This might be overkill. You can terminate gif.js workers fairly easily: _terminate(gif) { gif.abort(); gif.freeWorkers.forEach(w => w.terminate()); } (From https://observablehq.com/d/88a8246df5677bae#GifConverter)

I don't think leaks comes up in practice enough for me to worry about it. The gif render call is triggered by a deliberate human click which is not going to be often.

Sorry, I totally misread this cell's purpose! Somehow I thought it was meant to create compilation threads.

Submitting twice triggers an "RuntimeError: Already running" error in the step cell and dependent cells

thanks fixed.