```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 isinstance(steps, int) or steps < 0:
        raise ValueError("thaw_row expects a non-negative integer step count")

    def melt_cell(cell):
        return "." if cell in ("#", ".") else None

    def is_meltwater(cell):
        return cell == "#"

    def can_melt(cell, left, right):
        return (
            (left is None or is_meltwater(left)) and
            (right is None or is_meltwater(right))
        )

    def melt_row(row):
        new_row = []
        for i in range(len(row)):
            if row[i] == "#":
                if can_melt(row[i], i - 1, i + 1):
                    new_row.append(melt_cell(row[i]))
                else:
                    new_row.append(".")
            else:
                new_row.append(row[i])
        return "".join(new_row)

    for _ in range(steps):
        row = melt_row(row)
    return row
```