```python
def fill_template(template: str, values: dict) -> str:
    """
    Fill template with values from dictionary.
    
    :param template: Literal text containing placeholders.
    :param values: Dictionary mapping placeholder names to their replacements.
    :return: Modified string with placeholders replaced by values.
    
    :raises ValueError: If template is not a string, if there are unmatched braces,
                       if a placeholder name is invalid or unknown, or if template
                       contains non-printable characters.
    """
    def parse_template(template):
        stack = []
        result = []
        for char in template:
            if char == '{' and len(stack) > 0:
                raise ValueError("Unmatched opening brace")
            elif char == '}':
                if not stack or stack[-1] != '{':
                    raise ValueError("Mismatched closing brace")
                placeholder_name = ''.join(result)
                result.clear()
                stack.pop()
                if placeholder_name not in values:
                    raise ValueError(f"Unknown placeholder: {placeholder_name}")
                result.append(values[placeholder_name])
            else:
                if len(stack) > 0 or char == ' ' or ord(char) < 32:
                    raise ValueError("Invalid character in template")
                result.append(char)
        if stack:
            raise ValueError("Unmatched opening brace")
        return ''.join(result)

    try:
        return parse_template(template)
    except (ValueError, TypeError) as e:
        raise ValueError(f"Template fill error: {e}")
```