If you have multiple virtual threads issuing non-atomic commands that must be run together and not interwoven, how does the scheduler know when it's ok to yield

If you have multiple virtual threads issuing non-atomic commands that must be run together and not interwoven, how does the scheduler know when it's ok to yield one thread to another without explicit support? How can you set a shader and then draw a mesh each in two virtual threads without possibly interweaving their execution, for example?