[Issue] Fix: propagate stock validation message in QuantityValidator error info #40569
Description
This issue is automatically created based on existing pull request: #40556: Fix: propagate stock validation message in QuantityValidator error info
Description (*)
- Fix missing error message when QuantityValidator reports a stock error that already has a stockStateResult with hasError = true
- Previously, addErrorInfo() was called without a message, causing silent errors in consumers like the GraphQL cart mutations
- Now propagates $stockResult->getMessage() with a fallback to the default "out of stock" message
Manual testing scenarios (*)
- Add an out-of-stock product to cart via GraphQL and verify the error response contains a descriptive message
- Verify standard storefront "out of stock" behavior is unchanged
- Run existing CatalogInventory unit/integration tests
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)