NotConstructible

The event cannot be constructed under this harness's topology at all.

The in-tree instances are the shared in-process meshes and the room hub: both ends come off one loom (or off looms sharing one registry), so there is no 2-peer transport under the pair to drop, and a peer going away is the distinct membership-drain event — which several of them prove instead.

The suite requires the injection hook to return false (a harness that can inject the event has just demonstrated it is constructible) and then refutes the stated reason the one way it is cheaply refutable — see this file's KDoc for what that leaves undetected. This is the weaker arm, and the difference between it and Gap is prose, so prefer Gap whenever the honest answer is "nobody has wired this up yet".