diff --git a/PLAN.md b/PLAN.md
index 4fa5334..7f98a42 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -4,6 +4,8 @@
 
 `Yonexus.Server` is the OpenClaw plugin that acts as the central communication hub in a Yonexus network.
 
+This repository references `Yonexus.Protocol` as a submodule at `protocol/`.
+
 It is responsible for:
 - accepting WebSocket connections from clients
 - maintaining the client registry and trust state