```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 steps < 0 or not isinstance(steps, int):
        raise ValueError("thaw_row expects a non-negative integer steps")
    if any(c not in "#." for c in row):
        raise ValueError("thaw_row expects a row containing only '#' and '.'")
    
    def melt_step(row):
        new_row = []
        for i in range(len(row)):
            if i == 0 or i == len(row) - 1 or row[i - 1] == "#" or row[i + 1] == "#":
                new_row.append(".")
            else:
                new_row.append(row[i])
        return new_row
    
    for _ in range(steps):
        row = melt_step(row)
    
    return "".join(row)
```