Function compute_baseline_envelope 

pub fn compute_baseline_envelope(
    healthy_data: &[f64],
    baseline_mean: &[f64],
    num_signals: usize,
    num_windows: usize,
    rho_out: &mut [f64],
)

Compute per-signal envelope radii (3σ) from healthy residuals.

Arguments

• healthy_data - raw healthy window data (row-major)
• baseline_mean - per-signal means (immutable)
• num_signals - signals per window
• num_windows - healthy windows
• rho_out - output buffer for envelope radii