/// Only initializes a subscriber (and thus produces any log output at all)
/// when the caller opted in via `--log-level` — otherwise tracing's macros
/// are no-ops, leaving the terminal clean for the spinner.
pub(crate) fn initialize_observability(log_level: tracing::Level) {
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::try_from_default_env()
                .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new(log_level.to_string())),
        )
        .with_span_events(tracing_subscriber::fmt::format::FmtSpan::CLOSE)
        .with_writer(std::io::stderr)
        .init();
}