Filter custom post types with terms in the admin area

[sanketio]

Adds taxonomy filter dropdowns to custom post type list tables in wp-admin, controlled via Screen Options. Filters are hidden by default; users opt in per-taxonomy. Enabled filters appear in a dedicated second row below the built-in date/category row. The preference is persisted per-user per-screen via user meta.

Testing instructions

1. Register a CPT with at least two custom taxonomies (e.g. movie with actor and genre), add a few terms to each, and create some posts assigned to those terms.
2. Navigate to Posts → Movies (or whatever the CPT slug is).
3. Confirm the list table looks identical to a standard list table — no extra row, no new dropdowns.
4. Open Screen Options. Confirm a new "Filters" fieldset is present listing your taxonomies.
5. Check one taxonomy (e.g. "Actors"). Confirm a dropdown appears immediately in the second row below the built-in filters — no page reload required.
6. Select a term from the dropdown and click Filter. Confirm the URL contains ?actor=keanu-reeves (slug, not ID) and only matching posts are shown.
7. Check a second taxonomy. Confirm both dropdowns appear in the same second row with the Filter button at the end — not on a third line.
8. Uncheck all taxonomy checkboxes. Confirm the second row disappears entirely.
9. Reload the page. Confirm your checkbox preferences were remembered.
10. With a term selected in the URL (e.g. ?actor=keanu-reeves), uncheck Actors in Screen Options. Reload that URL. Confirm the filter is silently dropped and all posts are shown (not zero results).
11. Navigate to the front-end CPT archive. Confirm no change in front-end query behaviour.

Trac ticket: https://core.trac.wordpress.org/ticket/62854

Use of AI Tools

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