diff --git a/packages/core/src/session.ts b/packages/core/src/session.ts
index 4483c67f..e1e1f5b7 100644
--- a/packages/core/src/session.ts
+++ b/packages/core/src/session.ts
@@ -1661,7 +1661,7 @@ ${agentInstructions}
       contentParts.push(`Failed to kill processes: ${failedPids.join(", ")}.`);
     }
 
-    this.onAssistantMessage(this.buildUserMessage(sessionId, { text: contentParts.join(" ") }), false);
+    this.onAssistantMessage(this.buildSystemMessage(sessionId, contentParts.join(" ")), false);
   }
 
   private isInterrupted(sessionId: string): boolean {