use ;
/// Format an error with its full `source()` chain joined by `: `.
///
/// `Display` on most error types (notably `reqwest::Error` and
/// `tokio_tungstenite::Error`) only emits the top-level reason and discards
/// the underlying cause. That makes log output like "error sending request
/// for url (...)" useless for diagnosing whether it was DNS, TLS, a reset,
/// or a timeout. Walking the source chain restores the actionable detail.
pub