feat: load defaults into Config and introduce ConfigOverrides

codex-rs/core/src/approval_mode_cli_arg.rs

@@ -6,7 +6,7 @@ use clap::ValueEnum;
 use crate::protocol::AskForApproval;
 use crate::protocol::SandboxPolicy;
 
-#[derive(Clone, Debug, ValueEnum)]
+#[derive(Clone, Copy, Debug, ValueEnum)]
 #[value(rename_all = "kebab-case")]
 pub enum ApprovalModeCliArg {
     /// Run all commands without asking for user approval.
@@ -24,7 +24,7 @@ pub enum ApprovalModeCliArg {
     Never,
 }
 
-#[derive(Clone, Debug, ValueEnum)]
+#[derive(Clone, Copy, Debug, ValueEnum)]
 #[value(rename_all = "kebab-case")]
 pub enum SandboxModeCliArg {
     /// Network syscalls will be blocked

codex-rs/core/src/codex.rs

@@ -36,7 +36,6 @@ use crate::exec::process_exec_tool_call;
 use crate::exec::ExecParams;
 use crate::exec::ExecToolCallOutput;
 use crate::exec::SandboxType;
-use crate::flags::OPENAI_DEFAULT_MODEL;
 use crate::flags::OPENAI_STREAM_MAX_RETRIES;
 use crate::models::ContentItem;
 use crate::models::FunctionCallOutputPayload;
@@ -486,7 +485,6 @@ async fn submission_loop(
                 sandbox_policy,
                 disable_response_storage,
             } => {
-                let model = model.unwrap_or_else(|| OPENAI_DEFAULT_MODEL.to_string());
                 info!(model, "Configuring session");
                 let client = ModelClient::new(model.clone());
 

codex-rs/core/src/codex_wrapper.rs

@@ -2,16 +2,13 @@ use std::sync::atomic::AtomicU64;
 use std::sync::Arc;
 
 use crate::config::Config;
-use crate::protocol::AskForApproval;
 use crate::protocol::Event;
 use crate::protocol::EventMsg;
 use crate::protocol::Op;
-use crate::protocol::SandboxPolicy;
 use crate::protocol::Submission;
 use crate::util::notify_on_sigint;
 use crate::Codex;
 use tokio::sync::Notify;
-use tracing::debug;
 
 /// Spawn a new [`Codex`] and initialise the session.
 ///
@@ -19,21 +16,17 @@ use tracing::debug;
 /// is received as a response to the initial `ConfigureSession` submission so
 /// that callers can surface the information to the UI.
 pub async fn init_codex(
-    approval_policy: AskForApproval,
-    sandbox_policy: SandboxPolicy,
+    config: Config,
     disable_response_storage: bool,
-    model_override: Option<String>,
 ) -> anyhow::Result<(CodexWrapper, Event, Arc<Notify>)> {
     let ctrl_c = notify_on_sigint();
-    let config = Config::load().unwrap_or_default();
-    debug!("loaded config: {config:?}");
     let codex = CodexWrapper::new(Codex::spawn(ctrl_c.clone())?);
     let init_id = codex
         .submit(Op::ConfigureSession {
-            model: model_override.or_else(|| config.model.clone()),
-            instructions: config.instructions,
-            approval_policy,
-            sandbox_policy,
+            model: config.model.clone(),
+            instructions: config.instructions.clone(),
+            approval_policy: config.approval_policy,
+            sandbox_policy: config.sandbox_policy,
             disable_response_storage,
         })
         .await?;

codex-rs/core/src/config.rs

@@ -1,39 +1,89 @@
-use std::path::PathBuf;
-
+use crate::flags::OPENAI_DEFAULT_MODEL;
+use crate::protocol::AskForApproval;
+use crate::protocol::SandboxPolicy;
 use dirs::home_dir;
 use serde::Deserialize;
+use std::path::PathBuf;
 
-/// Embedded fallback instructions that mirror the TypeScript CLI’s default system prompt. These
-/// are compiled into the binary so a clean install behaves correctly even if the user has not
-/// created `~/.codex/instructions.md`.
+/// Embedded fallback instructions that mirror the TypeScript CLI’s default
+/// system prompt. These are compiled into the binary so a clean install behaves
+/// correctly even if the user has not created `~/.codex/instructions.md`.
 const EMBEDDED_INSTRUCTIONS: &str = include_str!("../prompt.md");
 
-#[derive(Default, Deserialize, Debug, Clone)]
+/// Application configuration loaded from disk and merged with overrides.
+#[derive(Deserialize, Debug, Clone)]
 pub struct Config {
-    pub model: Option<String>,
+    /// Optional override of model selection.
+    #[serde(default = "default_model")]
+    pub model: String,
+    /// Default approval policy for executing commands.
+    #[serde(default)]
+    pub approval_policy: AskForApproval,
+    #[serde(default)]
+    pub sandbox_policy: SandboxPolicy,
+    /// System instructions.
     pub instructions: Option<String>,
 }
 
