JoystickGremlin

Produce a grounded design document (PRD + spec hybrid, minus market/corporate framing) for a new feature in an EXISTING codebase, by interviewing the user one question at a time and exploring the real code before each decision. Use this WHENEVER the user wants to plan, design, or spec a feature in a codebase before building it — e.g. "design doc for X", "spec out X", "let's design X before we build it", "write a design document", "grill me on this feature and write it up", or when they describe a non-trivial feature and start reasoning about how it should work. Trigger even if the user does not say the words "design document". Do NOT trigger when the user just wants to start implementing or fixing code now — this skill stops at the document and never writes feature code.