Build a feature with superpowers: agree, plan, test first, then prove it

Four skills from Jesse Vincent's superpowers make Claude Code agree with you on what to build, write a plan, see each test fail before the code, and run the whole suite before it says done.

Our run, 2026-09-28. Asked to split GST into CGST and SGST "half each", Claude read the code and asked what happens when the GST is an odd number of paise, before writing any code. The request never mentions it.