Interview the user relentlessly about a plan or design until reaching shared understanding, resolving each branch of the decision tree, then emitting a Design Notes + Glossary + edge-case block and persisting it to docs/intent/NNNN-<slug>.md for handoff to /to-prd. Use when user wants to stress-test a plan, get grilled on their design, do a pre-PRD design review, challenge an idea before writing it up, or mentions "grill me" or runs /grill-me.
