Writing pulumi stack code in c# for pulumi up command. how do i set a breakpoint and debug it? it seems i can invoke the code by cli (pulumi up) only.

Let me know if this is what you are looking for https://www.pulumi.com/blog/next-level-iac-breakpoint-debugging/

so I need extra setup. is there doc for Jetbrain Rider IDE?

Not that I know of