Result of initPicking. All four fields are undefined when
the scene has no picking consumers / no scene loader / no LuxarScene root, in which
case picking is intentionally inactive for this session.
Reads the per-element keys CSR (issue #1917). A LabelLoader on the
'keys' channel — same class, different array names — so it caches,
coalesces and disposes exactly like the label one.
Result of initPicking. All four fields are
undefinedwhen the scene has no picking consumers / no scene loader / no LuxarScene root, in which case picking is intentionally inactive for this session.