")
        result.append(parsed_pair)
    
    return result
```