diff --git a/node/src/db.ts b/node/src/db.ts
index b51cbab..0dbe158 100644
--- a/node/src/db.ts
+++ b/node/src/db.ts
@@ -294,6 +294,7 @@ export class MailboxStore {
     this.waiters.delete(oldName);
   }
 
+  /** @internal Test helper to wait for a long-poll waiter to register. Not part of the public contract. */
   waiterCount(name: string): number {
     return this.waiters.get(name)?.size ?? 0;
   }