feat(sandbox): enforce proxy-aware network routing in sandbox (#11113)

## Summary
- expand proxy env injection to cover common tool env vars
(`HTTP_PROXY`/`HTTPS_PROXY`/`ALL_PROXY`/`NO_PROXY` families +
tool-specific variants)
- harden macOS Seatbelt network policy generation to route through
inferred loopback proxy endpoints and fail closed when proxy env is
malformed
- thread proxy-aware Linux sandbox flags and add minimal bwrap netns
isolation hook for restricted non-proxy runs
- add/refresh tests for proxy env wiring, Seatbelt policy generation,
and Linux sandbox argument wiring

codex-rs/core/src/spawn.rs

@@ -1,3 +1,4 @@
+use codex_network_proxy::NetworkProxy;
 use std::collections::HashMap;
 use std::path::PathBuf;
 use std::process::Stdio;
@@ -35,15 +36,29 @@ pub enum StdioPolicy {
 /// For now, we take `SandboxPolicy` as a parameter to spawn_child() because
 /// we need to determine whether to set the
 /// `CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR` environment variable.
-pub(crate) async fn spawn_child_async(
-    program: PathBuf,
-    args: Vec<String>,
-    #[cfg_attr(not(unix), allow(unused_variables))] arg0: Option<&str>,
-    cwd: PathBuf,
-    sandbox_policy: &SandboxPolicy,
-    stdio_policy: StdioPolicy,
-    env: HashMap<String, String>,
-) -> std::io::Result<Child> {
+pub(crate) struct SpawnChildRequest<'a> {
+    pub program: PathBuf,
+    pub args: Vec<String>,
+    pub arg0: Option<&'a str>,
+    pub cwd: PathBuf,
+    pub sandbox_policy: &'a SandboxPolicy,
+    pub network: Option<&'a NetworkProxy>,
+    pub stdio_policy: StdioPolicy,
+    pub env: HashMap<String, String>,
+}
+
+pub(crate) async fn spawn_child_async(request: SpawnChildRequest<'_>) -> std::io::Result<Child> {
+    let SpawnChildRequest {
+        program,
+        args,
+        arg0,
+        cwd,
+        sandbox_policy,
+        network,
+        stdio_policy,
+        mut env,
+    } = request;
+
     trace!(
         "spawn_child_async: {program:?} {args:?} {arg0:?} {cwd:?} {sandbox_policy:?} {stdio_policy:?} {env:?}"
     );
@@ -53,6 +68,9 @@ pub(crate) async fn spawn_child_async(
     cmd.arg0(arg0.map_or_else(|| program.to_string_lossy().to_string(), String::from));
     cmd.args(args);
     cmd.current_dir(cwd);
+    if let Some(network) = network {
+        network.apply_to_env(&mut env);
+    }
     cmd.env_clear();
     cmd.envs(env);