ProductVariationContext is causing extra generate sample images to be generated

I'm elevating this issue as critical due to the following scenario / behavior:

(1) Drupal 9 with Layout Builder enabled.
(2) Drupal Commerce with a number of product variations, each of which has media entities associated with them to manage product image galleries
(3) media entity items that manage a specific file type limited to CAD files, also associated with a subset of product variations
(4) Currently approximately a dozen product types and variations configured, will have more due to the complex nature of the products involved with this project.
(5) Remote object store utilizing Flysystem for object store interface (in our case, Google Cloud Storage for staging and production, MinIO for local developer environments)
(6) Layout Builder is not in use on product add pages.

When pulling up a product add page and selecting ANY configured product, the call to ProductVariationContext::getRuntimeContexts() results in up to 230 files and images being created ON THE OBJECT STORE when lanuching a product add page, specifically when the above mentioned method hits $value = $this->productVariationStorage->createWithSampleValues($product_type->getVariationTypeId()).

Due to the inherent latency involved when writing images to the remote object store, the generation of 200 files, while perhaps temporary, makes the product add experience unusable. The more product types and variations that are added, the longer the latency.

In addition, temporary sample content files get created for file types that have nothing to do with the product at hand, and those temporary files do not respect the file extensions configured for the file fields in question.

This patch fixed exactly the same issue with dummy generated paragraphs on "Add product" page https://www.drupal.org/project/commerce/issues/3209625

I'll fix this.

Also, I am fairly certain that "Show content preview" is a client side toggle. So this is a Drupal core problem as well, for a lot of images.

Note: We cannot check for "Show content preview" due to the fact it is client side (local storage.) I can confirm that generating sample values created random files. We can create a baseline test for this, at least.

Linking #3099968: Layout builder incorrectly resolves global contexts values when viewing layouts. Once of the fixes is to properly implement ::getAvailableContexts like NodeRouteContext. But it sounds like that could create bugs. Linking for later reference.

I don't know how easily we can fix this in Commerce itself. The fixes in #3220015: ProductVariationContext improperly implements ContextProviderInterface will improve additional runs for calculating context value.

This may be a Drupal core problem that anyone using Nodes with image fields would also experience. For instance, on a Standard profile. I installed Layout Builder. Enabled Layout Builder for Article content type, which has an image. In my manual testing, I only had one image be reproduced. So maybe there is something in NodeRouteContext I can leverage.

I think I found a fix! Working on a MR shortly. Layou Builder has a service for generating sample entities. It's used in \Drupal\layout_builder\Plugin\SectionStorage\DefaultsSectionStorage::getContextsDuringPreview, which is where the Node entity or Product entity is pulled from. This prevents a bunch of random generations.

Product variations are worked in subcontext. If we change to that generation service, the same preview for a bundle will be reused and stop extra image generation.

We should add a test that verifies a variation type with image only generates ONE sample image despite visiting the manage default layout multiple times.

Wrote the test :) There are still 5 files being reported as generated. When I manually tested, I had a product with only 1 variation. I don't know the easiest way to work around this. It might be due to the product itself being generated and EntityReferenceItem's sample generated values.

However, if that is the case, we're now more relatable to Paragraphs and can see what was done there. It's no longer being caused by the variation context

I'm going to go ahead and merge this. We have test coverage and it had a bunch of manual debugging. Merging this also helps push #3220015: ProductVariationContext improperly implements ContextProviderInterface forward for more fixes.

Thank you @mglaman!