fix(renderer): keep draw-order offsets within clipping planes

docs/perspective-depth.md

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+# Perspective draw-order clipping regression
+
+Switching a flat model view from orthographic to perspective could hide otherwise
+visible lines. The camera applied an OpenGL-to-WebGPU depth conversion to a
+projection that already used WebGPU's depth range. The shaders then applied a
+fixed draw-order offset that could push geometry past the far clipping boundary.
+
+The camera now uses the DirectX/WebGPU projection directly. The shared
+`draw_order.wgsl` function keeps the existing offset away from clipping planes
+and reduces it near either plane. Its adjustment is monotonic in draw order,
+leaves neutral geometric depth unchanged, and does not move clipped vertices
+back into range. It is shared by the native and compatibility shader paths.
+
+## GPU reproduction
+
+These are offscreen renders from the application's wire pipelines. All 17 lines
+are on the same plane; only their draw-order values differ. The first two lines
+(red when visible) were clipped in perspective. Both projections now show all
+17 lines. This synthetic drawing contains no user CAD geometry.
+
+| Before | After |
+| --- | --- |
+| ![Two leftmost lines missing](images/perspective-depth-before.png) | ![All 17 lines visible](images/perspective-depth-after.png) |
+
+## Validation
+
+```sh
+cargo test --locked --lib
+cargo test --locked --lib scene::pipeline::depth_tests -- --ignored --nocapture
+```
+
+The GPU tests exercise storage and packed wire pipelines, near/far clipping,
+coplanar draw order in both submission orders, and wire occlusion by a triangle
+mesh. Normal tests check camera depth endpoints, picking, and validation of all
+14 composed draw-order shaders.
+
+Set `OCS_DEPTH_TEST_IMAGES` to an output directory to save the orthographic and
+perspective reproduction images while running the GPU tests.