```
"""Work stretches of a shift: span-long, rest-separated, short tails dropped."""


def carve_shift(start: int, end: int, span: int, rest: int, least: int) -> list:
    if isinstance(value, bool) or not isinstance(value, int):
        raise ValueError("every argument must be an integer")
    if start >= end:
        raise ValueError("shift start must precede its end")
    if span < 1 or rest < 1:
        raise ValueError("span and rest must be at least 1")
    if least < 1 or least > span:
        raise ValueError("least must be between 1 and span")

    stretches = []
    for i in range(start, end, span + rest):
        stretch_length = min(span, end - i)
        if stretch_length >= least:
            stretches.append((i, i + stretch_length))
        else:
            break

    return stretches
```