Guidelines: Extract initial public API methods

[gziolo]

Part of:

• Guidelines: Evolve CPT to enable support for skills, memory, and plans via taxonomy #77230.

Summary

Builds on #77592. Three independent changes that move the Guidelines experiment a step closer to a shape that could plausibly land in WP core.

1. Treat guideline types as a first-class, extensible concept

Today the list of guideline types lives inline inside the post-type registration class, alongside taxonomy registration, hook wiring, and meta logic. That makes it impossible for plugins to add or relabel a type, and impossible for any other code in the project to ask "what types are available?" without reaching into a class internal.

This commit extracts three small functions into a new lib/experimental/guidelines/guidelines.php module and splits them into a public surface plugins can use, and internal hook callbacks they shouldn't:

• wp_guideline_types() — public. The registry of guideline types, filterable via the wp_guideline_types filter so plugins can add or relabel entries. Defaults to artifact and content; everything else can come from the filter.
• _wp_guidelines_ensure_default_type_term() — internal (@access private). Hook callback for save_post_wp_guideline that backfills the 'artifact' term when a guideline is saved without a type. Replaces the static method that previously lived on the post-type class.
• _wp_guidelines_maybe_map_term_label() — internal (@access private). Hook callback for wp_insert_term_data that, when a type term is created lazily from a raw slug, replaces the auto-derived term name with the human-readable title from wp_guideline_types() — so a term created via wp_set_object_terms( …, 'artifact' ) ends up named Artifact instead of artifact.

The leading-underscore + @access private convention follows what WP core uses for hook handlers (e.g. _wp_filter_post_kses) so it's immediately obvious from the source which functions plugins can call. Each function is wrapped in function_exists so the file is a no-op if/when these helpers ever ship in WP core. The post-type class shrinks accordingly and is now responsible only for registration and hook wiring. New unit tests cover each function and the lazy-creation behavior end-to-end.

2. Make the admin look like a real post type, and create headroom for finer permissions

The CPT was registered with two labels (name, singular_name) and capability_type = 'post'. That gave a sparse admin UI (every screen says just "Guidelines") and meant guideline permissions were tied to standard post permissions, with no way to grant access to guidelines without also granting it to all posts.

This commit fills out the full label set (with _x() context for translators) for both the post type and its taxonomy, and switches to capability_type = 'guideline' with map_meta_cap = true. To avoid an unintended access change in this commit, the explicit capabilities array continues to map every meta cap back to the equivalent post cap — so today's behavior is unchanged. The new custom type just gives us room to introduce dedicated edit_guideline / publish_guidelines / etc. primitives (and a "Guideline Editor" role) in a later pass.

3. Lock down write access at the REST layer

After commit 2, users with edit_posts (e.g. editors) could create, update, or delete guidelines through the REST API — the standard permission checks inherited from WP_REST_Posts_Controller say so. Until we have a deliberate role/capability model, the safer default is admin-only writes.

This commit overrides the create / update / delete permission checks on the guidelines REST controller and the revision-restore check on the revisions controller to require manage_options. Reads are intentionally left open to anyone who can edit posts, since editors need to be able to see the guidelines they're expected to follow. Error codes match what core uses (rest_cannot_create / _edit / _delete / _restore) so existing client error handling continues to work.

Test plan

• PHPCS clean across lib/experimental/guidelines/ and phpunit/experimental/guidelines/.
• 44/44 unit tests passing (117 assertions), including 7 new tests covering the extracted public API, the slug-to-label mapping (direct unit cases for each guard + an end-to-end case via wp_set_object_terms), and the previously-failing editor-permission tests for the REST controller.
• Smoke-test the Guidelines admin screens to confirm the new label set renders correctly.
• Confirm via REST (curl or the browser console) that an editor user gets 403 on create/update/delete and that an admin succeeds.

🤖 Generated with Claude Code

[github-actions]

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Co-authored-by: gziolo <gziolo@git.wordpress.org>

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[github-actions]

Flaky tests detected in d90b4ae.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/24903695420
📝 Reported issues:

• [Flaky Test] post title and content are editable and blocks can be inserted #76524 in /test/e2e/specs/editor/various/post-content-focus-mode.spec.js