local: the non-blocking resolver — tokio lookup_host replaces the blocking to_socket_addrs

- resolve_target + local_tcp_dial resolve via tokio::net::lookup_host
  (the blocking std resolver parked the pump on resolver latency —
  the review 003 S-1-adjacent residue); the module doc's blocking
  caveat retired
- semantics unchanged: the dial keeps its try-all-addresses loop, the
  egress keeps first-address (upstream parity)

Verification: cargo test --features local (15 suites green), clippy
--all-targets --all-features -D warnings clean, fmt clean.

src/local/mod.rs

@@ -30,7 +30,8 @@
 //!   the client-gone teardown.
 //!
 //! Resolution is the provider's job (ADR-012): domain targets/destinations
-//! resolve here, at the seam — the ssh `-D` semantic.
+//! resolve here, at the seam — the ssh `-D` semantic, via the
+//! non-blocking [`tokio::net::lookup_host`] resolver.
 
 use std::io::ErrorKind;
 use std::net::SocketAddr;
@@ -49,19 +50,22 @@ use crate::{
 
 /// Resolve a [`TargetAddr`] to a `SocketAddr` (egress-side DNS; the
 /// ssh `-D` semantic — ADR-012: resolution is the provider's job). IP
-/// targets resolve directly; domain targets resolve via the blocking
-/// resolver (`std::net::ToSocketAddrs` — the POC #2 `LocalEgress`
-/// shape; the first address wins).
-pub(crate) fn resolve_target(addr: &TargetAddr) -> Result<SocketAddr, EgressError> {
+/// targets resolve directly; domain targets resolve via
+/// [`tokio::net::lookup_host`] (the non-blocking resolver — review 003
+/// S-1's blocking-`to_socket_addrs` residue retired; the first address
+/// wins, upstream parity).
+pub(crate) async fn resolve_target(addr: &TargetAddr) -> Result<SocketAddr, EgressError> {
     match addr {
         TargetAddr::Ip(sa) => Ok(*sa),
         TargetAddr::Domain(domain, port) => {
-            use std::net::ToSocketAddrs;
-            (domain.as_str(), *port)
-                .to_socket_addrs()
+            let addrs = tokio::net::lookup_host((domain.as_str(), *port))
+                .await
                 .map_err(|e| EgressError::Unreachable(format!("resolve {domain}: {e}")))?
                 .next()
-                .ok_or_else(|| EgressError::Unreachable(format!("resolve {domain}: no addresses")))
+                .ok_or_else(|| {
+                    EgressError::Unreachable(format!("resolve {domain}: no addresses"))
+                })?;
+            Ok(addrs)
         }
     }
 }
@@ -96,13 +100,10 @@ pub fn tcp_dial() -> DialFn {
 async fn local_tcp_dial(target: TargetAddr) -> Result<TargetHandle, SocksDialError> {
     let addrs: Vec<SocketAddr> = match &target {
         TargetAddr::Ip(sa) => vec![*sa],
-        TargetAddr::Domain(domain, port) => {
-            use std::net::ToSocketAddrs;
-            (domain.as_str(), *port)
-                .to_socket_addrs()
-                .map_err(|e| SocksDialError::HostUnreachable(format!("resolve {domain}: {e}")))?
-                .collect()
-        }
+        TargetAddr::Domain(domain, port) => tokio::net::lookup_host((domain.as_str(), *port))
+            .await
+            .map_err(|e| SocksDialError::HostUnreachable(format!("resolve {domain}: {e}")))?
+            .collect(),
     };
     if addrs.is_empty() {
         return Err(SocksDialError::HostUnreachable(format!(
@@ -176,7 +177,7 @@ impl Egress for LocalEgress {
     fn send(&mut self, addr: TargetAddr, payload: Bytes) -> BoxFuture<'_, Result<(), EgressError>> {
         let sock = Arc::clone(&self.sock);
         Box::pin(async move {
-            let dest = resolve_target(&addr)?;
+            let dest = resolve_target(&addr).await?;
             sock.send_to(&payload, dest)
                 .await
                 .map(|_| ())