```python
from typing import List, Union

def field_mean(records: list, field: str) -> int:
    if not isinstance(field, str):
        raise ValueError("field must be a string")

    total_sum = 0
    count = 0

    for record in records:
        if field in record and isinstance(record[field], (int, float)):
            total_sum += record[field]
            count += 1

    if count == 0:
        return 0

    rounded_mean = total_sum // count
    return rounded_mean
```