Hi, I just found out when I switched from "motor" to "muscle" type for actuators, the program's threading model was changed as well. I cannot find any documentation on this, but it seems to me several simulation threads would work on different mjData* of their own. This wasn't the case with "motor" type, where several threads were working on the same mjData. Would someone elaborate what is happening here and why, and more importantly how I should write mjcb_control() differently in these two cases?