[irozum]

Trac ticket: https://core.trac.wordpress.org/ticket/50675

Summary

What: Adds PHPUnit coverage for WP_REST_Attachments_Controller::edit_media_item() copying data from the original attachment to the edited one. This is a test-only change; it touches no src/ files and adds no production behaviour.

Context: Follow-up to [48510], which added this behaviour. Nothing in trunk covers the fallback path: the existing test_edit_image_updates_attachment_fields() (#64035) only passes every field explicitly in the request.

Cases covered:

• Request omits all fields: the new attachment inherits title, caption, description and alt text from the original.
• Original has no alt text: no empty _wp_attachment_image_alt meta row is created on the new attachment.
• Request supplies only title and alt_text: those win, while the omitted caption and description are still inherited (mixed precedence).

Verification: Each test was confirmed to fail when the matching code in edit_media_item() was temporarily broken (fallbacks removed, alt fallback removed, empty-alt guard removed, ??= changed to =, alt ternary swapped), then restored.

Out of scope: The EXIF image_meta merge from the same changeset; it depends on GD/Imagick EXIF output and could be a follow-up.

Use of AI Tools

This PR was prepared with Claude Code (Claude Sonnet 5.5), which wrote the tests and ran the verification above.

This pull request is for code review only. Please keep all discussion in the Trac ticket.

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