Harden pattern for room name.

Author: peterwilsoncc

src/wp-includes/collaboration/class-wp-http-polling-collaboration-server.php

@@ -159,7 +159,13 @@ public function register_routes(): void {
 			'room'      => array(
 				'required'  => true,
 				'type'      => 'string',
-				'pattern'   => '^[^/]+/[^/:]+(?::\\S+)?$',
+				/*
+				 * Room names follow the pattern EntityKind/EntityName:ObjectID, where:
+				 * - EntityKind is a broad category of the entity, e.g. 'postType'.
+				 * - EntityName is the specific entity, e.g. 'post', 'page'.
+				 * - ObjectID is an optional identifier for single entities, e.g. a specific post ID. It must be a positive integer.
+				 */
+				'pattern'   => '^[^/]+/[^/:]+(?::[1-9][0-9]*)?$',
 				'maxLength' => 191, // Matches $max_index_length in wp-admin/includes/schema.php.
 			),
 			'updates'   => array(