The Standard Library as Architecture

• SocketAddr, IpAddr, and newtypes encode transport identity without strings.
• tuples and small target structs accumulate typed context as a connection crosses stacks.
• Arc<T> shares immutable policy, TLS configs, metrics families, and retry budgets.
• HashMap stores routers, endpoints, caches, and label-indexed metrics.
• Duration makes queue, detection, idle, failfast, and request timeouts distinct.
• Option<T> and Conditional<T, Reason> distinguish absence from an explicitly disabled capability with a reason.
• Pin<Box<dyn Future + Send>> erases futures only where runtime storage requires it.
• RAII body wrappers observe end-of-stream or early drop to finish metrics and permits.

Newtypes are especially important: local versus remote addresses, server versus client TLS, logical versus concrete destinations, and inbound versus outbound labels are compile-time distinctions despite similar underlying data.