[benchan0527]

Summary

• Vertex-to-vertex snapping (Key V): Allows snapping a scenery object to another object by matching a selected vertex from the source object to a target vertex on another object, translating the whole source object accurately.
• Edge-to-edge snapping (Key L): Allows aligning and snapping a scenery object along an edge of another object or along a road/spline:
  • Supports full 3D rotation alignment or horizontal-only yaw alignment (Shift key).
  • Works with mesh edges (including complex models up to 200,000 edges) and object bounding box edges.
  • Supports snapping to road splines as target edges.
• UI & Controls:
  • Added dedicated snap buttons in the top toolbar and in the right-side Scenery Object properties panel.
  • Interactive visual overlay: shows highlighted glowing vertices and edge lines, depth-culled nearest raycast picking, and a connecting guide line while picking.
  • Registered in Command Palette (Ctrl+P -> "Snap Vertex to Vertex", "Snap Edge to Edge").
  • Mutually exclusive activation between vertex snap and edge snap modes.
• Asset path normalization: Normalized backslashes and slashes in asset lookup keys so models located in subfolders load reliably on all platforms.

Test plan

• Select a scenery object, press V (or click the vertex snap button in toolbar/properties panel): glowing red vertices appear. Click a vertex on the source object, then click a target vertex on another object; confirm the source object snaps cleanly to align the two vertices.
• Select a scenery object, press L (or click the edge snap button): orange wireframe edges appear. Click a source edge, then click a target edge on another object or road spline; confirm the source object rotates and translates to align along the target edge.
• Hold Shift while clicking a target edge in edge snap mode; confirm rotation is constrained to horizontal yaw only.
• Test on a large complex scenery object (e.g. northkcnewnew2.sco with >30k edges); confirm all edges render and are selectable without crashing or freezing.
• Press Esc at any time during snapping to cancel cleanly without altering the scene.
• Run cargo test --bin openmapper snap; confirm all unit tests pass.