feat(mcp): platform extension for "code mode" MCP tool calling (#6030)

Co-authored-by: Michael Neale <michael.neale@gmail.com>

crates/goose/src/agents/extension.rs

@@ -1,4 +1,5 @@
 use crate::agents::chatrecall_extension;
+use crate::agents::code_execution_extension;
 use crate::agents::extension_manager_extension;
 use crate::agents::skills_extension;
 use crate::agents::todo_extension;
@@ -87,6 +88,18 @@ pub static PLATFORM_EXTENSIONS: Lazy<HashMap<&'static str, PlatformExtensionDef>
             },
         );
 
+        map.insert(
+            code_execution_extension::EXTENSION_NAME,
+            PlatformExtensionDef {
+                name: code_execution_extension::EXTENSION_NAME,
+                description: "Execute JavaScript code in a sandboxed environment",
+                default_enabled: false,
+                client_factory: |ctx| {
+                    Box::new(code_execution_extension::CodeExecutionClient::new(ctx).unwrap())
+                },
+            },
+        );
+
         map
     },
 );