linux-sandbox: plumb split sandbox policies through helper (#13449)

## Why

The Linux sandbox helper still only accepted the legacy `SandboxPolicy`
payload.

That meant the runtime could compute split filesystem and network
policies, but the helper would immediately collapse them back to the
compatibility projection before applying seccomp or staging the
bubblewrap inner command.

## What changed

- added hidden `--file-system-sandbox-policy` and
`--network-sandbox-policy` flags alongside the legacy `--sandbox-policy`
flag so the helper can migrate incrementally
- updated the core-side Landlock wrapper to pass the split policies
explicitly when launching `codex-linux-sandbox`
- added helper-side resolution logic that accepts either the legacy
policy alone or a complete split-policy pair and normalizes that into
one effective configuration
- switched Linux helper network decisions to use `NetworkSandboxPolicy`
directly
- added `FromStr` support for the split policy types so the helper can
parse them from CLI JSON

## Verification

- added helper coverage in `linux-sandbox/src/linux_run_main_tests.rs`
for split-policy flags and policy resolution
- added CLI argument coverage in `core/src/landlock.rs`
- verified the current PR state with `just clippy`




---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/13449).
* #13453
* #13452
* #13451
* __->__ #13449
* #13448
* #13445
* #13440
* #13439

---------

Co-authored-by: viyatb-oai <viyatb@openai.com>

codex-rs/core/src/landlock.rs

@@ -3,6 +3,7 @@ use crate::spawn::SpawnChildRequest;
 use crate::spawn::StdioPolicy;
 use crate::spawn::spawn_child_async;
 use codex_network_proxy::NetworkProxy;
+use codex_protocol::permissions::FileSystemSandboxPolicy;
 use codex_protocol::permissions::NetworkSandboxPolicy;
 use std::collections::HashMap;
 use std::path::Path;
@@ -14,9 +15,9 @@ use tokio::process::Child;
 /// isolation plus seccomp for network restrictions.
 ///
 /// Unlike macOS Seatbelt where we directly embed the policy text, the Linux
-/// helper accepts a list of `--sandbox-permission`/`-s` flags mirroring the
-/// public CLI. We convert the internal [`SandboxPolicy`] representation into
-/// the equivalent CLI options.
+/// helper is a separate executable. We pass the legacy [`SandboxPolicy`] plus
+/// split filesystem/network policies as JSON so the helper can migrate
+/// incrementally without breaking older call sites.
 #[allow(clippy::too_many_arguments)]
 pub async fn spawn_command_under_linux_sandbox<P>(
     codex_linux_sandbox_exe: P,
@@ -32,9 +33,13 @@ pub async fn spawn_command_under_linux_sandbox<P>(
 where
     P: AsRef<Path>,
 {
-    let args = create_linux_sandbox_command_args(
+    let file_system_sandbox_policy = FileSystemSandboxPolicy::from(sandbox_policy);
+    let network_sandbox_policy = NetworkSandboxPolicy::from(sandbox_policy);
+    let args = create_linux_sandbox_command_args_for_policies(
         command,
         sandbox_policy,
+        &file_system_sandbox_policy,
+        network_sandbox_policy,
         sandbox_policy_cwd,
         use_bwrap_sandbox,
         allow_network_for_proxy(false),
@@ -45,7 +50,7 @@ where
         args,
         arg0,
         cwd: command_cwd,
-        network_sandbox_policy: NetworkSandboxPolicy::from(sandbox_policy),
+        network_sandbox_policy,
         network,
         stdio_policy,
         env,
@@ -60,32 +65,43 @@ pub(crate) fn allow_network_for_proxy(enforce_managed_network: bool) -> bool {
     enforce_managed_network
 }
 
-/// Converts the sandbox policy into the CLI invocation for `codex-linux-sandbox`.
+/// Converts the sandbox policies into the CLI invocation for
+/// `codex-linux-sandbox`.
 ///
 /// The helper performs the actual sandboxing (bubblewrap + seccomp) after
-/// parsing these arguments. See `docs/linux_sandbox.md` for the Linux semantics.
-pub(crate) fn create_linux_sandbox_command_args(
+/// parsing these arguments. Policy JSON flags are emitted before helper feature
+/// flags so the argv order matches the helper's CLI shape. See
+/// `docs/linux_sandbox.md` for the Linux semantics.
+#[allow(clippy::too_many_arguments)]
+pub(crate) fn create_linux_sandbox_command_args_for_policies(
     command: Vec<String>,
     sandbox_policy: &SandboxPolicy,
+    file_system_sandbox_policy: &FileSystemSandboxPolicy,
+    network_sandbox_policy: NetworkSandboxPolicy,
     sandbox_policy_cwd: &Path,
     use_bwrap_sandbox: bool,
     allow_network_for_proxy: bool,
 ) -> Vec<String> {
-    #[expect(clippy::expect_used)]
+    let sandbox_policy_json = serde_json::to_string(sandbox_policy)
+        .unwrap_or_else(|err| panic!("failed to serialize sandbox policy: {err}"));
+    let file_system_policy_json = serde_json::to_string(file_system_sandbox_policy)
+        .unwrap_or_else(|err| panic!("failed to serialize filesystem sandbox policy: {err}"));
+    let network_policy_json = serde_json::to_string(&network_sandbox_policy)
+        .unwrap_or_else(|err| panic!("failed to serialize network sandbox policy: {err}"));
     let sandbox_policy_cwd = sandbox_policy_cwd
         .to_str()
-        .expect("cwd must be valid UTF-8")
+        .unwrap_or_else(|| panic!("cwd must be valid UTF-8"))
         .to_string();
 
