Snap and hover hit-testing scanned the whole model wire set every cursor move; a heavily block-instanced drawing explodes to millions of wires, so this stalled for over a second per move. Add a cached spatial grid (wire_grid) keyed on the geometry epoch and query only the cursor neighbourhood via Scene::hit_test_wires_near. Gate the O(in-range segments squared) intersection passes on the in-range POINT count, not the wire count — a handful of curved wires, each hundreds of tessellated points, blew the quadratic up while the wire count looked modest. Give zero-size entities away from the origin (POINTs) a real cullable AABB, and fall back to a block sub-wire's own world points when its entity bounding box is degenerate.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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