Function derive_graph_facts 

pub fn derive_graph_facts(
    results: &AnalysisResults,
    closure: Option<&ImpactClosurePaths>,
) -> GraphFacts

Derive the Stage 1 graph facts from the analysis results plus the impact closure.

boundaries_touched is the deduped, sorted boundary-violation zone set; reachable_from is the impact closure’s affected-not-shown set (modules the changed code reaches / affects, none in the diff). exports_added / api_width_delta stay stubbed until the export-surface delta.