Collect quote totals at init checkout page and cart page?

Question

i'm using magento v2.4.1. I tried to add the product to the cart programmatically using salesrule_validator_process observer, this is to add a product if a cart rule being applied to the cart:

$quote = $observer->getEvent()->getQuote();
$productId = 15;
$qty = 1;
$product = $this->productRepository->getById($productId, false, $storeId);
$addResult = $quote->addProduct($product,$qty);
$newQuoteItem = $addResult;
$newQuoteItem->setCustomPrice(0);
$newQuoteItem->setOriginalCustomPrice(0);
$newQuoteItem->setBaseTaxCalculationPrice(0);
$newQuoteItem->setTaxCalculationPrice(0);
$newQuoteItem->setNoDiscount(true);
$newQuoteItem->getProduct()->setIsSuperMode(true);
$newQuoteItem->calcRowTotal();

The problem is this observer only fires at quote collect totals, so sometimes is not firing at the checkout cart page or checkout page, is there a way to include the collect totals at the checkout page or checkout cart page when the customer first visit the page ? is it safe to do this ?

Answer 1

This is not the safe way to do this:

you must add product using checkout_submit_before event.

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="checkout_submit_before">
        <observer name="quoteSubmitBefore" instance="namespace\module\Observer\QuoteSubmitBefore" />
    </event>
</config>