Function merge_pending_outputs 

fn merge_pending_outputs(
    responses: Vec<PendingOutputs>,
    threshold: usize,
) -> PendingOutputs

Combines the guardians’ independent pending views into one, given the responses of the peers that answered and the federation’s threshold.

Kept free of any networking so the merge rules can be tested against synthetic responses: every integration test shares one bitcoin backend, so none of them ever sees guardians disagree.