Function build_diff_context_locate 

pub fn build_diff_context_locate(
    root_dir: &Path,
    diff_range: Option<&str>,
    budget_tokens: Option<u32>,
    alpha: f64,
    tau: f64,
    scoring_mode: ScoringMode,
    timeout: u64,
) -> Result<LocateOutput>

--mode locate (#126): same heavy phase and the SAME selection as pack mode, rendered as a ranked navigation list with provenance reasons and no source bodies.