Preserve existing store labels when updating attribute option via API

[mimou78]

Description (*)

This PR fixes an issue where updating a product attribute option via the API endpoint:

PUT /V1/products/attributes/byAttributeCode/options/byOptionId

would unintentionally erase store-specific labels that were not included in the payload.

Magento's current implementation of \Magento\Eav\Model\Entity\Attribute\OptionManagement::saveOption() overwrites all store_labels for an option when updating just one, instead of merging them. This fix introduces logic to preserve existing store labels and only update those explicitly provided.

Related Pull Requests

Fixed Issues (if relevant)

1. Fixes Attribute Option Label Gets Overwritten When Updating Store Labels #40093

Manual testing scenarios (*)

1. Create an attribute option with multiple store labels (e.g., for France and Germany).
2. Use the API to update only one store label:

 {
     "option_id": 1234,
     "store_labels": [
       {
         "store_id": 2,
         "label": "Bleu updated"
       }
     ]
   }

3. Use the API again to update another store label only:

{
  "option_id": 1234,
  "store_labels": [
    {
      "store_id": 3,
      "label": "Blau updated"
    }
  ]
}

4. Expected result: both store labels (store 2 and store 3) remain intact and updated accordingly.

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

[m2-assistant]

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[mimou78]

@magento run all tests

[mimou78]

@magento run Unit Tests

[mimou78]

@magento run Static Tests

[mimou78]

@magento run Integration Tests

[mimou78]

@magento run Functional Tests CE

[mimou78]

@magento run Functional Tests B2B

[mimou78]

@magento run all test

[magento-automated-testing]

Failed to run the builds. Please try to re-run them later.

[mimou78]

@magento run all tests

[engcom-Bravo]

Hi @mimou78,

Thank you for your contribution! The Magento core engineering team is working on the issue which you have addressed in this PR. Team will cherry pick the commits from your PR and may do further implementation to cover few more scenarios as needed. We will reach out to you if we need more information. For now, you can pause work on this PR.

Thank you once again!