the candidate document (typically JSON.parse output)
the registered upgrade steps
Optionaloptions: Omit<MigrateSceneDocumentOptions, "targetVersion">
lossy-change reporting (targetVersion is ignored: the result
has to be a document this build can validate)
the canonical, frozen document at SCENE_FORMAT_VERSION
FourError / TypeError exactly as runSceneMigrations, then as
validateSceneDocument
Upgrades
valueto the current scene format and validates it (§79, §80).The one call a loader needs: it accepts a document of any version the registered chain can reach SCENE_FORMAT_VERSION from — including the current version, which passes straight through to validation — and returns a canonical SceneDocument ready for
instantiateScene.