UOrbdaleTerrainSplineFeatureEditorSubsystem

• Change: a spline's OnSplineChanged and TransformUpdated, and a property change of the component, are hints; the component's key (the sampled points and the parameters) is the truth, so a missed or repeated hint costs a resample.

• Dragging (a hint, then a transaction still open or a mouse button down): the visualizer's preview is evaluated when the key changed, at most once every max(kMinPreviewInterval_s, kPreviewCostFactor x the last evaluation). The ground does not change.

• Release: the edit's transaction finalizing (OnObjectTransacted, Finalized) on the spline, its actor, an attach parent or the component, with no mouse button down; else kQuiet_s with no hint, no button down and no transaction open. The feature is built or replaced in place (same id) through FOrbdaleTerrainFeaturePlacement. When its ground is loaded the commit is stored in the edit's own transaction, so one Ctrl+Z takes back the spline and the ground; over ground still loading it holds (Pending, up to 60 s) and lands later as its own transaction, "Spline feature: <actor>", so that drag takes two undos. A new release replaces a waiting commit with the newest shape.

• Undo and redo never commit; an undo or redo that touches a component cancels its waiting commit.

• Delete: deleting the actor, the component or the spline in the editor removes the feature in the delete's transaction (one Ctrl+Z restores both, same id), or holds and lands later over unloaded ground.

• Copies: a component registered fresh (added, pasted, duplicated or re-keyed, never loaded) builds its own feature at its first release. A construction-script re-run is not a delete.

• Load never commits; components found Missing after a load are listed in one notification with Rebuild all.

• Components inside a Level Instance that is not being edited are left alone.

Experimental: it leans on the experimental USplineComponent::GetOnSplineChanged.