Function honest_period_ns 

pub fn honest_period_ns(period_ns: f64, slowest_setup_slack_ns: f64) -> f64

The period a block must be built at, given the period it was measured at and the worst setup slack across every corner of that run. A block that met every corner keeps its period; one that missed gets the miss plus SLOW_CORNER_MARGIN, rounded UP to the 0.5 ns grid.

A slack reported as -0.00 is a miss smaller than the report’s resolution, not a pass, so the sign — not the magnitude — decides.