fix(cli): bind multi-worker load balancer to --host

The single-worker serve path honored --host, but run_multi_worker_serve
hardcoded the load balancer to 127.0.0.1. With --host 0.0.0.0 and
--workers >1 (the common Docker setup) the balancer bound loopback only,
so the mapped port was refused from outside the container. Bind the
balancer to the requested host. Workers stay on loopback and are reached
only by the balancer.

Fixes #336.

crates/obscura-cli/src/main.rs

@@ -336,7 +336,7 @@ async fn main() -> anyhow::Result<()> {
 
             if workers > 1 {
                 tracing::info!("{} worker processes", workers);
-                run_multi_worker_serve(port, workers, proxy, stealth, user_agent).await?;
+                run_multi_worker_serve(port, host, workers, proxy, stealth, user_agent).await?;
             } else {
                 obscura_cdp::start_with_full_serve_options(
                     port, &host, proxy, stealth, user_agent, allow_file_access, storage_dir,
@@ -372,6 +372,7 @@ async fn main() -> anyhow::Result<()> {
 
 async fn run_multi_worker_serve(
     port: u16,
+    host: String,
     workers: u16,
     proxy: Option<String>,
     stealth: bool,
@@ -406,9 +407,13 @@ async fn run_multi_worker_serve(
 
     tokio::time::sleep(tokio::time::Duration::from_millis(500)).await;
 
-    let addr = std::net::SocketAddr::from(([127, 0, 0, 1], port));
+    // Bind the load balancer to the requested host, not hardcoded loopback.
-    let listener = TcpListener::bind(&addr).await?;
+    // With --host 0.0.0.0 (e.g. in Docker) the single-worker path already binds
-    tracing::info!("Load balancer on port {}, {} workers", port, workers);
+    // all interfaces; the multi-worker balancer must too, or the mapped port is
+    // refused from outside the container (issue #336). Workers stay on loopback
+    // and are only reached by the balancer.
+    let listener = TcpListener::bind((host.as_str(), port)).await?;
+    tracing::info!("Load balancer on {}:{}, {} workers", host, port, workers);
 
     let mut next_worker: u16 = 0;