Model shows lanes without a Pool

Reference model C.4.0 shows a lanes but no pool.
Need to be fixed

This seems to be the case when a model contains several  collaboration diagrams - in such case we can open only the first one without additional user UI.

<img width="1447" height="896" alt="Image" src="https://github.com/user-attachments/assets/a72c6d8b-1b97-4d25-ae77-beaddc966361" />