Turn an open-ended idea into a PRD plus a runnable definition of done. Use when a developer wants to start a new feature, "file a PRD", "spec out" or "scope" an idea, think through what to build, or kick off the harness for a piece of work. Produces prds/<feature>/prd.md + an executable prds/<feature>/run-prd-test.sh on a prd/<author-slug>/<feature> branch. The one human-attentive skill in the chain.