Entity identity

An entity has two ids. They are not interchangeable.

EntityUuid          128-bit persistent id
                    survives save, load, and an editor restart
                    references and serialization use this

EntityHandle        slot index + generation
                    process-local
                    stale after the slot is reused
                    not serialized

EntityRegistry
    EntityUuid  ↔  EntityHandle

EntityUuid is the same text form as the TypeScript entity id (8-4-4-4-12). ObjectId is still the bootstrap drawable slot. It is not either of these.

The component stack is membership over those records, not a new id. ADR-0048. A mesh actor's stack names Transform and Mesh Renderer and still carries that object's ObjectId and MeshId. The Perspective camera is not on any stack.

The other ids are not authoring identity either. ADR-0040:

EntityUuid                         persistent authoring identity
EntityHandle                       slot + generation, not serialized
LightId, ProbeId, MeshId,
MaterialInstanceId, FrameId,
ObjectId                           subsystem implementation identity
RenderInstanceId                   extracted rendering identity

Hot lookups use the handle. Resolving a handle is one slot read. A wrong generation returns stale. It does not scan UUIDs. The UUID is how the editor, a save file, and a reference name the same entity.

The registry record has a name and a parent handle. It still does not store component payloads. Membership is SceneWorld's classification of the handle: which mesh, light, probe, or world-settings record owns it. frame_of(handle) reaches a mesh, a light, a probe, or a frame anchor. World Settings has no frame. A future component store would hang off this id. It is not a second registry, and it is not a second outliner.

A duplicate mints a new UUID and a new handle. It copies the parent, the name, and the subsystem record that owns the source: a new object that shares the mesh, a new LightId, or a new ProbeId. Retiring an authorable entity removes that record too. The old handle does not resolve, even if a new entity reuses the slot. ADR-0041.

The render snapshot copies the UUID so a frame can name its source. It does not copy the handle into a file format. The id is not in the C header.

Parse accepts the canonical text, versions 1 through 8, variant 8, 9, a, or b. The nil id is version 0 and is rejected. A second insert of the same uuid is rejected. New ids are version 4. The outliner did not change that.

A .jarviglevel file stores EntityUuid, name, parent uuid, and components. It does not store EntityHandle or ObjectId. ADR-0045.

Deleting a parent reparents each child to no parent before the slot is retired. entity_parent then returns Ok(None), not a stale handle. A scene file can store that. World Settings cannot be duplicated, deleted, or reparented.

The outliner is a view of this registry. World is not an entity. Row identity is the uuid. The label is the name, with a class suffix (Mesh, Light, Probe, World) that is not a second id. Components are inspector sections, not outliner rows. Selection is JRV-0062. The inspector is JRV-0063 and reads the same uuid. The Perspective camera is still not an entity. ADR-0033.

Later viewport picking should follow the snapshot uuid, not the bootstrap slot:

pixel or primitive hit
    -> RenderInstance
    -> EntityUuid
    -> SelectionService
    -> outliner and inspector

The reverse uuid-to-handle lookup still scans. Hot runtime code does not use it. An index can replace that scan later without changing either id.