#wrong-collision

A PhysicsHullFile node compiled with import_mode HullPerElement treats a material break as an element boundary. Paint two adjoining primitives with a second material and the compiler folds them into one element and builds one convex hull across both. The convex hull of a wall with a hole in it is a solid wall, so every doorway and window built the same way seals shut at once, with no geometry change in the diff. Every offline check stays green, because none of them compile the model. The defect is only visible in the compiled collision, which the editor or an in-engine walk probe can see. Fix by giving physics its own single-material copy of the source mesh, so the render mesh's material list never reaches the physics node, and pin the physics mesh to the render mesh with a lint.

The render node in a vmdl honours import_rotation. PhysicsHullFile and PhysicsMeshFile ignore it. So correcting an off-axis import with import_rotation fixes the picture and leaves the collision exactly where it was. The model builds clean with no error and no warning, photographs correctly, and a player walks straight through it. Bake a corrected engine-frame copy of the mesh that both the render node and the physics node read, rather than rotating one consumer with a property the other ignores.

A multi-hull vmdl authored with per-shape collision_tags does not get those tags at runtime -- a scene ModelCollider overwrites every shape with the GameObject's own tags, so Scene.Trace.WithoutTags can't filter one hull from another. Split the hulls across separate collider GameObjects instead.