Beacons — a collision cube for anything abstract that has a position

A lamp is a LIGHT. It has a position, it can be moved, it appears in the piece list — and there is nothing in the scene to click, because a Babylon light has no geometry. Selecting the lantern meant finding it in the list every time, and the report was blunt: "I can't move the lantern (or select it by clicking on it)."

Two different faults produced that one sentence, and only one of them is here. The other was that lamp never claimed its light as the piece's BODY, so the editor wrote a new position into the file with nothing in the scene to write it to — see body in features-scene.ts.

Only where a feature says so

A beacon is not given to every bodiless piece. Most environment primitives have no location for one to mark: a skybox is everywhere, fog and ambient are settings, and sun's at is a DIRECTION — a dot floating at [-0.5, 1, 0.4] would be a confident lie about where the sun is. Three junk dots near the origin is what the blanket rule produces.

So the feature declares it, next to its icon and its schema: marker: true means "this puts a real thing at at, and it cannot be seen". A consumer's feature gets a beacon the same way it gets an icon, which is the property that makes the registry worth having.

A CUBE, not a sphere: it is a stand-in for a thing rather than a thing. Owner: "really we should provide a simple collision cube for any abstract thing that has a position that we might need to select" — and the generality is the point. Lamps are the case that surfaced it; positional sound, a placed camera, and later reference points and zones are the same shape of problem.

Invisible, and that is not a contradiction

The first version drew an amber cube. It works, and it is clutter: a solid the author cannot move, delete or edit, sitting in a view whose whole purpose is judging an arrangement. A COLLISION cube is what was asked for, and collision geometry is not seen.

⚠️ This is only pickable because we pass our own predicate. Babylon's default picking test is isEnabled() && isVisible && isPickable, so an invisible mesh is normally unpickable — but pickPiece supplies a predicate, and Babylon consults the predicate INSTEAD of that test rather than as well as it. An invisible collision proxy therefore works here and would silently stop working for any caller that picks without a predicate. Verified by ray rather than reasoned about, because "it should still be pickable" is exactly the kind of claim this project has been wrong about before.

Finding it without seeing it is not the problem it sounds like: a lamp is already visible as the light it casts, and it is a row in the piece list. What it needed was somewhere for a ray to land.