aurora: add asynchronous OpenXR stereo replay bridge

aurora-main/lib/gfx/stereo_replay.hpp

@@ -4,6 +4,22 @@
 
 namespace aurora::gfx::stereo_replay {
 
+// An OpenXR eye supplies the shape of its asymmetric frustum, but the sealed
+// GX draw already contains the depth mapping adjusted for that draw's GX
+// viewport and Aurora's reversed-Z convention. Replacing the complete matrix
+// would pair an unrelated depth range with the original pipeline compare and
+// clear state, which can reject the entire eye. Replace only the four
+// perspective-frustum coefficients and preserve every depth-related element.
+inline Mat4x4<float> compose_projection(const Mat4x4<float>& eyeFrustum,
+                                        const Mat4x4<float>& gameProjection) noexcept {
+  Mat4x4<float> out = gameProjection;
+  out.m0[0] = eyeFrustum.m0[0];
+  out.m0[2] = eyeFrustum.m0[2];
+  out.m1[1] = eyeFrustum.m1[1];
+  out.m1[2] = eyeFrustum.m1[2];
+  return out;
+}
+
 // Aurora stores the GX 3x4 matrices row-major. The vertex shader consumes
 // them as vec4 * mat3x4, which is equivalent to the original column-vector
 // affine transform. Applying an eye-space delta therefore composes delta *