diff --git a/capiscio_mcp/events.py b/capiscio_mcp/events.py
index 4bb32c7..197a834 100644
--- a/capiscio_mcp/events.py
+++ b/capiscio_mcp/events.py
@@ -151,7 +151,7 @@ def emit_policy_enforced(
         # See capiscio-server internal/db/models.go for JSON field tags.
         event: Dict[str, Any] = {
             "id": str(uuid.uuid4()),
-            "agentId": effective_agent_id or str(uuid.UUID(int=0)),
+            "agentId": effective_agent_id or "",  # empty string: server will return clear validation error instead of silently dropping the event
             "traceId": str(uuid.uuid4()),
             "eventType": self.EVENT_POLICY_ENFORCED,
             "severity": severity or ("HIGH" if decision == "DENY" else "INFO"),