//! Back-end signal-handler installers.
//!
//! This module routes [`Coordinator::install`](crate::Coordinator::install)
//! to the right back-end at compile time, based on the active Cargo
//! features:
//!
//! | Feature | Back-end |
//! | ----------------- | -------------------------------------------------- |
//! | `tokio` | [`tokio_rt`] - `tokio::signal` + `tokio::spawn`. |
//! | `async-std` | [`async_std_rt`] - `signal-hook-async-std` + ctrlc.|
//! | `ctrlc-fallback` | [`ctrlc_sync`] - synchronous `ctrlc::set_handler`. |
//! | none of the above | [`Coordinator::install`] returns `Error::NoRuntime`. |
//!
//! `tokio` takes precedence over `async-std` when both are enabled.
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