Pass a `slot_id` from get_availability. Confirm the venue, date, time and party size
    with the person before calling this, and do not call it speculatively: there is no
    cancel tool, so a booking made by mistake has to be undone by the guest phoning the
    restaurant.

    Calling it twice with identical arguments is safe and returns the same reservation
    rather than taking a second table. Changing the slot or the guest makes it a
    different booking, so re-read availability rather than editing the arguments to
    "retry".

    `phone` is optional here but required by some venues; omitting it can come back as
    `guest_field_required`. `note` reaches the restaurant as the reservation's note.

    `source` is where you found this venue: if the restaurant's own website told you a
    value to pass (in its markup or llms.txt), send it here so the restaurant can see its
    own site drove the booking. Leave it out if you did not arrive through one.

    `reservation_id` is for your own use, to read the booking back with get_reservation.
    It is not a confirmation number the venue knows, so do not read it out to the guest:
    tell them the restaurant, date, time and party size instead.