Design a collaborative, editable code notebook service with an execution service and a proxy that fetches execution results and returns them to the browser. Users may upload custom function JAR files with a fully qualified class and method name, then submit requests to run that function with arguments. Define RESTful endpoints and request and response schemas for uploading code, submitting executions, fetching logs and results, and cancelling. Discuss sandboxing, dependency management, resource limits, concurrency, and result streaming.