Interface MetricStat

Mean (numbers) / fraction-true (booleans).

Number of runs the metric was observed in.

pass^k (τ-bench): 1 if the metric succeeded on EVERY trial, else 0. The reliability question a non-deterministic harness needs — "worked every time" is not "worked on average". A trial counts as a success when its value is truthy (booleans true, counts > 0), so model your metric as success/fail.

Standard error of the mean (std / √n).

Sample standard deviation (0 when n < 2).