Queen Imogen's arrival locks the party rooms, forbids entry and exit, and protects the interior from all outside influence or spells.
The crawlers anticipate that the Masquerade acts as a multipart spell and that the queen's presence will complete its isolation. They plan to have Samantha restore inventory and magic access before the seal closes and then break the seal during Donut's performance.
The warning activates while the talent competition is underway and the castle battle rages outside. Once active, no participant can enter or leave before the party concludes, and the external conflict cannot magically affect those inside.
An invisible barrier announced by glowing system text and arcane light across the ballroom exits.
The seal converts the Masquerade into a closed trap and cuts the coalition off from its outside forces.