feat(network-proxy): add a SOCKS5 proxy with policy enforcement (#9803)

### Summary
- Adds an optional SOCKS5 listener via `rama-socks5`
- SOCKS5 is disabled by default and gated by config
- Reuses existing policy enforcement and blocked-request recording
- Blocks SOCKS5 in limited mode to prevent method-policy bypass
- Applies bind clamping to the SOCKS5 listener

### Config
New/used fields under `network_proxy`:
- `enable_socks5`
- `socks_url`
- `enable_socks5_udp`

### Scope
- Changes limited to `codex-rs/network-proxy` (+ `codex-rs/Cargo.lock`)

### Testing
```bash
cd codex-rs
just fmt
cargo test -p codex-network-proxy --offline

codex-rs/network-proxy/src/proxy.rs

@@ -3,6 +3,7 @@ use crate::config;
 use crate::http_proxy;
 use crate::network_policy::NetworkPolicyDecider;
 use crate::runtime::unix_socket_permissions_supported;
+use crate::socks5;
 use crate::state::NetworkProxyState;
 use anyhow::Context;
 use anyhow::Result;
@@ -61,8 +62,9 @@ impl NetworkProxyBuilder {
         let current_cfg = state.current_cfg().await?;
         let runtime = config::resolve_runtime(&current_cfg)?;
         // Reapply bind clamping for caller overrides so unix-socket proxying stays loopback-only.
-        let (http_addr, admin_addr) = config::clamp_bind_addrs(
+        let (http_addr, socks_addr, admin_addr) = config::clamp_bind_addrs(
             self.http_addr.unwrap_or(runtime.http_addr),
+            runtime.socks_addr,
             self.admin_addr.unwrap_or(runtime.admin_addr),
             &current_cfg.network_proxy,
         );
@@ -70,6 +72,7 @@ impl NetworkProxyBuilder {
         Ok(NetworkProxy {
             state,
             http_addr,
+            socks_addr,
             admin_addr,
             policy_decider: self.policy_decider,
         })
@@ -80,6 +83,7 @@ impl NetworkProxyBuilder {
 pub struct NetworkProxy {
     state: Arc<NetworkProxyState>,
     http_addr: SocketAddr,
+    socks_addr: SocketAddr,
     admin_addr: SocketAddr,
     policy_decider: Option<Arc<dyn NetworkPolicyDecider>>,
 }
@@ -105,10 +109,21 @@ impl NetworkProxy {
             self.http_addr,
             self.policy_decider.clone(),
         ));
+        let socks_task = if current_cfg.network_proxy.enable_socks5 {
+            Some(tokio::spawn(socks5::run_socks5(
+                self.state.clone(),
+                self.socks_addr,
+                self.policy_decider.clone(),
+                current_cfg.network_proxy.enable_socks5_udp,
+            )))
+        } else {
+            None
+        };
         let admin_task = tokio::spawn(admin::run_admin_api(self.state.clone(), self.admin_addr));
 
         Ok(NetworkProxyHandle {
             http_task: Some(http_task),
+            socks_task,
             admin_task: Some(admin_task),
             completed: false,
         })
@@ -117,6 +132,7 @@ impl NetworkProxy {
 
 pub struct NetworkProxyHandle {
     http_task: Option<JoinHandle<Result<()>>>,
+    socks_task: Option<JoinHandle<Result<()>>>,
     admin_task: Option<JoinHandle<Result<()>>>,
     completed: bool,
 }
@@ -125,6 +141,7 @@ impl NetworkProxyHandle {
     fn noop() -> Self {
         Self {
             http_task: Some(tokio::spawn(async { Ok(()) })),
+            socks_task: None,
             admin_task: Some(tokio::spawn(async { Ok(()) })),
             completed: true,
         }
@@ -133,33 +150,49 @@ impl NetworkProxyHandle {
     pub async fn wait(mut self) -> Result<()> {
         let http_task = self.http_task.take().context("missing http proxy task")?;
         let admin_task = self.admin_task.take().context("missing admin proxy task")?;
+        let socks_task = self.socks_task.take();
         let http_result = http_task.await;
         let admin_result = admin_task.await;
+        let socks_result = match socks_task {
+            Some(task) => Some(task.await),
+            None => None,
+        };
         self.completed = true;
         http_result??;
         admin_result??;
+        if let Some(socks_result) = socks_result {
+            socks_result??;
+        }
         Ok(())
     }
 
     pub async fn shutdown(mut self) -> Result<()> {
-        abort_tasks(self.http_task.take(), self.admin_task.take()).await;
+        abort_tasks(
+            self.http_task.take(),
+            self.socks_task.take(),
+            self.admin_task.take(),
+        )
+        .await;
         self.completed = true;
         Ok(())
     }
 }
 
+async fn abort_task(task: Option<JoinHandle<Result<()>>>) {
+    if let Some(task) = task {
+        task.abort();
+        let _ = task.await;
+    }
+}
+
 async fn abort_tasks(
     http_task: Option<JoinHandle<Result<()>>>,
+    socks_task: Option<JoinHandle<Result<()>>>,
     admin_task: Option<JoinHandle<Result<()>>>,
 ) {
-    if let Some(http_task) = http_task {
-        http_task.abort();
-        let _ = http_task.await;
-    }
-    if let Some(admin_task) = admin_task {
-        admin_task.abort();
-        let _ = admin_task.await;
-    }
+    abort_task(http_task).await;
+    abort_task(socks_task).await;
+    abort_task(admin_task).await;
 }
 
 impl Drop for NetworkProxyHandle {
@@ -168,9 +201,10 @@ impl Drop for NetworkProxyHandle {
             return;
         }
         let http_task = self.http_task.take();
+        let socks_task = self.socks_task.take();
         let admin_task = self.admin_task.take();
         tokio::spawn(async move {
-            abort_tasks(http_task, admin_task).await;
+            abort_tasks(http_task, socks_task, admin_task).await;
         });
     }
 }