Comments: Load on public-api after switching to the target blog (#53958)

Author: arcangelini

projects/packages/jetpack-mu-wpcom/changelog/fix-comments-public-api-blog

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Comments: Keep headings in P2 comments edited through the REST API.

projects/packages/jetpack-mu-wpcom/src/class-jetpack-mu-wpcom.php

@@ -839,6 +839,14 @@ private static function should_disable_comment_experience( $blog_id ) {
 	 * Load Verbum Comments.
 	 */
 	public static function load_verbum_comments() {
+		// public-api boots on its own blog, so decide once the request has switched to its target.
+		if ( 'public-api.wordpress.com' === wp_parse_url( home_url(), PHP_URL_HOST ) ) {
+			// Now, for reads across sites that never switch: avatars only touch comments with our stored photo.
+			\Automattic\Jetpack\Comments\Avatars::init();
+			add_action( 'rest_api_switched_to_blog', array( __CLASS__, 'load_verbum_comments' ) );
+			return;
+		}
+
 		if ( class_exists( 'Verbum_Comments' ) ) {
 			return;
 		} else {
@@ -865,8 +873,8 @@ public static function load_verbum_comments() {
 
 	/**
 	 * Register Jetpack Comments' browser-facing routes ahead of the comment
-	 * experience gates. admin-ajax is is_admin(), and a public-api request runs
-	 * plugins_loaded on the wrong blog, so load_verbum_comments() skips both.
+	 * experience gates. admin-ajax is is_admin(), so load_verbum_comments() skips it,
+	 * and on public-api it waits for the blog switch, which comes after rest_api_init.
 	 * Runs on every request, blog 1 and P2s included, on purpose: the routes
 	 * gate themselves on Comments::is_enabled(), as Posts_To_Podcast_Endpoint does.
 	 */