The backing GPU context or device was lost (§61).
Emitted after the renderer has marked itself lost, so a listener observing the renderer sees the lost state. Not an error: nothing is thrown, no FourError is raised, and the application keeps running.
The context or device was restored and engine-owned GPU resources have been re-created (§61).
Emitted after re-creation, so the first render a listener triggers in
response already draws normally.
Events a renderer emits (§61, §6b).
Both payloads carry the renderer itself, because one application may run several (a main view plus an off-screen pass) and a shared listener has to be able to tell which one lost its context.