Function run_gate 

pub fn run_gate(
    baseline: &Report,
    current: &Report,
    tolerance: f64,
) -> GateResult

Gate a candidate report against a baseline. A metric regresses when current < baseline - tolerance. Configs are matched by their model label; a case regresses when it passed in the baseline but fails or is absent in the candidate.

A baseline and candidate recorded against different crate::Backends are never compared: a dropped case there could mean “the profile got worse” or just “this back-end’s capability envelope differs from that one” — those aren’t the same finding, and conflating them would make the gate lie about what regressed. This check is unconditional (no tolerance applies) and short- circuits before any per-config comparison runs.