//! Tiny TCP-reachability probe for backend API endpoints.
//!
//! Used at startup to fail fast with a clear error when the
//! configured `shasta_base_url` isn't reachable, rather than
//! deferring the failure until the first real request.
use Duration;
use Error;
/// Timeout in seconds for the backend connectivity check.
const BACKEND_CONNECT_TIMEOUT_SECS: u64 = 3;
/// Verify that the backend API endpoint is reachable
/// (3-second connect timeout).
pub async