```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(cell in "#." for cell in row):
        raise ValueError("row can only contain '#' 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 = []
        for i, cell in enumerate(row):
            if cell == ".":
                new_row.append(".")
            elif i == 0 or i == len(row) - 1 or row[i - 1] == "." or row[i + 1] == ".":
                new_row.append(".")
            else:
                new_row.append("#")
        row = "".join(new_row)

    return row
```