Constant DEFAULT_KAPPA 

pub const DEFAULT_KAPPA: f64 = 1.0;

The default acquisition exploration coefficient κ in ĉ + κ·σ̂.

One residual standard deviation of optimism — the UCB member of the MFPI/UCB family the resume rule is drawn from. Larger κ thaws more uncertain trials; 0 thaws purely by predicted asymptote.