-    #[expect(clippy::expect_used)]
-    let sandbox_policy_json =
-        serde_json::to_string(sandbox_policy).expect("Failed to serialize SandboxPolicy to JSON");
-
     let mut linux_cmd: Vec<String> = vec![
         "--sandbox-policy-cwd".to_string(),
         sandbox_policy_cwd,
         "--sandbox-policy".to_string(),
         sandbox_policy_json,
+        "--file-system-sandbox-policy".to_string(),
+        file_system_policy_json,
+        "--network-sandbox-policy".to_string(),
+        network_policy_json,
     ];
     if use_bwrap_sandbox {
         linux_cmd.push("--use-bwrap-sandbox".to_string());
@@ -93,6 +109,32 @@ pub(crate) fn create_linux_sandbox_command_args(
     if allow_network_for_proxy {
         linux_cmd.push("--allow-network-for-proxy".to_string());
     }
+    linux_cmd.push("--".to_string());
+    linux_cmd.extend(command);
+    linux_cmd
+}
+
+/// Converts the sandbox cwd and execution options into the CLI invocation for
+/// `codex-linux-sandbox`.
+#[cfg(test)]
+pub(crate) fn create_linux_sandbox_command_args(
+    command: Vec<String>,
+    sandbox_policy_cwd: &Path,
+    use_bwrap_sandbox: bool,
+    allow_network_for_proxy: bool,
+) -> Vec<String> {
+    let sandbox_policy_cwd = sandbox_policy_cwd
+        .to_str()
+        .unwrap_or_else(|| panic!("cwd must be valid UTF-8"))
+        .to_string();
+
+    let mut linux_cmd: Vec<String> = vec!["--sandbox-policy-cwd".to_string(), sandbox_policy_cwd];
+    if use_bwrap_sandbox {
+        linux_cmd.push("--use-bwrap-sandbox".to_string());
+    }
+    if allow_network_for_proxy {
+        linux_cmd.push("--allow-network-for-proxy".to_string());
+    }
 
     // Separator so that command arguments starting with `-` are not parsed as
     // options of the helper itself.
@@ -113,16 +155,14 @@ mod tests {
     fn bwrap_flags_are_feature_gated() {
         let command = vec!["/bin/true".to_string()];
         let cwd = Path::new("/tmp");
-        let policy = SandboxPolicy::new_read_only_policy();
 
-        let with_bwrap =
-            create_linux_sandbox_command_args(command.clone(), &policy, cwd, true, false);
+        let with_bwrap = create_linux_sandbox_command_args(command.clone(), cwd, true, false);
         assert_eq!(
             with_bwrap.contains(&"--use-bwrap-sandbox".to_string()),
             true
         );
 
-        let without_bwrap = create_linux_sandbox_command_args(command, &policy, cwd, false, false);
+        let without_bwrap = create_linux_sandbox_command_args(command, cwd, false, false);
         assert_eq!(
             without_bwrap.contains(&"--use-bwrap-sandbox".to_string()),
             false
@@ -133,15 +173,46 @@ mod tests {
     fn proxy_flag_is_included_when_requested() {
         let command = vec!["/bin/true".to_string()];
         let cwd = Path::new("/tmp");
-        let policy = SandboxPolicy::new_read_only_policy();
 
-        let args = create_linux_sandbox_command_args(command, &policy, cwd, true, true);
+        let args = create_linux_sandbox_command_args(command, cwd, true, true);
         assert_eq!(
             args.contains(&"--allow-network-for-proxy".to_string()),
             true
         );
     }
 
+    #[test]
+    fn split_policy_flags_are_included() {
+        let command = vec!["/bin/true".to_string()];
+        let cwd = Path::new("/tmp");
+        let sandbox_policy = SandboxPolicy::new_read_only_policy();
+        let file_system_sandbox_policy = FileSystemSandboxPolicy::from(&sandbox_policy);
+        let network_sandbox_policy = NetworkSandboxPolicy::from(&sandbox_policy);
+
+        let args = create_linux_sandbox_command_args_for_policies(
+            command,
+            &sandbox_policy,
+            &file_system_sandbox_policy,
+            network_sandbox_policy,
+            cwd,
+            true,
+            false,
+        );
+
+        assert_eq!(
+            args.windows(2).any(|window| {
+                window[0] == "--file-system-sandbox-policy" && !window[1].is_empty()
+            }),
+            true
+        );
+        assert_eq!(
+            args.windows(2)
+                .any(|window| window[0] == "--network-sandbox-policy"
+                    && window[1] == "\"restricted\""),
+            true
+        );
+    }
+
     #[test]
     fn proxy_network_requires_managed_requirements() {
         assert_eq!(allow_network_for_proxy(false), false);

codex-rs/core/src/sandboxing/mod.rs

@@ -14,7 +14,7 @@ use crate::exec::SandboxType;
 use crate::exec::StdoutStream;
 use crate::exec::execute_exec_request;
 use crate::landlock::allow_network_for_proxy;
-use crate::landlock::create_linux_sandbox_command_args;
+use crate::landlock::create_linux_sandbox_command_args_for_policies;
 use crate::protocol::SandboxPolicy;
 #[cfg(target_os = "macos")]
 use crate::seatbelt::MACOS_PATH_TO_SEATBELT_EXECUTABLE;
@@ -516,9 +516,11 @@ impl SandboxManager {
                 let exe = codex_linux_sandbox_exe
                     .ok_or(SandboxTransformError::MissingLinuxSandboxExecutable)?;
                 let allow_proxy_network = allow_network_for_proxy(enforce_managed_network);
-                let mut args = create_linux_sandbox_command_args(
+                let mut args = create_linux_sandbox_command_args_for_policies(
                     command.clone(),
                     &effective_policy,
+                    &effective_file_system_policy,
+                    effective_network_policy,
                     sandbox_policy_cwd,
                     use_linux_sandbox_bwrap,
                     allow_proxy_network,