fix(render): don't apply the draw-order z-bias to 3D mesh outline edges

Mesh (PolyfaceMesh / PolygonMesh) outline edges are drawn through the wire
pipeline, whose shader pulls each wire toward the camera by
draw_depth * DRAW_ORDER_BIAS (0.001) for 2-D draw-order layering. Every
entity gets a draw_depth in [-1, 1], so a mesh's edges were pulled forward
too — and when the mesh's depth extent projects to less than the bias (a
small or distant mesh), its hidden back-face edges peeked through its own
shaded fill. Solid feature edges use the mesh shader, which has no such
bias, which is why only meshes showed it and why adjusting the fill's depth
bias had no effect.

3-D mesh outline edges are real geometry occluded by true depth, so force
their draw_depth to 0 (they are already grouped as `mesh_edge` in
upload_wires). They now occlude exactly like solid edges.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/scene/pipeline/wire_gpu.rs

@@ -441,7 +441,12 @@ impl WireGpu {
                 .par_iter()
                 .enumerate()
                 .map(|(idx, w)| {
-                    emit_wire_native(w, idx as u32, w.color, wire_draw_depth(w, depth_map))
+                    // 3D mesh outline edges are real geometry occluded by true
+                    // depth — they must NOT take the draw-order z-bias (which
+                    // pulls 2D wires toward the camera), or the hidden edges of a
+                    // small / distant mesh peek through its own shaded fill.
+                    let dd = if mesh_edge { 0.0 } else { wire_draw_depth(w, depth_map) };
+                    emit_wire_native(w, idx as u32, w.color, dd)
                 })
                 .collect();
             let mut instances: Vec<WireInstance> =
@@ -474,7 +479,10 @@ impl WireGpu {
             let _ = const_bgl;
             let per: Vec<Vec<WireInstance>> = wires
                 .iter()
-                .map(|w| emit_wire_instances(w, w.color, wire_draw_depth(w, depth_map)))
+                .map(|w| {
+                    let dd = if mesh_edge { 0.0 } else { wire_draw_depth(w, depth_map) };
+                    emit_wire_instances(w, w.color, dd)
+                })
                 .collect();
             let mut instances: Vec<WireInstance> =
                 Vec::with_capacity(per.iter().map(Vec::len).sum());