Function clamp_lambda 

pub fn clamp_lambda(raw: f64) -> f64

Clamp raw into the documented [0.9, 1.0) range.

1.0 is preserved as-is — that signals “no decay” at the call site, matching the historical DEFAULT_LAMBDA. Values strictly below 0.9 snap up to 0.9; values strictly above 1.0 (or non-finite) fall back to the default so misconfiguration cannot cancel the bandit out.