- Define ProjectRuntime interface with unified task execution contract\n- Implement IPC protocol for host-worker communication (messages, streaming, heartbeats)\n- Add InProcessRuntime for synchronous in-process task execution\n- Add ChildProcessRuntime with isolated worker processes for sandboxed execution\n- Implement ProjectManager to coordinate runtime selection and task lifecycle\n- Update engine exports to expose runtime APIs\n- Add comprehensive tests for all runtime implementations and IPC protocol
