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/core/src/config.rs

@@ -17,6 +17,10 @@ use crate::config_types::ShellEnvironmentPolicy;
 use crate::config_types::ShellEnvironmentPolicyToml;
 use crate::config_types::Tui;
 use crate::config_types::UriBasedFileOpener;
+use crate::features::Feature;
+use crate::features::FeatureOverrides;
+use crate::features::Features;
+use crate::features::FeaturesToml;
 use crate::git_info::resolve_root_git_project_for_trust;
 use crate::model_family::ModelFamily;
 use crate::model_family::derive_default_model_family;
@@ -218,6 +222,9 @@ pub struct Config {
     /// Include the `view_image` tool that lets the agent attach a local image path to context.
     pub include_view_image_tool: bool,
 
+    /// Centralized feature flags; source of truth for feature gating.
+    pub features: Features,
+
     /// The active profile name used to derive this `Config` (if any).
     pub active_profile: Option<String>,
 
@@ -794,19 +801,15 @@ pub struct ConfigToml {
     /// Base URL for requests to ChatGPT (as opposed to the OpenAI API).
     pub chatgpt_base_url: Option<String>,
 
-    /// Experimental path to a file whose contents replace the built-in BASE_INSTRUCTIONS.
-    pub experimental_instructions_file: Option<PathBuf>,
-
-    pub experimental_use_exec_command_tool: Option<bool>,
-    pub experimental_use_unified_exec_tool: Option<bool>,
-    pub experimental_use_rmcp_client: Option<bool>,
-    pub experimental_use_freeform_apply_patch: Option<bool>,
-
     pub projects: Option<HashMap<String, ProjectConfig>>,
 
     /// Nested tools section for feature toggles
     pub tools: Option<ToolsToml>,
 
+    /// Centralized feature flags (new). Prefer this over individual toggles.
+    #[serde(default)]
+    pub features: Option<FeaturesToml>,
+
     /// When true, disables burst-paste detection for typed input entirely.
     /// All characters are inserted as they are received, and no buffering
     /// or placeholder replacement will occur for fast keypress bursts.
@@ -817,6 +820,13 @@ pub struct ConfigToml {
 
     /// Tracks whether the Windows onboarding screen has been acknowledged.
     pub windows_wsl_setup_acknowledged: Option<bool>,
+
+    /// Legacy, now use features
+    pub experimental_instructions_file: Option<PathBuf>,
+    pub experimental_use_exec_command_tool: Option<bool>,
+    pub experimental_use_unified_exec_tool: Option<bool>,
+    pub experimental_use_rmcp_client: Option<bool>,
+    pub experimental_use_freeform_apply_patch: Option<bool>,
 }
 
 impl From<ConfigToml> for UserSavedConfig {
@@ -980,9 +990,9 @@ impl Config {
             config_profile: config_profile_key,
             codex_linux_sandbox_exe,
             base_instructions,
-            include_plan_tool,
-            include_apply_patch_tool,
-            include_view_image_tool,
+            include_plan_tool: include_plan_tool_override,
+            include_apply_patch_tool: include_apply_patch_tool_override,
+            include_view_image_tool: include_view_image_tool_override,
             show_raw_agent_reasoning,
             tools_web_search_request: override_tools_web_search_request,
         } = overrides;
@@ -1005,6 +1015,15 @@ impl Config {
             None => ConfigProfile::default(),
         };
 
+        let feature_overrides = FeatureOverrides {
+            include_plan_tool: include_plan_tool_override,
+            include_apply_patch_tool: include_apply_patch_tool_override,
+            include_view_image_tool: include_view_image_tool_override,
+            web_search_request: override_tools_web_search_request,
+        };
+
+        let features = Features::from_config(&cfg, &config_profile, feature_overrides);
+
         let sandbox_policy = cfg.derive_sandbox_policy(sandbox_mode);
 
         let mut model_providers = built_in_model_providers();
@@ -1050,13 +1069,13 @@ impl Config {
 
         let history = cfg.history.unwrap_or_default();
 
