Comment: Send announce for all new comments

.github/changelog/1562-from-description

@@ -0,0 +1,4 @@
+Significance: minor
+Type: added
+
+Incoming interactions create an Announce activity so other instances get notified about it.

includes/collection/class-interactions.php

@@ -330,8 +330,9 @@ public static function activity_to_comment( $activity ) {
 			'comment_date'         => \get_date_from_gmt( \gmdate( 'Y-m-d H:i:s', \strtotime( $date ) ) ),
 			'comment_date_gmt'     => \gmdate( 'Y-m-d H:i:s', \strtotime( $date ) ),
 			'comment_meta'         => array(
-				'source_id' => \esc_url_raw( object_to_uri( $activity['object'] ) ),
-				'protocol'  => 'activitypub',
+				'source_id'             => \esc_url_raw( object_to_uri( $activity['object'] ) ),
+				'protocol'              => 'activitypub',
+				'_activitypub_activity' => $activity,
 			),
 		);
 

includes/scheduler/class-comment.php

@@ -7,6 +7,8 @@
 
 namespace Activitypub\Scheduler;
 
+use Activitypub\Activity\Activity;
+use Activitypub\Collection\Actors;
 use Activitypub\Comment as Comment_Utils;
 
 use function Activitypub\add_to_outbox;
@@ -45,9 +47,12 @@ public static function schedule_comment_activity( $new_status, $old_status, $com
 		}
 
 		$comment = get_comment( $comment );
+		if ( ! $comment ) {
+			return;
+		}
 
-		// Federate only comments that are written by a registered user.
-		if ( ! $comment || ! $comment->user_id ) {
+		if ( ! $comment->user_id ) {
+			self::maybe_announce_interaction( $new_status, $old_status, $comment );
 			return;
 		}
 
@@ -81,6 +86,54 @@ public static function schedule_comment_activity( $new_status, $old_status, $com
 		add_to_outbox( $comment, $type, $comment->user_id );
 	}
 
+	/**
+	 * Announce an interaction.
+	 *
+	 * When a comment is received from another ActivityPub instance and approved,
+	 * this method creates an Announce activity so the blog's followers are notified
+	 * about the interaction.
+	 *
+	 * @param string      $new_status The new comment status.
+	 * @param string      $old_status The old comment status.
+	 * @param \WP_Comment $comment    The comment object.
+	 */
+	public static function maybe_announce_interaction( $new_status, $old_status, $comment ) {
+		// Only if we're in both Blog and User modes.
+		if ( ACTIVITYPUB_ACTOR_AND_BLOG_MODE !== \get_option( 'activitypub_actor_mode', ACTIVITYPUB_ACTOR_MODE ) ) {
+			return;
+		}
+
+		if ( 'approved' !== $new_status || 'approved' === $old_status ) {
+			return;
+		}
+
+		if ( ! Comment_Utils::was_received( $comment ) ) {
+			return;
+		}
+
+		// Get activity from comment meta.
+		$activity = \get_comment_meta( $comment->comment_ID, '_activitypub_activity', true );
+
+		// Validate activity structure.
+		if ( ! $activity || ! \is_array( $activity ) ) {
+			return;
+		}
+
+		// Ensure object exists in the activity.
+		if ( empty( $activity['object'] ) || ! \is_array( $activity['object'] ) ) {
+			return;
+		}
+
+		// Create the Announce activity.
+		$announce = new Activity();
+		$announce->set_type( 'Announce' );
+		$announce->set_actor( Actors::BLOG_USER_ID );
+		$announce->set_object( $activity );
+
+		// Add to outbox with error handling.
+		add_to_outbox( $announce, null, Actors::BLOG_USER_ID, ACTIVITYPUB_CONTENT_VISIBILITY_PUBLIC );
+	}
+
 	/**
 	 * Schedule Comment Activities on insert.
 	 *