Add cloud executor registration to exec-server

codex-rs/exec-server/README.md

@@ -22,6 +22,12 @@ the wire.
 The CLI entrypoint supports:
 
 - `ws://IP:PORT` (default)
+- `--cloud --cloud-base-url URL [--cloud-environment-id ID] [--cloud-name NAME]`
+
+Cloud mode registers the local exec-server with the cloud environments service,
+then reconnects to the service-provided rendezvous websocket as the executor.
+It requires ChatGPT auth, and `CODEX_CLOUD_ENVIRONMENTS_BASE_URL` can be used
+instead of `--cloud-base-url`.
 
 Wire framing:
 
@@ -308,6 +314,8 @@ The crate exports:
 - `DEFAULT_LISTEN_URL` and `ExecServerListenUrlParseError`
 - `ExecServerRuntimePaths`
 - `run_main()` for embedding the websocket server
+- `CloudExecutorConfig` and `run_cloud_executor()` for embedding cloud
+  registration mode
 
 Callers must pass `ExecServerRuntimePaths` to `run_main()`. The top-level
 `codex exec-server` command builds these paths from the `codex` arg0 dispatch