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-protocol/src/environment_config.rs

@@ -0,0 +1,50 @@
+use codex_utils_path_uri::PathUri;
+use serde::Deserialize;
+use serde::Serialize;
+
+pub const ENVIRONMENT_CONFIG_READ_METHOD: &str = "environmentConfig/read";
+
+/// Selects executor-local config and requirements fields by literal TOML key path.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct EnvironmentConfigReadParams {
+    pub cwd: PathUri,
+    pub config_paths: Vec<Vec<String>>,
+    pub requirements_paths: Vec<Vec<String>>,
+}
+
+/// Executor-local config and requirements layers selected for one environment.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct EnvironmentConfigReadResponse {
+    /// Executor user home used to expand `~` in path-bearing values.
+    pub user_home_dir: Option<PathUri>,
+    /// Executor Codex home used as the base directory for cloud-provided layers.
+    pub codex_home_dir: PathUri,
+    /// Executor hostname used to select matching remote sandbox requirements.
+    pub hostname: Option<String>,
+    pub config: EnvironmentConfigLayerStack,
+    pub requirements: EnvironmentConfigLayerStack,
+}
+
+/// One ordered set of selected TOML layers.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct EnvironmentConfigLayerStack {
+    /// Layers ordered from lowest to highest precedence.
+    pub layers: Vec<EnvironmentConfigLayer>,
+    /// Position at which cloud-provided layers should be inserted.
+    pub cloud_insertion_index: usize,
+}
+
+/// One selected executor-local TOML layer.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct EnvironmentConfigLayer {
+    /// Opaque provenance for diagnostics. Callers must not derive behavior from it.
+    pub source: String,
+    /// Directory used to interpret relative paths in this layer.
+    pub base_dir: PathUri,
+    /// Selected raw TOML. Path-bearing values have not been normalized.
+    pub toml: String,
+}

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

@@ -1,8 +1,10 @@
+mod environment_config;
 mod network_policy;
 mod process_id;
 mod protocol;
 pub mod rpc;
 
+pub use environment_config::*;
 pub use network_policy::*;
 pub use process_id::ProcessId;
 pub use protocol::*;