diff --git a/sim/cluster0/cluster.env b/sim/cluster0/cluster.env
index 4a17875..1bba49f 100644
--- a/sim/cluster0/cluster.env
+++ b/sim/cluster0/cluster.env
@@ -19,6 +19,7 @@ PRIMARY_DB_PORT=3306
 
 ARTC0_HOST=artc0
 ARTC0_IP=10.7.16.128
+# DEPRECATED: legacy dev VM — FE/compose no longer target artc0; kept for DNS cleanup only.
 
 SSH_USER=ai
 
@@ -58,8 +59,8 @@ GITEA_ORG=ac
 LAB_PUBLIC_ORIGIN=https://acl0.f0xx.org
 PUBLIC_ORIGIN=https://apps.f0xx.org
 SHORT_LINKS_PUBLIC_BASE=https://s.f0xx.org
-# Lab cluster → prod url-shortener (cast01 has no outbound :443 to s.f0xx.org; use BE vhost + Host)
-URL_SHORTENER_API_BASE=http://artc0.intra.raptor.org
+# Staging cluster url-shortener API (internal HTTP + Host header)
+URL_SHORTENER_API_BASE=http://cast01.intra.raptor.org
 URL_SHORTENER_API_HOST=s.f0xx.org
 FE_PROXY_TARGET=cast01.intra.raptor.org:80