Fix Product Links always being processed in afterSave

[OddScenario]

Description (*)

Magento\Catalog\Model\Product::afterSave() unconditionally called getLinkInstance()->saveProductRelations($this) on every save, re-processing product links even when the caller explicitly indicated that links should be left untouched. Magento\Catalog\Model\ProductRepository already exposes an ignore_links_flag to opt out of link pre-processing, but afterSave() never checked that flag — so the unchanged product_links were still re-processed and written to the database on every save.

This becomes visible under concurrent saves against the same product (e.g. updating multiple storeviews in parallel). The post-processing races with itself and fails with:

HTTP 400 — "The linked products data is invalid. Verify the data and try again."

even when the PUT body contains no product_links at all.

This PR makes afterSave() respect ignore_links_flag, and updates ProductRepository::processLinks() to set the ignore_links_flag when the links are null.

Manual testing scenarios (*)

Preconditions: a Magento instance with ≥2 storeviews and at least 1 product that has related / upsell / crosssell links configured (e.g. 24-MB01 from sample data).

1. Run the script below against the instance.
2. Before this fix: at least one response returns HTTP 400 with "The linked products data is invalid. Verify the data and try again.", even though no product_links are in any PUT body.
3. After this fix: product_links are only processed when present in the PUT body.

  const BASE_URL = 'https://magento.test';
  const TOKEN    = '<admin-or-integration-token>';
  const SKU      = '24-MB01';
  const STORE_CODES = ['all', 'store_1', 'store_2', 'store_3', 'store_4', 'store_5', 'store_6', 'store_7', `store_8`];

  const randomName = () =>
    `perf-test-${Math.random().toString(36).slice(2, 10)}`;

  const putForStore = (store) =>
    fetch(`${BASE_URL}/rest/${store}/V1/products/${encodeURIComponent(SKU)}`, {
      method: 'PUT',
      headers: {
        Authorization: `Bearer ${TOKEN}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({ product: { name: randomName() } }),
    }).then(async (res) => ({
      store,
      status: res.status,
      body: await res.text(),
    }));

  const results = await Promise.all(STORE_CODES.map(putForStore));

  for (const { store, status, body } of results) {
    console.log(`[${store}] ${status} ${body.slice(0, 200)}`);
  }

  const failed = results.filter((r) => r.status >= 400);
  process.exit(failed.length ? 1 : 0);

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)

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[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email psirt@adobe.com.

[OddScenario]

@magento run all tests

[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email psirt@adobe.com.

[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email psirt@adobe.com.

[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email psirt@adobe.com.

[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email psirt@adobe.com.