refactor: several improvements (#132)

- js export expression
- check args regarding run-agent/run-tool

tools/execute_js_code.js

@@ -4,7 +4,7 @@
  * @property {string} code - Javascript code to execute, such as `console.log("hello world")`
  * @param {Args} args
  */
-exports.run = function run({ code }) {
+exports.run = function ({ code }) {
   let output = "";
   const oldStdoutWrite = process.stdout.write.bind(process.stdout);
   process.stdout.write = (chunk, _encoding, callback) => {