Run exec-server fs operations through sandbox helper (#17294)

## Summary
- run exec-server filesystem RPCs requiring sandboxing through a
`codex-fs` arg0 helper over stdin/stdout
- keep direct local filesystem execution for `DangerFullAccess` and
external sandbox policies
- remove the standalone exec-server binary path in favor of top-level
arg0 dispatch/runtime paths
- add sandbox escape regression coverage for local and remote filesystem
paths

## Validation
- `just fmt`
- `git diff --check`
- remote devbox: `cd codex-rs && bazel test --bes_backend=
--bes_results_url= //codex-rs/exec-server:all` (6/6 passed)

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/cli/src/main.rs

@@ -155,7 +155,7 @@ enum Subcommand {
     #[clap(hide = true, name = "stdio-to-uds")]
     StdioToUds(StdioToUdsCommand),
 
-    /// [EXPERIMENTAL] Run the standalone exec-server binary.
+    /// [EXPERIMENTAL] Run the standalone exec-server service.
     ExecServer(ExecServerCommand),
 
     /// Inspect feature flags.
@@ -1031,7 +1031,7 @@ async fn cli_main(arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
                 root_remote_auth_token_env.as_deref(),
                 "exec-server",
             )?;
-            run_exec_server_command(cmd).await?;
+            run_exec_server_command(cmd, &arg0_paths).await?;
         }
         Some(Subcommand::Features(FeaturesCli { sub })) => match sub {
             FeaturesSubcommand::List => {
@@ -1103,8 +1103,19 @@ async fn cli_main(arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
     Ok(())
 }
 
-async fn run_exec_server_command(cmd: ExecServerCommand) -> anyhow::Result<()> {
-    codex_exec_server::run_main_with_listen_url(&cmd.listen)
+async fn run_exec_server_command(
+    cmd: ExecServerCommand,
+    arg0_paths: &Arg0DispatchPaths,
+) -> anyhow::Result<()> {
+    let codex_self_exe = arg0_paths
+        .codex_self_exe
+        .clone()
+        .ok_or_else(|| anyhow::anyhow!("Codex executable path is not configured"))?;
+    let runtime_paths = codex_exec_server::ExecServerRuntimePaths::new(
+        codex_self_exe,
+        arg0_paths.codex_linux_sandbox_exe.clone(),
+    )?;
+    codex_exec_server::run_main(&cmd.listen, runtime_paths)
         .await
         .map_err(anyhow::Error::from_boxed)
 }