Analyze this product's already-analyzed TikTok videos and generate a creative brief — content angles, unique selling points, filming recommendations, dos/don'ts, and the top inspiration videos — then save it as a drafted brief and return it.

Each call is a fresh generation that spends model tokens and creates a new brief row, so Idempotency-Key is required: a retried request replays the first result instead of paying for and storing a duplicate. Send X-Dry-Run: true to validate the product without generating.

Returns 404 when the product isn't in this shop, and 422 when the product has no analyzed videos to build a brief from — run video analysis first.