Fix duplicate meta and closed comment status when adding a custom field to an auto-draft

[shameemreza]

Adding a custom field to a new post (auto-draft) through the legacy Custom Fields meta box inserts the meta twice and switches the post's comment and ping status to closed.

wp_ajax_add_meta() promotes the auto-draft to a draft through edit_post(). That function reads metakeyinput and metavalue from $_POST, which the AJAX request body contains, so the meta is added there first. Control then returns to wp_ajax_add_meta(), which calls add_meta() again. The same edit_post() call passes no comment_status or ping_status, so _wp_translate_postdata() defaults both to closed. The block editor only sends comment_status over the REST API when the Discussion panel was changed, so the closed status sticks after publishing.

This change promotes the auto-draft with wp_update_post() instead. The meta is inserted exactly once, the post keeps its comment and ping status, and the _edit_last meta is still set as before.

Includes unit tests covering both symptoms. They fail against the current code and pass with this change:

1) test_adding_meta_to_an_auto_draft_should_not_duplicate_the_meta
Failed asserting that two arrays are identical.
 Array &0 (
     0 => 'testvalue'
+    1 => 'testvalue'
 )

2) test_adding_meta_to_an_auto_draft_should_not_change_the_comment_and_ping_status
The comment status of the post should not have changed.
-'open'
+'closed'

To reproduce manually: on a clean install with the Custom Fields panel enabled, open Posts > Add New, add a custom field before saving, then check wp_postmeta and the post's comment_status.

Trac ticket: https://core.trac.wordpress.org/ticket/66016

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Used for: diagnosis, draft patch, and test suggestions. I reviewed, tested, and edited the final change.

---

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