closePosition

async def closePosition(marketId: int, size: float=None, priceThreshold: float=0):
    existing = await retrieveExistingPosition(marketId)
    if existing is None:
        print('No position to close')
        return None
    original_size = existing.nominalSize
    orderId = existing.position_id
    print('position', existing)
    if size is None:
        size_to_reduce = original_size
        print(f'Closing full position (size: {original_size})')
    else:
        size_to_reduce = size
        print(f'Partially closing position (reducing size by {size} from {original_size})')
    await reduceOrder(marketId, orderId, size_to_reduce, priceThreshold)
    new_size = original_size - size_to_reduce
    existing.nominalSize = new_size
    print(f'Transaction submitted successfully (size: {original_size} → {new_size})')
    return MessageToDict(existing, always_print_fields_with_no_presence=True)