-        let tools_web_search_request = override_tools_web_search_request
-            .or(cfg.tools.as_ref().and_then(|t| t.web_search))
-            .unwrap_or(false);
-
-        let include_view_image_tool = include_view_image_tool
-            .or(cfg.tools.as_ref().and_then(|t| t.view_image))
-            .unwrap_or(true);
+        let include_plan_tool_flag = features.enabled(Feature::PlanTool);
+        let include_apply_patch_tool_flag = features.enabled(Feature::ApplyPatchFreeform);
+        let include_view_image_tool_flag = features.enabled(Feature::ViewImageTool);
+        let tools_web_search_request = features.enabled(Feature::WebSearchRequest);
+        let use_experimental_streamable_shell_tool = features.enabled(Feature::StreamableShell);
+        let use_experimental_unified_exec_tool = features.enabled(Feature::UnifiedExec);
+        let use_experimental_use_rmcp_client = features.enabled(Feature::RmcpClient);
 
         let model = model
             .or(config_profile.model)
@@ -1164,19 +1183,14 @@ impl Config {
                 .chatgpt_base_url
                 .or(cfg.chatgpt_base_url)
                 .unwrap_or("https://chatgpt.com/backend-api/".to_string()),
-            include_plan_tool: include_plan_tool.unwrap_or(false),
-            include_apply_patch_tool: include_apply_patch_tool
-                .or(cfg.experimental_use_freeform_apply_patch)
-                .unwrap_or(false),
+            include_plan_tool: include_plan_tool_flag,
+            include_apply_patch_tool: include_apply_patch_tool_flag,
             tools_web_search_request,
-            use_experimental_streamable_shell_tool: cfg
-                .experimental_use_exec_command_tool
-                .unwrap_or(false),
-            use_experimental_unified_exec_tool: cfg
-                .experimental_use_unified_exec_tool
-                .unwrap_or(false),
-            use_experimental_use_rmcp_client: cfg.experimental_use_rmcp_client.unwrap_or(false),
-            include_view_image_tool,
+            use_experimental_streamable_shell_tool,
+            use_experimental_unified_exec_tool,
+            use_experimental_use_rmcp_client,
+            include_view_image_tool: include_view_image_tool_flag,
+            features,
             active_profile: active_profile_name,
             windows_wsl_setup_acknowledged: cfg.windows_wsl_setup_acknowledged.unwrap_or(false),
             disable_paste_burst: cfg.disable_paste_burst.unwrap_or(false),
@@ -1309,6 +1323,7 @@ pub fn log_dir(cfg: &Config) -> std::io::Result<PathBuf> {
 mod tests {
     use crate::config_types::HistoryPersistence;
     use crate::config_types::Notifications;
+    use crate::features::Feature;
 
     use super::*;
     use pretty_assertions::assert_eq;
@@ -1436,6 +1451,93 @@ exclude_slash_tmp = true
         Ok(())
     }
 
