diff --git a/packages/ui/jsonrpc/src/server.ts b/packages/ui/jsonrpc/src/server.ts
index 352563f7f2..fe605a8536 100644
--- a/packages/ui/jsonrpc/src/server.ts
+++ b/packages/ui/jsonrpc/src/server.ts
@@ -62,6 +62,7 @@ interface SessionRecord {
 
 /** Recover the delegating parent carried by every service-owned subagent lifecycle event. */
 function subagentParentOf(carrier: Scoped<SubagentService>): Agent {
+  // SubagentService emits this lifecycle pair only through scopeTarget(this, parent).
   return carrierKeyOf(carrier) as Agent
 }