Faithful port of retail UIElement_UIItem::UpdateCapacityDisplay (0x004e16e0):
each container cell (side bags + main pack) shows a vertical UIElement_Meter
(element 0x10000347, back 0x06004D22 / fill 0x06004D23) filled to
GetNumContainedItems / ItemsCapacity, clamped [0,1]; hidden for non-containers
(CapacityFill=-1). Drawn procedurally on UiItemSlot like the triangle/square
overlays (back full + front clipped bottom-up). Right-anchored flush to the cell
edge (visual gate: the dat X=26 sat ~5px off the right edge). Visually confirmed
2026-06-22. Divergence AP-59; polish deferred to ISSUES #146 (exact rect/anchor,
fill direction vs m_eDirection 0x6f, closed-bag lazy-load).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>