Column exposes shaft / base / capital / frame slots on node.slots (base when
baseStyle!=none, capital when capitalStyle!=none, frame only for non-vertical
support styles). The single material context is widened to a per-slot map plus
a ColumnSlotContext; each part subtree is wrapped in <ColumnSlot> so every
mesh primitive resolves its material AND stamps userData.slotId from the same
context. Decorative shaft parts inherit shaft, base/capital carvings inherit
their parent slot. Resolution: textures-off wall role -> node.slots ref ->
legacy material/preset -> declared default (shaft/base/capital concrete-plaster,
frame metal-steel). Monochrome unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
