feat: feature flag (#4948)

Add proper feature flag instead of having custom flags for everything.
This is just for experimental/wip part of the code
It can be used through CLI:
```bash
codex --enable unified_exec --disable view_image_tool
```

Or in the `config.toml`
```toml
# Global toggles applied to every profile unless overridden.
[features]
apply_patch_freeform = true
view_image_tool = false
```

Follow-up:
In a following PR, the goal is to have a default have `bundles` of
features that we can associate to a model

codex-rs/cli/src/main.rs

@@ -26,6 +26,8 @@ use supports_color::Stream;
 mod mcp_cmd;
 
 use crate::mcp_cmd::McpCli;
+use codex_core::config::Config;
+use codex_core::config::ConfigOverrides;
 
 /// Codex CLI
 ///
@@ -45,6 +47,9 @@ struct MultitoolCli {
     #[clap(flatten)]
     pub config_overrides: CliConfigOverrides,
 
+    #[clap(flatten)]
+    pub feature_toggles: FeatureToggles,
+
     #[clap(flatten)]
     interactive: TuiCli,
 
@@ -97,6 +102,9 @@ enum Subcommand {
     /// Internal: run the responses API proxy.
     #[clap(hide = true)]
     ResponsesApiProxy(ResponsesApiProxyArgs),
+
+    /// Inspect feature flags.
+    Features(FeaturesCli),
 }
 
 #[derive(Debug, Parser)]
@@ -231,6 +239,53 @@ fn print_exit_messages(exit_info: AppExitInfo) {
     }
 }
 
+#[derive(Debug, Default, Parser, Clone)]
+struct FeatureToggles {
+    /// Enable a feature (repeatable). Equivalent to `-c features.<name>=true`.
+    #[arg(long = "enable", value_name = "FEATURE", action = clap::ArgAction::Append, global = true)]
+    enable: Vec<String>,
+
+    /// Disable a feature (repeatable). Equivalent to `-c features.<name>=false`.
+    #[arg(long = "disable", value_name = "FEATURE", action = clap::ArgAction::Append, global = true)]
+    disable: Vec<String>,
+}
+
+impl FeatureToggles {
+    fn to_overrides(&self) -> Vec<String> {
+        let mut v = Vec::new();
+        for k in &self.enable {
+            v.push(format!("features.{k}=true"));
+        }
+        for k in &self.disable {
+            v.push(format!("features.{k}=false"));
+        }
+        v
+    }
+}
+
+#[derive(Debug, Parser)]
+struct FeaturesCli {
+    #[command(subcommand)]
+    sub: FeaturesSubcommand,
+}
+
+#[derive(Debug, Parser)]
+enum FeaturesSubcommand {
+    /// List known features with their stage and effective state.
+    List,
+}
+
+fn stage_str(stage: codex_core::features::Stage) -> &'static str {
+    use codex_core::features::Stage;
+    match stage {
+        Stage::Experimental => "experimental",
+        Stage::Beta => "beta",
+        Stage::Stable => "stable",
+        Stage::Deprecated => "deprecated",
+        Stage::Removed => "removed",
+    }
+}
+
 /// As early as possible in the process lifecycle, apply hardening measures. We
 /// skip this in debug builds to avoid interfering with debugging.
 #[ctor::ctor]
@@ -248,11 +303,17 @@ fn main() -> anyhow::Result<()> {
 
 async fn cli_main(codex_linux_sandbox_exe: Option<PathBuf>) -> anyhow::Result<()> {
     let MultitoolCli {
-        config_overrides: root_config_overrides,
+        config_overrides: mut root_config_overrides,
+        feature_toggles,
         mut interactive,
         subcommand,
     } = MultitoolCli::parse();
 
+    // Fold --enable/--disable into config overrides so they flow to all subcommands.
+    root_config_overrides
+        .raw_overrides
+        .extend(feature_toggles.to_overrides());
+
     match subcommand {
         None => {
             prepend_config_flags(
@@ -381,6 +442,30 @@ async fn cli_main(codex_linux_sandbox_exe: Option<PathBuf>) -> anyhow::Result<()
         Some(Subcommand::GenerateTs(gen_cli)) => {
             codex_protocol_ts::generate_ts(&gen_cli.out_dir, gen_cli.prettier.as_deref())?;
         }
+        Some(Subcommand::Features(FeaturesCli { sub })) => match sub {
+            FeaturesSubcommand::List => {
+                // Respect root-level `-c` overrides plus top-level flags like `--profile`.
+                let cli_kv_overrides = root_config_overrides
+                    .parse_overrides()
+                    .map_err(|e| anyhow::anyhow!(e))?;
+
+                // Thread through relevant top-level flags (at minimum, `--profile`).
+                // Also honor `--search` since it maps to a feature toggle.
+                let overrides = ConfigOverrides {
+                    config_profile: interactive.config_profile.clone(),
+                    tools_web_search_request: interactive.web_search.then_some(true),
+                    ..Default::default()
+                };
+
+                let config = Config::load_with_cli_overrides(cli_kv_overrides, overrides).await?;
+                for def in codex_core::features::FEATURES.iter() {
+                    let name = def.key;
+                    let stage = stage_str(def.stage);
+                    let enabled = config.features.enabled(def.id);
+                    println!("{name}\t{stage}\t{enabled}");
+                }
+            }
+        },
     }
 
     Ok(())
@@ -484,6 +569,7 @@ mod tests {
             interactive,
             config_overrides: root_overrides,
             subcommand,
+            feature_toggles: _,
         } = cli;
 
         let Subcommand::Resume(ResumeCommand {

codex-rs/cli/src/mcp_cmd.rs

@@ -13,6 +13,7 @@ use codex_core::config::load_global_mcp_servers;
 use codex_core::config::write_global_mcp_servers;
 use codex_core::config_types::McpServerConfig;
 use codex_core::config_types::McpServerTransportConfig;
+use codex_core::features::Feature;
 use codex_core::mcp::auth::compute_auth_statuses;
 use codex_core::protocol::McpAuthStatus;
 use codex_rmcp_client::delete_oauth_tokens;
@@ -285,7 +286,7 @@ async fn run_login(config_overrides: &CliConfigOverrides, login_args: LoginArgs)
         .await
         .context("failed to load configuration")?;
 
-    if !config.use_experimental_use_rmcp_client {
+    if !config.features.enabled(Feature::RmcpClient) {
         bail!(
             "OAuth login is only supported when experimental_use_rmcp_client is true in config.toml."
         );