i don't really have time to pair today (maybe someone else does?), but happy to answer questions. i believe that it would be using code similar to https://github.com/pantsbuild/pants/blob/master/src/rust/engine/process_execution/src/speculate.rs#L37 in either https://github.com/pantsbuild/pants/blob/7f4ef60d103cac833451b5af2944e1c83a57ba26/src/rust/engine/process_execution/src/local.rs#L273-L281 or https://github.com/pantsbuild/pants/blob/7f4ef60d103cac833451b5af2944e1c83a57ba26/src/rust/engine/process_execution/src/local.rs#L236-L240