Optional Readonlymerged1 for an instance that is a merged mesh of static instances
(static-merge.ts). Its transform must stay the identity: a build or
check with anything else throws. That only catches the group's own
record moving: a merged source that moved is only caught when the
scene is assembled again (assembleTraceScene checks the plan).
Optional; omitted means none is merged.
ReadonlymeshThe instance's mesh box in object space, six floats per instance ([min, max]).
ReadonlyobjectObject-to-world, 16 numbers per instance (column-major 4x4).
ReadonlyslotsThe scene's instance slot of each instance.
Readonlyvisible1 when the instance is visible. Hidden instances are in the shape too, with empty boxes while hidden.
What a top-level build needs per instance, as flat arrays that can move to a worker.