Function compare 

pub fn compare(
    view: &AuditAnalysesView<'_>,
    base: Option<&AuditKeySnapshot>,
    syntactic_fallback: bool,
) -> AuditComparison

Classify every head finding once against the base snapshot.

With syntactic_fallback set (the degraded type-aware path), dead code compares against the syntactic keys of the base, and a head finding that only semantic evidence produced stays advisory: it has no syntactic base counterpart to compare with.