+/// Optional overrides for user configuration (e.g., from CLI flags).
+#[derive(Default, Debug, Clone)]
+pub struct ConfigOverrides {
+    pub model: Option<String>,
+    pub approval_policy: Option<AskForApproval>,
+    pub sandbox_policy: Option<SandboxPolicy>,
+}
+
 impl Config {
-    /// Load ~/.codex/config.toml and ~/.codex/instructions.md (if present).
-    /// Returns `None` if neither file exists.
-    pub fn load() -> Option<Self> {
-        let mut cfg: Config = Self::load_from_toml().unwrap_or_default();
-
-        // Highest precedence → user‑provided ~/.codex/instructions.md (if present)
-        // Fallback           → embedded default instructions baked into the binary
+    /// Load configuration, optionally applying overrides (CLI flags). Merges
+    /// ~/.codex/config.toml, ~/.codex/instructions.md, embedded defaults, and
+    /// any values provided in `overrides` (highest precedence).
+    pub fn load_with_overrides(overrides: ConfigOverrides) -> std::io::Result<Self> {
+        let mut cfg: Config = Self::load_from_toml()?;
+        tracing::warn!("cfg: {cfg:?}");
 
+        // Instructions: user-provided instructions.md > embedded default.
         cfg.instructions =
             Self::load_instructions().or_else(|| Some(EMBEDDED_INSTRUCTIONS.to_string()));
 
-        Some(cfg)
+        // Apply overrides.
+        if let Some(model) = overrides.model {
+            cfg.model = model;
+        }
+        if let Some(policy) = overrides.approval_policy {
+            cfg.approval_policy = policy;
+        }
+        if let Some(policy) = overrides.sandbox_policy {
+            cfg.sandbox_policy = policy;
+        }
+        Ok(cfg)
     }
 
-    fn load_from_toml() -> Option<Self> {
-        let mut p = codex_dir().ok()?;
-        p.push("config.toml");
-        let contents = std::fs::read_to_string(&p).ok()?;
-        toml::from_str(&contents).ok()
+    fn load_from_toml() -> std::io::Result<Self> {
+        let config_toml_path = codex_dir()?.join("config.toml");
+        match std::fs::read_to_string(&config_toml_path) {
+            Ok(contents) => toml::from_str::<Self>(&contents).map_err(|e| {
+                tracing::error!("Failed to parse config.toml: {e}");
+                std::io::Error::new(std::io::ErrorKind::InvalidData, e)
+            }),
+            Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+                tracing::info!("config.toml not found, using defaults");
+                Ok(Self::load_default_config())
+            }
+            Err(e) => {
+                tracing::error!("Failed to read config.toml: {e}");
+                Err(e)
+            }
+        }
+    }
+
+    pub fn load_default_config_for_test() -> Self {
+        Self::load_default_config()
+    }
+
+    fn load_default_config() -> Self {
+        // Load from an empty string to exercise #[serde(default)] to
+        // get the default values for each field.
+        toml::from_str::<Self>("").expect("empty string should parse as TOML")
     }
 
     fn load_instructions() -> Option<String> {
@@ -43,6 +93,11 @@ impl Config {
     }
 }
 
+fn default_model() -> String {
+    tracing::warn!("OPENAI_DEFAULT_MODEL: {OPENAI_DEFAULT_MODEL}");
+    OPENAI_DEFAULT_MODEL.to_string()
+}
+
 /// Returns the path to the Codex configuration directory, which is `~/.codex`.
 /// Does not verify that the directory exists.
 pub fn codex_dir() -> std::io::Result<PathBuf> {

codex-rs/core/src/exec.rs

@@ -98,7 +98,7 @@ pub async fn process_exec_tool_call(
                 workdir,
                 timeout_ms,
             } = params;
-            let seatbelt_command = create_seatbelt_command(command, writable_roots);
+            let seatbelt_command = create_seatbelt_command(command, sandbox_policy, writable_roots);
             exec(
                 ExecParams {
                     command: seatbelt_command,
@@ -154,7 +154,11 @@ pub async fn process_exec_tool_call(
     }
 }
 
-pub fn create_seatbelt_command(command: Vec<String>, writable_roots: &[PathBuf]) -> Vec<String> {
+pub fn create_seatbelt_command(
+    command: Vec<String>,
+    sandbox_policy: SandboxPolicy,
+    writable_roots: &[PathBuf],
+) -> Vec<String> {
     let (policies, cli_args): (Vec<String>, Vec<String>) = writable_roots
         .iter()
         .enumerate()
@@ -166,6 +170,13 @@ pub fn create_seatbelt_command(command: Vec<String>, writable_roots: &[PathBuf])
         })
         .unzip();
 
