rtx-cfd: the legacy GPU modules back in the cuda build (repair in progress)

crates/specialized/rtx-cfd/src/solvers/lbm/mod.rs

@@ -5,30 +5,27 @@
 //! - D3Q19: 3D model with 19 discrete velocities
 //! - Boundary conditions: bounce-back, Zou-He
 //! - Collision operators: BGK, MRT
-// PERF-2 (2026-09-16): the legacy GPU modules have not compiled since the
-// initial commit (cudarc API drift); kept out of the `cuda` build until
-// someone needs them — the batched V-cycle benchmark uses cudarc directly.
 
 pub mod boundary;
 pub mod d2q9;
 /// GPU-accelerated D2Q9 LBM solver
-// #[cfg(feature = "cuda")]
-// pub mod d2q9_gpu;
+#[cfg(feature = "cuda")]
+pub mod d2q9_gpu;
 pub mod d3q19;
 /// GPU-accelerated D3Q19 LBM solver
-// #[cfg(feature = "cuda")]
-// pub mod d3q19_gpu;
+#[cfg(feature = "cuda")]
+pub mod d3q19_gpu;
 
 pub use boundary::{
     BounceBackBc, BoundaryConditionSet, BoundaryOrientation, LbmBoundaryCondition, ZouHeBc,
     ZouHeBoundaryType,
 };
 pub use d2q9::{D2Q9Parameters, D2Q9Solver};
-// #[cfg(feature = "cuda")]
-// pub use d2q9_gpu::D2Q9GpuSolver;
+#[cfg(feature = "cuda")]
+pub use d2q9_gpu::D2Q9GpuSolver;
 pub use d3q19::{D3Q19Parameters, D3Q19Solver, MacroscopicVariables3D};
-// #[cfg(feature = "cuda")]
-// pub use d3q19_gpu::D3Q19GpuSolver;
+#[cfg(feature = "cuda")]
+pub use d3q19_gpu::D3Q19GpuSolver;
 
 /// Common LBM traits and utilities
 pub mod common {