# Spec: stats

Module `src/stats.py`. Plain functions over a list of numbers. No third-party
dependencies; Python 3.8+ stdlib only.

## mean(values)

Returns the arithmetic mean as `float`. Raises `ValueError("empty")` on an
empty list.

## median(values)

Returns the median as `float` and does not mutate `values`.
- Odd length: the middle element.
- Even length: the mean of the two middle elements.
- Empty list: `ValueError("empty")`.

## describe(values)

Returns `{"count": int, "mean": float, "median": float}`.