[chubes4]

Related issues

• Fixes Theme pattern files are not registered until the pattern cache is cleared #5158

How AI was used in this PR

Claude (via the Pi coding agent in a Roadie session) found this while comparing Studio Code agent runs, traced it to the code, wrote the change and its test, and ran the verification below. Opened as a draft for human review.

Proposed Changes

• A pattern file added to a theme's patterns/ directory isn't registered on a Studio site until the theme's pattern cache is cleared. That's because WP_Theme::get_block_patterns() only skips its cache in theme development mode, and Studio sites leave WP_DEVELOPMENT_MODE empty. theme.json edits go through a similar cache.
• New and existing sites now get define( 'WP_DEVELOPMENT_MODE', 'theme' ) in wp-config.php when the site doesn't define it already. A site's own value, such as all or '', is never replaced.
• It goes in wp-config.php because WordPress reads the mode in wp_initial_constants(), before mu-plugins load, and caches the result. Defining it from Studio's mu-plugin loader would be too late.
• Trade-off: local sites skip core's theme pattern and theme.json caches. That's what this mode exists for, but it's a default change for every Studio user.

Testing Instructions

1. Create and start a site on Twenty Twenty-Five. wp-config.php contains define( 'WP_DEVELOPMENT_MODE', 'theme' );.
2. Load the front page, then add wp-content/themes/twentytwentyfive/patterns/repro.php with the header Slug: twentytwentyfive/repro.
3. studio wp eval 'var_dump( WP_Block_Patterns_Registry::get_instance()->is_registered( "twentytwentyfive/repro" ) );' prints true. On trunk it prints false until wp_get_theme()->delete_pattern_cache() runs.
4. Change the define to 'all', then restart the site. The value stays 'all'.

Steps 1–4 were run on a throwaway site. npx vitest run apps/cli/lib/native-php/tests/site-setup.test.ts passes.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[chubes4]

Closing in favour of a narrower fix. Measured on a fresh site, WP_DEVELOPMENT_MODE made the front page about twice as slow (median 0.18 s with it off, 0.39 s with theme, 0.47 s with all), because every request rebuilds patterns and global styles. That cost would land on every Studio user just to fix a case that only comes up when a pattern file is added.

The agent now clears that theme's pattern cache (WP_Theme::delete_pattern_cache()) right after it writes a file in patterns/, on the spike in #5146. I checked it end to end: a new pattern that was not registered became registered after the clear. #5158 stays open for people who add pattern files by hand.

AI assistance: Claude (via the Pi coding agent in a Roadie session) took the measurements and wrote this comment, as asked by Chris.