+    // TODO(ragona): The seatbelt policy should reflect the SandboxPolicy that
+    // is passed, but everything is currently hardcoded to use
+    // MACOS_SEATBELT_READONLY_POLICY.
+    if !matches!(sandbox_policy, SandboxPolicy::NetworkRestricted) {
+        tracing::error!("specified sandbox policy {sandbox_policy:?} will not be honroed");
+    }
+
     let full_policy = if policies.is_empty() {
         MACOS_SEATBELT_READONLY_POLICY.to_string()
     } else {

codex-rs/core/src/protocol.rs

@@ -26,7 +26,7 @@ pub enum Op {
     /// Configure the model session.
     ConfigureSession {
         /// If not specified, server will use its default model.
-        model: Option<String>,
+        model: String,
         /// Model instructions
         instructions: Option<String>,
         /// When to escalate for approval for execution
@@ -66,11 +66,13 @@ pub enum Op {
 }
 
 /// Determines how liberally commands are auto‑approved by the system.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
 pub enum AskForApproval {
     /// Under this policy, only “known safe” commands—as determined by
     /// `is_safe_command()`—that **only read files** are auto‑approved.
     /// Everything else will ask the user to approve.
+    #[default]
     UnlessAllowListed,
 
     /// In addition to everything allowed by **`Suggest`**, commands that
@@ -91,13 +93,15 @@ pub enum AskForApproval {
 }
 
 /// Determines execution restrictions for model shell commands
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
 pub enum SandboxPolicy {
     /// Network syscalls will be blocked
     NetworkRestricted,
     /// Filesystem writes will be restricted
     FileWriteRestricted,
     /// Network and filesystem writes will be restricted
+    #[default]
     NetworkAndFileWriteRestricted,
     /// No restrictions; full "unsandboxed" mode
     DangerousNoRestrictions,

codex-rs/core/tests/live_agent.rs

@@ -17,7 +17,7 @@
 
 use std::time::Duration;
 
-use codex_core::protocol::AskForApproval;
+use codex_core::config::Config;
 use codex_core::protocol::EventMsg;
 use codex_core::protocol::InputItem;
 use codex_core::protocol::Op;
@@ -47,13 +47,14 @@ async fn spawn_codex() -> Codex {
 
     let agent = Codex::spawn(std::sync::Arc::new(Notify::new())).unwrap();
 
+    let config = Config::load_default_config_for_test();
     agent
         .submit(Submission {
             id: "init".into(),
             op: Op::ConfigureSession {
-                model: None,
+                model: config.model,
                 instructions: None,
-                approval_policy: AskForApproval::OnFailure,
+                approval_policy: config.approval_policy,
                 sandbox_policy: SandboxPolicy::NetworkAndFileWriteRestricted,
                 disable_response_storage: false,
             },

codex-rs/core/tests/previous_response_id.rs

@@ -1,6 +1,6 @@
 use std::time::Duration;
 
-use codex_core::protocol::AskForApproval;
+use codex_core::config::Config;
 use codex_core::protocol::InputItem;
 use codex_core::protocol::Op;
 use codex_core::protocol::SandboxPolicy;
@@ -87,13 +87,14 @@ async fn keeps_previous_response_id_between_tasks() {
     let codex = Codex::spawn(std::sync::Arc::new(tokio::sync::Notify::new())).unwrap();
 
     // Init session
+    let config = Config::load_default_config_for_test();
     codex
         .submit(Submission {
             id: "init".into(),
             op: Op::ConfigureSession {
-                model: None,
+                model: config.model,
                 instructions: None,
-                approval_policy: AskForApproval::OnFailure,
+                approval_policy: config.approval_policy,
                 sandbox_policy: SandboxPolicy::NetworkAndFileWriteRestricted,
                 disable_response_storage: false,
             },

codex-rs/core/tests/stream_no_completed.rs

@@ -3,7 +3,7 @@
 
 use std::time::Duration;
 
-use codex_core::protocol::AskForApproval;
+use codex_core::config::Config;
 use codex_core::protocol::InputItem;
 use codex_core::protocol::Op;
 use codex_core::protocol::SandboxPolicy;
@@ -70,13 +70,14 @@ async fn retries_on_early_close() {
 
     let codex = Codex::spawn(std::sync::Arc::new(tokio::sync::Notify::new())).unwrap();
 
+    let config = Config::load_default_config_for_test();
     codex
         .submit(Submission {
             id: "init".into(),
             op: Op::ConfigureSession {
-                model: None,
+                model: config.model,
                 instructions: None,
-                approval_policy: AskForApproval::OnFailure,
+                approval_policy: config.approval_policy,
                 sandbox_policy: SandboxPolicy::NetworkAndFileWriteRestricted,
                 disable_response_storage: false,
             },