Tree-walking ECMAScript interpreter built on ecma-syntax-cat. v0.6.0 adds `await` evaluator dispatch + async function call wrapping (async track chunk 3 of 5-7): `await Resolved(v)` -> `v`, `await Rejected(v)` -> throw `v`, `await Pending` -> TypeError (no continuation in the synchronous tree-walking model), `await non_promise` -> pass through. Calling an async function (`FunctionDef::is_async()` flag, threaded from `Function::is_async()` / `ArrowFunction::is_async()`) wraps the body's normal completion in a `Resolved` promise and its throw completion in a `Rejected` promise.