Function cross_layer_risk 

pub fn cross_layer_risk(findings: &[AuditFinding]) -> Vec<AuditFinding>

MAESTRO cross-layer compound-risk pass.

Collects the unique MAESTRO layers that carry a non-INFO finding; if ≥3 distinct layers are affected, emits SC-CROSS-001 (HIGH). The BTreeSet yields the layers already sorted, matching the TS Array.from(set).sort().