def normalize_phone(phone: str) -> str:
    """Normalize phone number to a canonical 09XXXXXXXXX format for Iranian numbers.
    Handles +98, 0098, 9, and 09 prefixes by focusing on the last 10 digits.
    """
    if not phone:
        return ""
    
    # Remove all non-digit characters
    digits = "".join(filter(str.isdigit, phone))
    
    # If no digits are found, return the original string stripped of whitespace.
    # This handles cases like "abc" -> "abc", "   " -> ""
    if not digits:
        return phone.strip()
    
    # Standard Iranian mobile numbers end with 10 digits starting with '9'
    # Example: 9123456789. We want to normalize this to 09123456789.
    if len(digits) >= 10:
        suffix = digits[-10:]
        if suffix.startswith("9"):
            return "0" + suffix
        
    return digits