```python
"""Melt a row of ice one simultaneous step at a time."""


def thaw_row(row: str, steps: int) -> str:
    if not isinstance(row, str) or not row:
        raise ValueError("thaw_row expects a non-empty string row")
    if not all(c in "#." for c in row):
        raise ValueError("row must contain only '#' and '.' characters")
    if not isinstance(steps, int) or steps < 0:
        raise ValueError("steps must be a non-negative integer")

    for _ in range(steps):
        new_row = list(row)
        for i in range(len(new_row)):
            if (i == 0 or new_row[i - 1] == ".") and new_row[i] == "#":
                new_row[i] = "."
            elif (i == len(new_row) - 1 or new_row[i + 1] == ".") and new_row[i] == "#":
                new_row[i] = "."
        row = "".join(new_row)

    return row
```