Function build_direction 

pub fn build_direction(
    focus: &FocusMap,
    out_of_diff_by_file: &FxHashMap<String, Vec<String>>,
    routing: &RoutingFacts,
) -> ReviewDirection

Build the review direction. The SPINE is the change itself: every reviewable focus unit (review_here + the deprioritized escape hatch), so the direction is never empty when there is code to review. Ownership routing is a LEFT-JOINED overlay for the optional expert field, NOT the spine: sourcing the work-list from routing made it empty on solo / author’s-own-PR changes (no one else to ask), which is exactly the cloud’s dominant case. Each unit carries its scoring_budget (the focus composite score) so a fan-out spends AI proportional to risk, its per-file out_of_diff consumers, and the concern_lens. Non-source churn is excluded. Units with out-of-diff consumers sort first (load-bearing definitions before mechanical churn), then by budget.