Move wp_load_classic_theme_block_styles_on_demand() from the init action to wp_default_styles

Author: westonruter

src/wp-includes/default-filters.php

@@ -607,7 +607,7 @@
 add_action( 'enqueue_block_assets', 'wp_enqueue_classic_theme_styles' );
 add_action( 'enqueue_block_assets', 'wp_enqueue_registered_block_scripts_and_styles' );
 add_action( 'enqueue_block_assets', 'enqueue_block_styles_assets', 30 );
-add_action( 'init', 'wp_load_classic_theme_block_styles_on_demand', 8 ); // Must happen before register_core_block_style_handles() at priority 9.
+add_action( 'wp_default_styles', 'wp_load_classic_theme_block_styles_on_demand', 0 ); // Must happen before wp_default_styles() and register_core_block_style_handles().
 /*
  * `wp_enqueue_registered_block_scripts_and_styles` is bound to both
  * `enqueue_block_editor_assets` and `enqueue_block_assets` hooks

src/wp-includes/script-loader.php

@@ -3674,6 +3674,9 @@ function wp_remove_surrounding_empty_script_tags( $contents ) {
 /**
  * Adds hooks to load block styles on demand in classic themes.
  *
+ * This function must be called before {@see wp_default_styles()} and {@see register_core_block_style_handles()} so that
+ * the filters are added to cause {@see wp_should_load_separate_core_block_assets()} to return true.
+ *
  * @since 6.9.0
  *
  * @see _add_default_theme_supports()