perf: Avoid eager Gutenberg work on ordinary admin screens

[superdav42]

Goal

Avoid building Ultimate Multisite Gutenberg block metadata and loading Gutenberg support assets on ordinary wp-admin screens that are not block editors.

Evidence

On an authenticated subscriber Dashboard request, Block_Editor_Widget_Manager::handle_element() registered blocks for every Ultimate Multisite UI element. register_block() called each element's fields() method to derive attributes.

Three element field definitions synchronously called get_pages():

• inc/ui/class-current-site-element.php
• inc/ui/class-my-sites-element.php
• inc/ui/class-site-actions-element.php

The request trace attributed at least 240 object-cache reads and six SQL queries to those three page-list loads: 120 uncached-ID checks and 120 WP_Post instance reads. None of the resulting page options were used by the WordPress Dashboard.

The same ordinary Dashboard also enqueued wu-gutenberg-support.js, because Gutenberg_Support::add_scripts() runs on every admin_enqueue_scripts event without checking whether the current screen is a block editor.

Implementation context

Primary files:

• inc/builders/block-editor/class-block-editor-widget-manager.php
• inc/compat/class-gutenberg-support.php
• inc/ui/class-current-site-element.php
• inc/ui/class-my-sites-element.php
• inc/ui/class-site-actions-element.php

Recommended approach:

1. Enqueue Gutenberg support assets only when get_current_screen()->is_block_editor() is true, while preserving any explicitly supported site editor/widget editor contexts.
2. Avoid evaluating expensive field options merely to derive server-side block attribute types.
3. Make the shared page-option list lazy and request-memoized so the three elements do not independently query and hydrate the same pages.
4. Preserve frontend dynamic-block registration and REST block-editor previews.

Tests

• Ordinary Dashboard/Profile screens do not enqueue wu-gutenberg-support.
• Block editor screens still enqueue and localize the script.
• Registering block attributes does not execute page-option providers.
• Consolidating editor settings executes a lazy page provider once per request.
• Dynamic blocks still render on frontend and REST preview requests.

Verification

vendor/bin/phpunit --filter Block_Editor_Widget_Manager_Test
vendor/bin/phpcs inc/builders/block-editor/class-block-editor-widget-manager.php inc/compat/class-gutenberg-support.php inc/ui/class-current-site-element.php inc/ui/class-my-sites-element.php inc/ui/class-site-actions-element.php
vendor/bin/phpstan analyse