I’m trying to debug very slow sandbox requirements.pex building. Is there a flag to see the output of what it’s trying to do, as it’s doing it? E.g. what packages are being fetched, if its using a source package and therefore compiling from scratch, etc?

I think the usual debugging/troubleshooting suggested by pants should work to figure it out e.g.

--keep-sandboxes

https://www.pantsbuild.org/docs/troubleshooting