Add executor-local config reads to the exec server (#37408)

## What changed

- Add the `environmentConfig/read` RPC for selecting literal TOML paths from executor-local config and requirements layers.
- Return layer precedence, cloud insertion points, source and base-directory metadata, and executor home and hostname context without normalizing path-bearing values.
- Expose the operation through both remote clients and local `Environment` instances, with invalid selectors reported as invalid parameters.

## Testing

- Cover projected remote config reads and rejection of empty selectors.

GitOrigin-RevId: fee15bf833de6bcb2058d405ed5b1d5d928d7218

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

@@ -16,8 +16,12 @@ use crate::ExecServerRuntimePaths;
 use crate::client::http_client::PendingRouteAwareHttpBodyStream;
 use crate::client::http_client::RouteAwareHttpClient;
 use crate::client::http_client::RouteAwareHttpRequestRunner;
+use crate::environment_config::ReadEnvironmentConfigError;
+use crate::environment_config::read_environment_config;
 use crate::protocol::CapabilityRootsDiscoverParams;
 use crate::protocol::CapabilityRootsDiscoverResponse;
+use crate::protocol::EnvironmentConfigReadParams;
+use crate::protocol::EnvironmentConfigReadResponse;
 use crate::protocol::EnvironmentInfo;
 use crate::protocol::EnvironmentStatus;
 use crate::protocol::EnvironmentStatusKind;
@@ -175,6 +179,19 @@ impl ExecServerHandler {
         Ok(EnvironmentInfo::local())
     }
 
+    pub(crate) async fn environment_config_read(
+        &self,
+        params: EnvironmentConfigReadParams,
+    ) -> Result<EnvironmentConfigReadResponse, JSONRPCErrorError> {
+        self.require_initialized_for("environment config")?;
+        read_environment_config(crate::LOCAL_FS.as_ref(), params)
+            .await
+            .map_err(|error| match error {
+                ReadEnvironmentConfigError::InvalidParams(message) => invalid_params(message),
+                ReadEnvironmentConfigError::Internal(message) => internal_error(message),
+            })
+    }
+
     pub(crate) fn environment_status(&self) -> Result<EnvironmentStatus, JSONRPCErrorError> {
         self.require_initialized_for("environment status")?;
         Ok(EnvironmentStatus {

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

@@ -2,6 +2,7 @@ use std::sync::Arc;
 
 use crate::protocol::CAPABILITY_ROOTS_DISCOVER_METHOD;
 use crate::protocol::CapabilityRootsDiscoverParams;
+use crate::protocol::ENVIRONMENT_CONFIG_READ_METHOD;
 use crate::protocol::ENVIRONMENT_INFO_METHOD;
 use crate::protocol::ENVIRONMENT_STATUS_METHOD;
 use crate::protocol::EXEC_METHOD;
@@ -9,6 +10,7 @@ use crate::protocol::EXEC_READ_METHOD;
 use crate::protocol::EXEC_SIGNAL_METHOD;
 use crate::protocol::EXEC_TERMINATE_METHOD;
 use crate::protocol::EXEC_WRITE_METHOD;
+use crate::protocol::EnvironmentConfigReadParams;
 use crate::protocol::ExecParams;
 use crate::protocol::FS_CANONICALIZE_METHOD;
 use crate::protocol::FS_CLOSE_METHOD;
@@ -74,6 +76,12 @@ pub(crate) fn build_router() -> RpcRouter<ExecServerHandler> {
         ENVIRONMENT_INFO_METHOD,
         |handler: Arc<ExecServerHandler>, _params: ()| async move { handler.environment_info() },
     );
+    router.request(
+        ENVIRONMENT_CONFIG_READ_METHOD,
+        |handler: Arc<ExecServerHandler>, params: EnvironmentConfigReadParams| async move {
+            handler.environment_config_read(params).await
+        },
+    );
     router.request(
         ENVIRONMENT_STATUS_METHOD,
         |handler: Arc<ExecServerHandler>, _params: ()| async move { handler.environment_status() },