majorleaf/coX ? reverse-engineered prompt

Build me a secure online code runner API for JavaScript that lets me send code over HTTP, get back a job ID right away, and then check the job status while it runs in the background. I want the code to execute inside a locked down Docker container so untrusted code cannot touch the host, cannot use the network, has tight memory and CPU limits, runs as a non root user, and gets killed after a short timeout.

I also want live progress updates while the code runs, like which line is being executed, how long it has been running, and the final output. Use WebSockets so a client can subscribe to a job and receive progress and done events in real time, even if they join a little late. Keep it simple for now, just JavaScript execution with jobs stored in memory, and if you need to check current docs for any library details, go ahead and look them up online.