I shipped a crypto fintech solo last year: 13 apps, three databases, Kubernetes, real money, in about 70 days, with AI agents doing most of the typing. The thing that made it possible was not a better model. It was refusing to prompt.
Here is the problem with prompting a capable agent. It has no memory between sessions. Every conversation starts at zero. Ask it to "add authentication" and it will confidently write 500 lines that compile, pass a lint, and solve a slightly different problem than the one you had, using an architecture you never agreed to. The more capable the model, the further a vague instruction carries it in the wrong direction.
So I stopped prompting and started specifying. I packaged the workflow I settled on into an open-source kit for the Pi coding agent, called pi-sdd-kit. This post is about the two design decisions that actually earned their keep. The rest is detail.
The shape of it
Spec-driven development (SDD) inverts the usual order. The specification is the primary artifact and the code is a consequence of it, not the other way around. In pi-sdd-kit that means every feature moves through a fixed pipeline, with a human approval gate between each phase:
