Smallest camera-to-pivot distance the orbit system allows
(ControlsManager.minPivotDepth()): auto-frame's min distance limit when
set, capped at sceneScale·1e-3. The fly-target derivation floors the
reused pivot depth here, so any depth reachable through orbit interaction
round-trips exactly while flying inside the floor can't collapse the
pivot onto the camera.
State saveCameraState / restoreCameraState share with the
ControlsManager: the camera, the active control instance, scene scale and the minimum pivot depth, plus the manager-owned snapshot vectors (position, rotation, up, target) they read from and write into in place.