Add code_mode experimental feature (#13418)

A much narrower and more isolated (no node features) version of js_repl

codex-rs/core/src/tools/spec.rs

@@ -67,6 +67,7 @@ pub(crate) struct ToolsConfig {
     pub search_tool: bool,
     pub request_permission_enabled: bool,
     pub request_permissions_tool_enabled: bool,
+    pub code_mode_enabled: bool,
     pub js_repl_enabled: bool,
     pub js_repl_tools_only: bool,
     pub collab_tools: bool,
@@ -94,6 +95,7 @@ impl ToolsConfig {
             session_source,
         } = params;
         let include_apply_patch_tool = features.enabled(Feature::ApplyPatchFreeform);
+        let include_code_mode = features.enabled(Feature::CodeMode);
         let include_js_repl = features.enabled(Feature::JsRepl);
         let include_js_repl_tools_only =
             include_js_repl && features.enabled(Feature::JsReplToolsOnly);
@@ -170,6 +172,7 @@ impl ToolsConfig {
             search_tool: include_search_tool,
             request_permission_enabled,
             request_permissions_tool_enabled,
+            code_mode_enabled: include_code_mode,
             js_repl_enabled: include_js_repl,
             js_repl_tools_only: include_js_repl_tools_only,
             collab_tools: include_collab_tools,
@@ -196,6 +199,12 @@ impl ToolsConfig {
         self.web_search_config = web_search_config;
         self
     }
+
+    pub fn for_code_mode_nested_tools(&self) -> Self {
+        let mut nested = self.clone();
+        nested.code_mode_enabled = false;
+        nested
+    }
 }
 
 fn supports_image_generation(model_info: &ModelInfo) -> bool {
@@ -1523,6 +1532,32 @@ fn create_js_repl_reset_tool() -> ToolSpec {
     })
 }
 
+fn create_code_mode_tool(enabled_tool_names: &[String]) -> ToolSpec {
+    const CODE_MODE_FREEFORM_GRAMMAR: &str = r#"
+start: source
+source: /[\s\S]+/
+"#;
+
+    let enabled_list = if enabled_tool_names.is_empty() {
+        "none".to_string()
+    } else {
+        enabled_tool_names.join(", ")
+    };
+    let description = format!(
+        "Runs JavaScript in a Node-backed `node:vm` context. This is a freeform tool: send raw JavaScript source text (no JSON/quotes/markdown fences). Direct tool calls remain available while `code_mode` is enabled. Inside JavaScript, call nested tools with `await tools[name](args)` or identifier wrappers like `await shell(args)` when the tool name is a valid JS identifier. Nested tool calls resolve to arrays of content items. Function tools require JSON object arguments. Freeform tools require raw strings. Use synchronous `add_content(value)` with a content item or content-item array, including `add_content(await exec_command(...))`, to return the same content items a direct tool call would expose to the model. Only content passed to `add_content(value)` is surfaced back to the model. Enabled nested tools: {enabled_list}."
+    );
+
+    ToolSpec::Freeform(FreeformTool {
+        name: "code_mode".to_string(),
+        description,
+        format: FreeformToolFormat {
+            r#type: "grammar".to_string(),
+            syntax: "lark".to_string(),
+            definition: CODE_MODE_FREEFORM_GRAMMAR.to_string(),
+        },
+    })
+}
+
 fn create_list_mcp_resources_tool() -> ToolSpec {
     let properties = BTreeMap::from([
         (
@@ -1829,6 +1864,7 @@ pub(crate) fn build_specs(
 ) -> ToolRegistryBuilder {
     use crate::tools::handlers::ApplyPatchHandler;
     use crate::tools::handlers::ArtifactsHandler;
+    use crate::tools::handlers::CodeModeHandler;
     use crate::tools::handlers::DynamicToolHandler;
     use crate::tools::handlers::GrepFilesHandler;
     use crate::tools::handlers::JsReplHandler;
@@ -1865,11 +1901,32 @@ pub(crate) fn build_specs(
         default_mode_request_user_input: config.default_mode_request_user_input,
     });
     let search_tool_handler = Arc::new(SearchToolBm25Handler);
+    let code_mode_handler = Arc::new(CodeModeHandler);
     let js_repl_handler = Arc::new(JsReplHandler);
     let js_repl_reset_handler = Arc::new(JsReplResetHandler);
     let artifacts_handler = Arc::new(ArtifactsHandler);
     let request_permission_enabled = config.request_permission_enabled;
 
+    if config.code_mode_enabled {
+        let nested_config = config.for_code_mode_nested_tools();
+        let (nested_specs, _) = build_specs(
+            &nested_config,
+            mcp_tools.clone(),
+            app_tools.clone(),
+            dynamic_tools,
+        )
+        .build();
+        let mut enabled_tool_names = nested_specs
+            .into_iter()
+            .map(|spec| spec.spec.name().to_string())
+            .filter(|name| name != "code_mode")
+            .collect::<Vec<_>>();
+        enabled_tool_names.sort();
+        enabled_tool_names.dedup();
+        builder.push_spec(create_code_mode_tool(&enabled_tool_names));
+        builder.register_handler("code_mode", code_mode_handler);
+    }
+
     match &config.shell_type {
         ConfigShellToolType::Default => {
             builder.push_spec_with_parallel_support(