Function build_focus_map 

pub fn build_focus_map(inputs: &FocusInputs<'_>) -> FocusMap

Build the weighted focus map from the assembled brief inputs: score each unit, label it (review-here / not-prioritized, NEVER skip), attach the reason and confidence flags, then partition into the ranked review_here list and the FULL deprioritized escape-hatch list.

Pure + deterministic: no timestamps, no randomness, integer arithmetic only, so two runs over the same tree produce a byte-identical focus map. The two output lists partition the unit set, so the escape-hatch completeness invariant (review_here.len() + deprioritized.len() == graph_facts.len()) holds by construction.