Slab is committed by its 3D registry tool, which accumulates the grid:click
vertices the 2D panel emits and commits on close. That path is dead in 2D-only
view — the 3D canvas is display:none, so the tool never commits and the slab is
never created (split/3D work because the 3D side is live). Mirror the zone
pattern: the panel commits the slab itself on both close paths (double-click +
click-first-vertex), gated to viewMode==='2d' so split/3D keep their single-owner
tool commit (no double-create).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