+    #[test]
+    fn profile_legacy_toggles_override_base() -> std::io::Result<()> {
+        let codex_home = TempDir::new()?;
+        let mut profiles = HashMap::new();
+        profiles.insert(
+            "work".to_string(),
+            ConfigProfile {
+                include_plan_tool: Some(true),
+                include_view_image_tool: Some(false),
+                ..Default::default()
+            },
+        );
+        let cfg = ConfigToml {
+            profiles,
+            profile: Some("work".to_string()),
+            ..Default::default()
+        };
+
+        let config = Config::load_from_base_config_with_overrides(
+            cfg,
+            ConfigOverrides::default(),
+            codex_home.path().to_path_buf(),
+        )?;
+
+        assert!(config.features.enabled(Feature::PlanTool));
+        assert!(!config.features.enabled(Feature::ViewImageTool));
+        assert!(config.include_plan_tool);
+        assert!(!config.include_view_image_tool);
+
+        Ok(())
+    }
+
+    #[test]
+    fn feature_table_overrides_legacy_flags() -> std::io::Result<()> {
+        let codex_home = TempDir::new()?;
+        let mut entries = BTreeMap::new();
+        entries.insert("plan_tool".to_string(), false);
+        entries.insert("apply_patch_freeform".to_string(), false);
+        let cfg = ConfigToml {
+            features: Some(crate::features::FeaturesToml { entries }),
+            ..Default::default()
+        };
+
+        let config = Config::load_from_base_config_with_overrides(
+            cfg,
+            ConfigOverrides::default(),
+            codex_home.path().to_path_buf(),
+        )?;
+
+        assert!(!config.features.enabled(Feature::PlanTool));
+        assert!(!config.features.enabled(Feature::ApplyPatchFreeform));
+        assert!(!config.include_plan_tool);
+        assert!(!config.include_apply_patch_tool);
+
+        Ok(())
+    }
+
+    #[test]
+    fn legacy_toggles_map_to_features() -> std::io::Result<()> {
+        let codex_home = TempDir::new()?;
+        let cfg = ConfigToml {
+            experimental_use_exec_command_tool: Some(true),
+            experimental_use_unified_exec_tool: Some(true),
+            experimental_use_rmcp_client: Some(true),
+            experimental_use_freeform_apply_patch: Some(true),
+            ..Default::default()
+        };
+
+        let config = Config::load_from_base_config_with_overrides(
+            cfg,
+            ConfigOverrides::default(),
+            codex_home.path().to_path_buf(),
+        )?;
+
+        assert!(config.features.enabled(Feature::ApplyPatchFreeform));
+        assert!(config.features.enabled(Feature::StreamableShell));
+        assert!(config.features.enabled(Feature::UnifiedExec));
+        assert!(config.features.enabled(Feature::RmcpClient));
+
+        assert!(config.include_apply_patch_tool);
+        assert!(config.use_experimental_streamable_shell_tool);
+        assert!(config.use_experimental_unified_exec_tool);
+        assert!(config.use_experimental_use_rmcp_client);
+
+        Ok(())
+    }
+
     #[test]
     fn config_honors_explicit_file_oauth_store_mode() -> std::io::Result<()> {
         let codex_home = TempDir::new()?;
@@ -2120,6 +2222,7 @@ model_verbosity = "high"
                 use_experimental_unified_exec_tool: false,
                 use_experimental_use_rmcp_client: false,
                 include_view_image_tool: true,
+                features: Features::with_defaults(),
                 active_profile: Some("o3".to_string()),
                 windows_wsl_setup_acknowledged: false,
                 disable_paste_burst: false,
@@ -2183,6 +2286,7 @@ model_verbosity = "high"
             use_experimental_unified_exec_tool: false,
             use_experimental_use_rmcp_client: false,
             include_view_image_tool: true,
+            features: Features::with_defaults(),
             active_profile: Some("gpt3".to_string()),
             windows_wsl_setup_acknowledged: false,
             disable_paste_burst: false,
@@ -2261,6 +2365,7 @@ model_verbosity = "high"
             use_experimental_unified_exec_tool: false,
             use_experimental_use_rmcp_client: false,
             include_view_image_tool: true,
+            features: Features::with_defaults(),
             active_profile: Some("zdr".to_string()),
             windows_wsl_setup_acknowledged: false,
             disable_paste_burst: false,
@@ -2325,6 +2430,7 @@ model_verbosity = "high"
             use_experimental_unified_exec_tool: false,
             use_experimental_use_rmcp_client: false,
             include_view_image_tool: true,
+            features: Features::with_defaults(),
             active_profile: Some("gpt5".to_string()),
             windows_wsl_setup_acknowledged: false,
             disable_paste_burst: false,