class PolicyIndexRow(BaseModel):    """One row of the corpus index: one policy, six business fields."""    doc_id: str              # the file, so an answer can cite where it came from    policy_number: str       # what the business types into its own systems    client_name: str         # the party the policy is written for    product: str             # one of eleven, and the list never changes    effective_date: date     # the day the cover starts    renewal_date: date       # the day it lapses if nobody acts    premium_eur: float       # the number the finance team filters on