Spec is where the conversation becomes an artifact. Everything before it — the grill, and any research or prototype detours — lived in a single unbroken session. The spec is the first thing that outlives that session: a written synthesis of what the effort is, why it matters, and what "done" means.
It's produced agent-solo, but never in a vacuum. The spec has to be written while the grill is still warm, in the same window, because a spec is only as good as the understanding behind it — and that understanding is exactly what gets lost when a grill is compressed into a summary and handed to a fresh context.
How it runs
The agent turns the grill into a spec: the problem, the solution, the decisions and their reasoning, and what's explicitly out of scope. Then it stops for the one genuinely collaborative moment in the step — agreeing the test seams with the human.
Seams are the places the work will be tested, and they're chosen on a strict principle: the fewest, at the highest level, that still pin the behavior down. A seam pins what the system does, not how it's built — so the tests survive refactoring instead of ossifying it. This is a decision, not a formality, which is why it's the one point a human is pulled back in before the spec is considered finished.
What gets settled here
Two things. The spec itself — the contract every downstream step inherits. And the test seams — agreed here, and nowhere else. The rule that follows from that agreement is deliberately sharp: no test gets written later at a seam that wasn't confirmed at this step. Testing effort is aimed on purpose, once, with the whole shape in view — not sprinkled reactively during implementation.
Built on
This step is built on Matt Pocock's to-spec skill, run at a checkpoint where the human confirms the test seams before the spec is marked ready.