The shared polygon-vertex affordance snapped via snapPointToGrid(rawPoint), whose
default step is the hardcoded WALL_GRID_STEP (0.5m) — so slab/zone/ceiling vertex,
edge, and add-vertex edits always quantized to half-meters regardless of the
active mode OR the user's grid-step setting (plan open bugs #1-2). Use the
mode-aware getSegmentGridStep() (0 in non-grid modes) so grid quantizes to the
live step, lines/off pass through to the wall-snap/alignment resolver. Drop the
legacy shiftKey bypass from the slab/ceiling magnetic resolvers (they already
gate on isMagneticSnapActive).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
