fix(api): consumer rejects malformed heartbeats with no host block (no phantom hosts)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend-nest/src/services/host-agent-consumer.service.ts

@@ -88,6 +88,12 @@ export class HostAgentConsumerService implements OnApplicationBootstrap {
 
   private async onHeartbeat(licenseId: string, payload: HeartbeatPayload): Promise<void> {
     if (!(await this.isValidTenant(licenseId))) return;
+    // A well-formed v2 heartbeat always carries a host block. Reject malformed
+    // payloads so a stray/empty publish can't create a phantom host row.
+    if (!payload || typeof payload.host !== 'object' || payload.host === null) {
+      this.logger.warn(`ignoring malformed heartbeat for license ${licenseId} (no host block)`);
+      return;
+    }
     const now = new Date();
 
     await this.updateLegacyConnection(licenseId, now);