Add top-level exec-server subcommand (#17162)

## Summary
- add a top-level `codex exec-server` subcommand, marked experimental in
CLI help
- launch an adjacent or PATH-provided `codex-exec-server`, with a
source-tree `cargo run -p codex-exec-server --` fallback
- cover the new subcommand parser path

## Validation
- `just fmt`
- `git diff --check`
- not run: Rust test suite

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

---------

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

codex-rs/cli/Cargo.toml

@@ -30,6 +30,7 @@ codex-utils-cli = { workspace = true }
 codex-config = { workspace = true }
 codex-core = { workspace = true }
 codex-exec = { workspace = true }
+codex-exec-server = { workspace = true }
 codex-execpolicy = { workspace = true }
 codex-features = { workspace = true }
 codex-login = { workspace = true }

codex-rs/cli/src/main.rs

@@ -150,6 +150,9 @@ enum Subcommand {
     #[clap(hide = true, name = "stdio-to-uds")]
     StdioToUds(StdioToUdsCommand),
 
+    /// [EXPERIMENTAL] Run the standalone exec-server binary.
+    ExecServer(ExecServerCommand),
+
     /// Inspect feature flags.
     Features(FeaturesCli),
 }
@@ -376,6 +379,17 @@ struct AppServerCommand {
     auth: codex_app_server::AppServerWebsocketAuthArgs,
 }
 
+#[derive(Debug, Parser)]
+struct ExecServerCommand {
+    /// Transport endpoint URL. Supported values: `ws://IP:PORT` (default).
+    #[arg(
+        long = "listen",
+        value_name = "URL",
+        default_value = "ws://127.0.0.1:0"
+    )]
+    listen: String,
+}
+
 #[derive(Debug, clap::Subcommand)]
 #[allow(clippy::enum_variant_names)]
 enum AppServerSubcommand {
@@ -994,6 +1008,14 @@ async fn cli_main(arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
             tokio::task::spawn_blocking(move || codex_stdio_to_uds::run(socket_path.as_path()))
                 .await??;
         }
+        Some(Subcommand::ExecServer(cmd)) => {
+            reject_remote_mode_for_subcommand(
+                root_remote.as_deref(),
+                root_remote_auth_token_env.as_deref(),
+                "exec-server",
+            )?;
+            run_exec_server_command(cmd).await?;
+        }
         Some(Subcommand::Features(FeaturesCli { sub })) => match sub {
             FeaturesSubcommand::List => {
                 reject_remote_mode_for_subcommand(
@@ -1064,6 +1086,12 @@ 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)
+        .await
+        .map_err(anyhow::Error::from_boxed)
+}
+
 async fn enable_feature_in_config(interactive: &TuiCli, feature: &str) -> anyhow::Result<()> {
     FeatureToggles::validate_feature(feature)?;
     let codex_home = find_codex_home()?;