```python
def code_sum(code: str) -> int:
    """Sum the digits in a code, ignoring non-digit characters."""
    return sum(int(char) for char in code if char.isdigit())

def good_codes(codes: list[str]) -> list[str]:
    """Return codes whose digit sum divides evenly by three."""
    return [code for code in codes if code_sum(code) % 3 == 0]
```