Function attribute_root_causes 

pub fn attribute_root_causes(
    episodes_out: &mut [DebugEpisode],
    episode_count: usize,
    eval_out: &[SignalEvaluation],
    num_signals: usize,
    num_windows: usize,
    service_graph: &[(u16, u16)],
    slew_delta: f64,
)

Walk the service-call graph and stamp each closed episode with its most-upstream contributing signal index, if determinable.

eval_out must be the same buffer that run_evaluation populated. service_graph is a slice of (parent_signal_idx, child_signal_idx) pairs. Empty graph → no attribution.