[codex] Report the exec-server working directory (#29666)

## Summary

- add the exec-server working directory to `environment/info` as an
optional `PathUri`
- populate it from the executor process's current directory
- preserve compatibility with older responses that omit `cwd`

## Why

Remote clients currently have no executor-native default working
directory. This forces callers such as app-server-backend to assume
`/workspace`, which fails for laptop environments. Reporting the cwd
alongside the detected shell lets clients use the path convention and
location of the actual executor.

## Impact

This is backward-compatible: the new response field is optional, and
clients can continue handling responses from older exec servers. A
follow-up app-server-backend change will consume the value for cwd-less
`command/exec` requests.

## Validation

- `just test -p codex-exec-server` (275 passed, 2 skipped)

codex-rs/exec-server/src/environment.rs

@@ -28,6 +28,7 @@ use crate::remote::NoiseRendezvousEnvironmentConfig;
 use crate::remote_file_system::RemoteFileSystem;
 use crate::remote_process::RemoteProcess;
 use codex_shell_command::shell_detect::DetectedShell;
+use codex_utils_path_uri::PathUri;
 use tokio_util::task::AbortOnDropHandle;
 
 pub const CODEX_EXEC_SERVER_URL_ENV_VAR: &str = "CODEX_EXEC_SERVER_URL";
@@ -608,6 +609,9 @@ impl EnvironmentInfo {
     pub(crate) fn local() -> Self {
         Self {
             shell: codex_shell_command::shell_detect::default_user_shell().into(),
+            cwd: std::env::current_dir()
+                .ok()
+                .and_then(|cwd| PathUri::from_host_native_path(cwd).ok()),
         }
     }
 }
@@ -655,6 +659,19 @@ mod tests {
         assert!(manager.try_local_environment().is_none());
     }
 
+    #[test]
+    fn local_environment_info_includes_current_directory() {
+        let info = super::EnvironmentInfo::local();
+
+        assert_eq!(
+            info.cwd,
+            Some(
+                PathUri::from_host_native_path(std::env::current_dir().expect("current directory"))
+                    .expect("cwd URI")
+            )
+        );
+    }
+
     #[tokio::test]
     async fn noise_environment_config_selects_remote_as_default() {
         let config = noise_environment_config_from_values(

codex-rs/exec-server/src/protocol.rs

@@ -72,6 +72,9 @@ pub struct InitializeResponse {
 #[serde(rename_all = "camelCase")]
 pub struct EnvironmentInfo {
     pub shell: ShellInfo,
+    /// Working directory inherited by the exec-server process.
+    #[serde(default)]
+    pub cwd: Option<PathUri>,
 }
 
 /// Shell detected for an execution/filesystem environment.
@@ -511,10 +514,12 @@ mod base64_bytes {
 
 #[cfg(test)]
 mod tests {
+    use super::EnvironmentInfo;
     use super::ExecParams;
     use super::FsReadFileParams;
     use super::HttpRequestParams;
     use super::ProcessId;
+    use super::ShellInfo;
     use codex_file_system::FileSystemSandboxContext;
     use codex_network_proxy::ManagedNetworkSandboxContext;
     use codex_protocol::models::PermissionProfile;
@@ -566,6 +571,25 @@ mod tests {
         assert_eq!(legacy.managed_network, None);
     }
 
+    #[test]
+    fn environment_info_accepts_legacy_response_without_cwd() {
+        let info: EnvironmentInfo = serde_json::from_value(serde_json::json!({
+            "shell": { "name": "zsh", "path": "/bin/zsh" }
+        }))
+        .expect("legacy environment info should deserialize");
+
+        assert_eq!(
+            info,
+            EnvironmentInfo {
+                shell: ShellInfo {
+                    name: "zsh".to_string(),
+                    path: "/bin/zsh".to_string(),
+                },
+                cwd: None,
+            }
+        );
+    }
+
     #[test]
     fn filesystem_protocol_accepts_legacy_absolute_paths_and_serializes_path_uris() {
         let legacy_path = std::env::current_dir()