Pure: nothing is stored. Returns `profile` (pass it to ads_check) and `mandate`
    (what /enforce/check evaluates).

    Args:
        account_ids: advertiserAccountId / profileId values the agent may act on
        brands: brands the agent may touch
        daily_budget_cap_usd: largest daily campaign budget; above it: forbid
        hold_threshold_usd: above it a person named in `approvers` must approve
        total_daily_budget_cap_usd: sum of daily budgets on the account after a change
        period_budget_cap_usd: largest lifetime or monthly budget
        max_bid_usd: largest bid
        max_bid_change_percent: largest bid change per step, in percent
        valid_from: RFC 3339 UTC second
        valid_until: RFC 3339 UTC second; after it every call is forbidden
        tools: allowed tool names (default: all documented in ads_onboard)
        mandate_id: your identifier for this mandate
        principal_did: the agency's DID
        principal_public_key: the agency's Ed25519 public key, hex
        approvers: [{"did", "public_key", "role"}] who may approve a hold