Function select_proton_askpass 

pub fn select_proton_askpass(
    target_askpass: &[Option<String>],
    default: Option<String>,
) -> Option<String>

Pick the askpass value that drives a single Proton Pass pre-flight call for a batch of hosts. Returns Some(value) if any host uses a proton: source (per-host override OR the global default), preferring the first proton: value by position in the slice before falling back to the default. Returns None when no host in the batch uses Proton Pass.