Function propagate_inter 

pub fn propagate_inter(
    call_edges: &[CallEdgeFlow],
    summaries: &[RoutineFlowSummary],
) -> InterFlowResult

Propagate taint across call_edges using the supplied summaries. Each edge is resolved one hop against its callee summary; a direct self-call and a missing summary surface as FlowUnknownFact (R13).