fix(hatch): finite GPU sentinel for boundary loop separators (#386, #416)

Hatch/wipeout boundary sub-loops were separated by NaN vertices that the
fill shaders detected with `p.x == p.x`. Intel Mesa folds that NaN
self-compare to `true` under fast math, so separators read as real
vertices, the ray-cast crossing count broke, and fills bled outside
their boundary — only on Intel iGPUs. GPU uploads now rewrite the
separators to a finite 1e30 sentinel (GPU_BOUNDARY_SEP) and the shaders
test `abs(x) < 1e29`, which every driver evaluates identically. The
CPU-side NaN representation is unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scene/pipeline/wipeout_gpu.rs

@@ -310,12 +310,14 @@ impl WipeoutGpu {
             .take(MAX_HATCH_BOUNDARY_VERTS)
             .enumerate()
         {
-            // Preserve NaN separators — they signal path breaks to the
-            // in_polygon ray-cast, must not be shifted into finite numbers.
+            // Path-break separators go up as the finite GPU sentinel, not
+            // NaN — the shader NaN self-compare is folded to `true` on some
+            // drivers (#386, #416) — and must not be shifted by `drift`.
             if x.is_finite() && y.is_finite() {
                 boundary_data.verts[i] = [x + drift[0], y + drift[1], 0.0, 0.0];
             } else {
-                boundary_data.verts[i] = [f32::NAN, f32::NAN, 0.0, 0.0];
+                let s = crate::scene::model::hatch_model::GPU_BOUNDARY_SEP;
+                boundary_data.verts[i] = [s, s, 0.0, 0.0];
             }
         }